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Comparison of soil microorganism abundance and diversity in stands of European aspen (Populus tremula L.) and hybrid aspen (Populus tremuloides Michx. x P. tremula L.)/Mulla mikroorganismide arvukuse ja mitmekesisuse vordlus hariliku haava (Populus tremula L.) ning hubriidhaava (Populus tremuloides Michx. x P. tremula L.) puistutes.

INTRODUCTION @@ The use of short rotation forest tree species has been increasing worldwide since the 1970s (Stanton et al., 2002). One of the suitable tree species for the climatic conditions of the Baltic region is hybrid aspen (Populus tremuloides Michx. x P. tremula L.).

Hybrid aspen has been traditionally cultivated on former agricultural lands (since 1999 in Estonia) (Tullus et al., 2007) or on contaminated soils, and since 2000 in oil shale opencasts in Estonia (Tullus et al., 2008). Nevertheless, taking into account the possible environmental impacts of monospecific plantations with one tree species, cultivation of hybrid aspen is not recommended on traditional forest lands in Estonia (Tullus, 2010). In Latvia the genetic selection of hybrid aspen began in the 1960s and new scientific plantations have been established in recent decades (Zeps et al., 2008). At present there are over 4500 ha of hybrid aspen plantations in Northern Europe (Tullus et al., 2012).

Fast growing tree species can be favourable for the environment by decreasing soil erosion and surface runoff due to their root system and vegetation in comparison to conventional agriculture. This positive effect is detectable already in three to five years even in eroded soils (Mann & Tolbert, 2000). The possible adverse effects to the environment in the context of soil are connected with increased demand of nutrients. It is estimated that in poplar plantations the maximum uptake of nutrients occurs at the age of 5-6 years (Nelson et al., 1987), but for aspen stands in boreal climate it is observed that at the age of 9 years a rapid increase in annual biomass production occurs. Because of high establishment costs, hybrid aspen plantations are usually established with low planting densities. Thus the initial productivity per hectare is rather low and maximum nutrient uptake occurs at an older age compared to poplars and natural aspen stands; for example, the nutrient content in the above-ground biomass of 7-year-old hybrid aspen plantations could be only 0.5-3.5% of the total soil nutrient pool (Tullus et al., 2009). In addition, the growth of fast growing tree clones (Salix and Populus spp.) is characterized by increased litter amounts and an elevated C/N ratio and lignin content in the litter (Baum et al., 2009).

Cultivation of short rotation energy crops on former agricultural soils differs from agricultural practices with reduced soil tillage, which in long term can cause changes in the vertical distribution of soil microorganisms: an increased microbial biomass in the upper 5 cm of soil and a decreased biomass in subsoil (Makeschin, 1991). Cultivation of poplars and willows introduces ectomycorrhizal fungi in the former agricultural soils that normally contain saprophytic fungi and increases the diversity of basidiomycetes in general (Lynch & Thorn, 2006). In Germany Baum & Hrynkiewicz (2006) in their investigation of the rhizosphere and bulk soil of two willow clones (Salix viminalis and S. x dasyclados) differing in their mycorrhizal colonization and the decomposition rates of their litter found the species composition of saprophytic fungi to be tree clone specific. The lower mycorrhizal colonization and higher litter decomposition rate of S. viminalis brought about a higher number of saprophytic fungal species. The authors found that colonization densities of seven saprophytic species (Acremonium butyri, Cladosporium herbarum, Cylindrocarpon destructans, Penicillium janthinellum, Penicillium spinulosum, Plectosphaerella cucumerina, and Trichoderma polysporum) significantly correlated with the acid-phosphatase and arylsulphatase activity in the rhizosphere. It is known that also Populus species and clones can differ in their mycorrhizal colonization rate and species composition as it was detected in the investigation of Populus trichocarpa and P. tremula L. x P. tremuloides Michx. (Baum & Makeschin, 2000) and that hybrid aspen (P. tremuloides Michx. x P. tremula L.) has an increased root biomass in comparison to European aspen (Nikula et al., 2009). Other investigations exist about the mycorrhizal colonization of Populus spp. (Cripps & Miller, 1995; Kaldorf et al., 2004) but there is a lack of information regarding the species composition of saprophytic fungi and bacteria in the soil of these trees. In the review article of Tullus et al. (2012) the authors conclude that there is a need for deeper investigations considering the environmental and biodiversity impact of hybrid aspen plantations.

The aim of our investigation was to compare soil microbial populations, mainly saprophytic fungi and bacteria, in hybrid aspen (P. tremuloides Michx. x P. tremula L.) and European aspen (P. tremula L.) plantations on former agricultural lands. The hypothesis was that hybrid aspen plantations would cause changes in soil microbial composition especially in prolonged cultivation periods in comparison to European aspen plantations.

MATERIALS AND METHODS

Description of aspen and hybrid aspen stands and soil sampling

Soil in four hybrid aspen and four European aspen stands growing on former agricultural soils was analysed (Fig. 1). Information about the stands, tree age, and sampling time is given in Table 1. In each stand 10 soil samples (500 g) were taken in the upper soil layer (0-15 cm) and 10 in the deeper soil layer (16-30 cm). In Kalsnava soil samples were taken diagonally through both stands. In other stands samples were taken randomly from various aspen clones planted in parcels in the middle of every parcel. All together 160 soil samples were analysed. Samples were placed in sterile plastic bags (Nasco WHIRL-PAK) and stored at +4 [degrees]C for a few days until the plate count of culturable microorganisms was made. After that the samples were stored at -20 [degrees]C.

[FIGURE 1 OMITTED]

Physical and chemical analyses of soil

Soil moisture content was determined according to the ISO 11465 standard method for every soil sample. The pH of the soil samples was measured in distilled water according to the method ISO 10390. Soil physical and chemical analyses of four soil samples from every aspen stand in three replicates were made in the laboratory of Forest Regeneration and Establishment Group of the Latvian State Forest Research Institute 'Silava'. The following methods were used: LVS ISO 11464 (2006) Soil quality--Pretreatment of samples for physico-chemical analysis, LVS ISO 11465 (2006) Soil quality--Determination of dry matter and water content on a mass basis--Gravimetric method, LVS ISO 11277 (2010) Soil quality--Determination of particle size distribution in mineral soil material Method by sieving and sedimentation, LVS ISO 11261 (2002) Soil quality Determination of total nitrogen--Modified Kjeldahl method, LVS ISO 10694 (2006) Soil quality--Determination of organic and total carbon after dry combustion (elementary analysis), LVS ISO 10693:1995 Soil quality--Determination of carbonate content--Volumetric method, LVS ISO 11466:1995 Soil quality Extraction of trace elements soluble in aqua regia, LVS 398 (2002) Soil quality Determination of total phosphorus. The content of humic acids was determined according to the method of Zaccone et al. (2009).

Analysis of culturable soil microorganisms

In order to estimate the number of colony forming units (CFU) of culturable filamentous fungi (CFF), yeasts, and bacteria by the plate count method, soil sample dilutions were prepared by adding 10 g of soil to 90 mL of sterile distilled water. Suspensions were homogenized on a horizontal shaker for 1 h. After that serial dilutions were prepared, and 0.1 mL of dilutions [10.sup.-2], [10.sup.-3], [10.sup.-4], and [10.sup.-5] were analysed. Agarised tryptic soy (Biolife, Italy) medium (TSA) was used for the enumeration of saprophytic bacterial CFU. The incubation time was 3 days, temperature 20 [+ or -] 2 [degrees]C. Agarised malt extract (MEA), 30 g/L, pH 5.5 (Biolife, Italy), was used as a growing medium that is favourable for fungi, yeasts, and maltose using bacteria. Rose Bengal agar (RBA) with chloramphenicol (Biolife, Italy) was used for the enumeration of fungi and yeasts. The incubation time for fungi was 5 days, temperature 20 [+ or -] 2 [degrees]C. The number of CFU was expressed per gram of dry soil.

Genera of CFF were determined after 10 days of incubation according to morphological characteristi[C.sub.s] and light microscopy results.

Extraction of total soil DNA and quality control

Total soil DNA was extracted using the PowerSoilo DNA Isolation Kit (MO BIO Laboratories, Inc., USA), which uses harsh lysis for the DNA extraction. Samples (250 mg) were homogenized using a horizontal Mixer Mill Type MM 301 (Retsch, Germany) at a maximal speed of 30 Hz (1800 oscillations/min) for 10 min. The amount and purity of the DNA were determined spectrophotometrically using Ultrospec 3100 Pro (Amersham Biosciences, UK) at wavelengths of 230, 260, and 280 nm in order to assess the contamination with proteins and humic compounds (Y eates et al., 1998).

ARDRA of soil DNA

For the amplified ribosomal DNA gene analysis (ARDRA) the fungal rRNA gene region that contains two internal transcribed spacers (ITS) and the 5.8S rRNA gene (ITS1-5.8S-ITS2) was amplified with the primers ITS1F (Gardes & Bruns, 1993) and ITS4 (White et al., 1990). In order to obtain the fingerprints of bacterial populations, the 16S region of bacterial ribosomal RNA was amplified with primers FORB and REVB (Edwards et al., 1989; Yeates et al., 1998).

The PCR reactions in Eppendorf Mastercycler Personal were carried out in 50 [micro]L volume. The mixture contained 0.4 [micro]L of Hot Start Taq DNA Polymerase, 5 [micro]L of 10X Hot Start PCR Buffer, 5 [micro]L of dNTP Mix, 2 mM each, 4 [micro]L of 25 mM Mg[Cl.sub.2], 0.75 [micro]L of Bovine Serum Albumin 20 mg/mL (all reagents from Fermentas, Lithuania), 1 [micro]L of each 25 [micro]M primer (OPERON Biotechnologies, Germany), 30.85 [micro]L of sterile distilled water, and 1 [micro]L of DNA template. The polymerase chain reaction (PCR) conditions were as follows: the initial denaturation step of 4 min at 95 [degrees]C, 40 s of denaturation at 95 [degrees]C, 40 s of annealing at 52 [degrees]C, 1 min of primer extension at 72 [degrees]C (30 cycles), and final extension 10 min at 72 [degrees]C.

For ARDRA analysis with restriction endonuclease BsuRI (Chabrerie et al., 2003) the amplification products after the PCR were precipitated by 450 [micro]L of 90% ethanol and 0.3 M sodium acetate (pH 5.0). The precipitated DNA was washed with 70% ethanol, air dried, dissolved in dd[H.sub.2]O, and digested with BsuRI (Fermentas, Lithuania). Restriction fragments were visualized in native 6% polyacrylamide gel electrophoresis using a Mighty Small[TM] II (Hoefer, USA) unit. Gels were stained with ethidium bromide, photographed, and analysed with the software KODAK1D. For the calculation of the Shannon-Weaver diversity index (H') the following equation was used: H' = -[summation][p.sub.j][log.sub.2][p.sub.j], where [p.sub.j] denotes relative intensity of an individual band (Gabor et al., 2003).

Sequencing of ribosomal DNA

A total of 221 isolates (88 sporulating and 133 white or black sterile mycelia, i.e. not sporulating when kept at + 4 [degrees]C for several months) representing dominant filamentous fungi were isolated from the plates used for the enumeration of CFF and subcultured on MEA. Genomic DNA from approximately 0.25 g of mycelia was extracted using the method developed by Cenis (1992). The extracted DNA was amplified by PCR with primers ITS4 and ITS1F. The amplified DNA fragments from fungal isolates (101) from aspen stands in Kalsnava and Ukri were sequenced in CBS KNAW Fungal Biodiversity Centre, Utrecht, the Netherlands, in the frame of the project EMbaRC. After PCR 5 [micro]L of each amplified product was subjected to a sequencing protocol with BigDye Terminator Cycle Sequencing Kit (version 3.1, Applied Biosystems, USA) with both primers at CBS and only with primer ITS1F in Latvia. The sequencing of the samples from Iecava and Ropazi was performed at the Latvian Biomedical Research and Study Center. Double stranded sequences of PCR amplicons were assembled using Staden Package 1.6.0. Homology search was done against the National Centre for Biotechnology Information GenBank nucleotide database using the Basic Local Alignment Search Tool or against the Q-bank database (www.q-bank.eu).

Taxonomic data based on sequenced ribosomal DNA ITS regions of the isolates were used to calculate Sorensen's community similarity index [C.sub.s] using the following equation: [C.sub.s] = 2C/A + B, in which A and B are the number of species in samples A and B, respectively, and C is the number of species shared by the two samples (Izzo et al., 2006).

Statistical analyses

The .F-test, Z-test ([alpha] = 0.05), and correlation analysis were made with Excel (Microsoft, USA). The microbiological data (number of CFU of fungi and bacteria, total soil DNA amount, as well as the results of ARDRA) were analysed for every geographical location separately; for example, the data from the hybrid aspen stand in Kalsnava were compared with the data from the European aspen in Kalsnava. The ten soil samples were treated as one data set (n = 10).

Multiple regression analysis was made with the R package (R Development Core Team, 2009). In the regression models stands of European aspen were labelled with 0 and stands of hybrid aspens with 1. Since soil chemical analyses were made only for four soil samples from each geographical location, average values of microbiological data of 10 samples from the same soil depth were used in multiple regression analysis (n = 4). Due to co-linearity of total nitrogen and total carbon values C/N ratios were used in the regression models.

RESULTS AND DISCUSSION

Physical and chemical characterization of soil

Data on the element content, total nitrogen content, and soil pH at both analysed depths of all soil profiles are listed in Table 2. Information on soil texture and moisture content is given in Table 3. The European aspen and hybrid aspen stands in Iecava are growing on soil that is chemically and granulometrically different from the soils of all other geographically distinct sampling plots. The upper soil layers down to 30 cm contained organic material, the soil there had the highest calcium content (39.30-71.32 g [kg.sup.-1] versus 0.19-7.48 g [kg.sup.-1] in other sampling plots) and the highest total carbon content (350.8-380.4 g [kg.sup.-1] versus 10.8-39.0 g [kg.sup.-1] in other places). In several cases the level of a particular element was reduced in the soil samples from hybrid aspen in comparison to the soil samples from European aspen (Table 2). For example, total nitrogen content and potassium content were reduced in all sampling plots except in Iecava. An increased C/N ratio in the soil of the hybrid aspen stand was observed only in Kalsnava, probably due to the age of this stand. This is in line with other investigations showing that hybrid aspen litter has an increased C/N ratio in comparison to European aspen litter (Nikula et al., 2009) followed by carbon sequestration in the soil (Baum et al., 2009).

Analysis of culturable microorganisms

The count of culturable microorganisms on three microbial media is given in Fig. 2a-e. The following statistically significant differences between the soils of hybrid aspen and European aspen stands were detected: a significantly higher number of bacterial CFU on TSA in the European aspen stand at Kalsnava (F = 1.13, p = 0.02; 2.14 x [10.sup.6] CFU [g.sup.-1] of dry soil versus 1.56 x [10.sup.6] CFU [g.sup.-1] of dry soil), significantly higher numbers of yeasts and maltose utilizing bacteria on MEA in the European aspen stand at Kalsnava (F = 1.52, p = 0.003; 4.86 x [10.sup.6] CFU [g.sup.-1] of dry soil versus 1.80 x [10.sup.6] CFU [g.sup.-1] of dry soil), and significantly higher numbers of filamentous fungi CFU on MEA at a depth of 16-30 cm in the soil of the hybrid aspen clones at Ropazi (F = 12.27, p = 0.007; 6.41 x [10.sup.4] CFU [g.sup.-1] of dry soil versus 3.23 x [10.sup.4] CFU [g.sup.-1] of dry soil).

[FIGURE 2 OMITTED]

The total number of soil bacteria fluctuated from 5.37 to 6.99 log CFU [g.sup.-1] of dry soil, which is similar to the total number of bacteria in agricultural soils, where it ranges from 5.10 to 7.85 log CFU [g.sup.-1] of dry soil (Grantina et al., 2011a). The number of yeasts and maltose utilizing bacteria on MEA ranged from 5.34 to 6.71 log CFU [g.sup.-1] of dry soil and the total number of CFF was from 3.93 to 5.92 log CFU [g.sup.-1] of dry soil. These numbers are on average slightly higher than in agricultural soil where they fluctuate from 3.72 to 6.14 log CFU [g.sup.-1] of dry soil and from 2.53 to 4.89 log CFU [g.sup.-1] of dry soil, respectively (Grantina et al., 2011a), being more similar to forest soils where the level of CFF is 3.24-5.59 log CFU [g.sup.-1] of dry soil in spruce forest (Grantina et al., 2012) and 3.58-5.08 log CFU [g.sup.-1] of dry soil in mixed and pine forests (Grantina et al., 2011b).

In general the estimated CFU values represent the minimal number for CFF, because the method does not differentiate between colonies formed by single fungal spores and colonies formed by multicellular pieces of mycelium (Matthies et al., 1997). Moreover, as only a small number of bacteria (Torsvik et al., 1996) and fungi (Bridge & Spooner, 2001) are culturable, we used molecular biology methods to target also unculturable microbial populations.

Taxonomic analysis of soil fungal populations

According to the plate count method, the dominant genera of filamentous fungi were Penicillium, Trichoderma, Paecilomyces, Mortierella, and Mucor (Table 4). No statistically significant differences were observed between the soils of hybrid aspen and European aspen stands. Probably the reason was the fluctuation of results among 10 samples from the same plot and the same soil depth (Table 4). The members of the Penicillium genus ranged from 10.38% to 40.83% on RBA and from 13.04 to 45.80% on MEA (Table 4). Mortierella spp. constituted from zero to 14.89% on RBA and from 0.05% to 18.30% on MEA. Representatives of the Trichoderma genus ranged from 0.16% to 12.47% on RBA and from zero to 13.49% on MEA. The variation in the abundance of Paecilomyces spp. was from zero to 35.65% on RBA and from zero to 40.73% on MEA. The abundance of Mucor spp. varied from 0.33% to 9.36% on RBA and from 0.02% to 19.88% on MEA. Representatives of these five dominant genera constituted from 26.81% to 65.60% of all culturable fungi on RBA and from 20.34% to 82.13% on MEA. Less abundant genera were Talaromyces, Umbelopsis, Metarhizium, Beauveria, and Acremonium. Sterile white and black mycelia were observed as well.

The list of fungal genera determined according to morphological characters or sequencing results is given in Table 5. From 221 isolates sequenced 93.66% were Ascomycota (representing 58 genera), 4.98% Zygomycota (three genera), and only 1.36% Basidiomycota (one genus); all these together included 95 species. The largest part of the fungi were saprophytic: Acremonium felinum, Acremonium strictum (Watanabe, 2002), Cladosporium cladosporioides, Mucor hiemalis, Paecilomyces carneus, Penicillium montanense (Jayasinghe & Parkinson, 2008), Penicillium spp. (Baldrian et al., 2011), etc. Several identified species are entomopathogenic according to the literature: Beauveria geodes, Tolypocladium geodes (Santos et al., 2011), Metarhizium anisopliae (Leger et al., 1992), Paecilomyces carneus, P. marquandii (Sevim et al., 2010), Isaria fumosorosea (Ayala-Zermeno et al., 2011), Lecanicillium kalimantanense (Sukarno et al., 2009). Bionectria ochroleuca is associated with soil mites (Renker et al., 2005). Certain species are characterized as plant pathogens: Gibberella pulicaris (Desjardins & Gardner, 1991), Leptosphaeria sp. (Pedras, 2011), Neonectria radicicola (Halleen et al., 2004), or pathogens of soil nematodes: Plectosphaerella cucumerina (Atkins et al., 2003). Several species are associated with aspen leaves and roots: Sagenomella diversispora (Samson et al., 2011), Lophiostoma sp. (Albrectsen et al., 2010), or soil of aspen stands: Trichoderma rossicum (Friedl & Druzhinina, 2012). Fourteen species were detected in the investigation of microfungal communities of white spruce (Picea glauca (Moench) Voss) and trembling aspen (P. tremuloides Michx.) logs at different stages of decay in disturbed and undisturbed sites in boreal mixedwood forests of Alberta, Canada (Lumley et al., 2001) (last column in Table 5). Several species have been recorded to be associated with other tree species than aspens. For example, Neonectria macrodidyma was isolated as a root pathogen from the roots of nursery cultivated Pinus sylvestris L. (Menkis & Burokiene, 2012). Six species have been isolated in the rhizosphere of Salix spp.; these include Humicola fuscoatra, Mortierella alpina, Volutella ciliata, Penicillium janthinellum, and Plectosphaerella cucumerina. The abundance of the last two species correlates with the acid-phosphatase and arylsulphatase activity in the rhizosphere and is so related with the phosphorus and sulphur cycle in the soil (Baum & Hrynkiewicz, 2006). Several species have been isolated from the soil of boreal mixedwood forests in Canada (P. janthinellum, Trichoderma hamatum, T. koningii, Geomyces pannorum, M. hiemalis, P. carneus (De Bellis et al., 2007)) and/or in the soil of birch stands in central Finland (M. hiemalis, Paecilomyces carneus, and Penicillium montanense (McLean & Huhta, 2002)).

The most common fungal species in the list of sequenced isolates was Penicillium canescens with a total of 26 isolates (11.76% of all sequenced isolates). This particular species has not been detected in the other investigations of forest soil microflora mentioned in the previous paragraph. Together with other Penicillium species (40 isolates in total) this genus constituted 18.10% of the sequenced isolates. These results are in line with the results of the plate count, where the most abundant genus was Penicillium. Other common genera were Paecilomyces (15 isolates) and Hypocrea/Trichoderma (13 isolates) in all sampling plots, Acremonium (11 isolates, all from the sampling plots in Kalsnava and Ukri), Mortierella (10 isolates, in all sampling plots), Gibellulopsis (10 isolates, isolated as black sterile mycelia only in the sampling plots in Iecava and Ropazi), and Leptosphaeria (8 isolates, isolated as grey sterile mycelia in Kalsnava, Ukri, and Iecava).

Sorensen's community similarity indices [C.sub.s] between each plot of hybrid aspen and European aspen are given in Table 6. The highest Sorensen's community similarity index between soil samples of the hybrid aspen stand and the European aspen stand was at Ukri--0.39, in other sampling plots it ranged from 0.21 to 0.26. Indices [C.sub.s] among all sampling plots were lower: from 0.07 (nearly complete dissimilarity between Ropazi and Kalsnava) to 0.22 (between Ukri and Kalsnava) (Table 7). The value of [C.sub.s] between the fungal populations of all hybrid aspen stands and all European aspen stands is 0.29 (21 shared species from 68 species of hybrid aspen stands and 78 species from European aspen stands).

All calculated Sorensen's indices revealed that the fungal populations in the analysed sampling plots were quite different from one another. This is in line with an investigation in Lithuania about fungal populations in the soil of seven polluted sites, where the highest value of Sorensen's indices was 0.37 although the total number of identified species was 158 (Peciulyte & Dirginciute-Volodkiene, 2010).

Microbial diversity in soil based on ARDRA analysis

The amount of soil total DNA varied remarkably among sampling plots. The lowest amount of extracted DNA was in the sampling plots at Kalsnava and the highest amount was in the soil samples from Iecava (Fig. 3). Diversity indices calculated from the ARDRA data are given in Fig. 4. There were no statistically significant differences in the fungal and bacterial diversity between the two soil depths. For further statistical analyses the data from both soil depths were combined, but there were no significant differences in microbial diversity between the soil in the stands of hybrid aspen and the soil in the stands of European aspen. The only difference that approached the statistical significance was observed in the case of Ropazi: the average fungal diversity index H was 2.33 in the hybrid aspen stand versus 2.01 in the European aspen stand (F = 1.27; p = 0.08). In this sampling plot statistically significant differences between the number of fungal CFU on MEA were observed at a depth of [10.sup.-3]0 cm comparing the soils from the hybrid aspen and European aspen stands. It was further corroborated by statistically different fungal diversity H' values of this soil level: -2.55 versus 2.02 (F = 1.33; p = 0.03). In the case of fungal diversity versus bacterial diversity the difference among all four sampling plots was much greater than in the case of CFU numbers: significantly lower fungal diversity indices were obtained from the samples of Ukri in comparison with the samples of Iecava.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

Multiple regression analyses of the impact of soil chemical characteristi[C.sub.s] on the microbial abundance and diversity

Considering that according to the t-test there were only a few statistically significant differences between the soil microbial populations of hybrid aspen and European aspen stands, soil chemical variables were included in multiple regression models in order to determine what parameters in general have a significant impact on the analysed soil microorganisms and on the amount of total soil DNA. The results of multiple regression analyses are summarized in Table 8. As it was detected with the t-test, the aspen type significantly affected the number of filamentous fungi on MEA but not the total number of bacteria on TSA. Although the soil pH values were similar in all sampling plots, the regression models showed that soil pH significantly influenced the number of filamentous fungi on MEA and RBA, and fungal and bacterial diversity indices H'. Of all the soil variables the most important were the C/N ratio and humic acid content. The C/N ratio values ranged from 13 to 23, and higher values of this ratio correlated with lower values of several microbiological variables such as the total number of bacteria on TSA, the number of filamentous fungi on MEA, the total amount of soil DNA, and fungal diversity. The concentration of humic acids in the soil negatively influenced the number of yeasts, maltose utilizing bacteria, and filamentous fungi on MEA, the number of yeasts and fungi on RBA, and the total amount of soil DNA. A similar regularity of the occurrence of a smaller number of yeasts in the soil layers with more humus was observed in the investigation of Priha et al. (2001) of soil microbial populations in pine, spruce, and birch stands in Finland.

CONCLUSIONS

1. In general, only a minor effect of hybrid aspen on soil microbial communities was observed. Our results show that during long cultivation periods (more than 40 years as in the case of the sampling plot at Kalsnava) hybrid aspens reduce the number of culturable bacteria, probably due to the increased C/N ratio in the soil. The number of culturable filamentous fungi was significantly increased only in one sampling plot (Ropazi) of hybrid aspen in the soil sampled at a depth of 16-30 cm and only on one microbiological cultivation medium. The same trend in the fungal diversity was detected in the same sampling plot also with molecular methods estimated by Shannon-Weaver diversity indices.

2. Hybrid aspen stands did not affect any other analysed characteristi[C.sub.s] of the soil microbial population, such as the number of yeasts and maltose utilizing bacteria on MEA, the number of yeasts and filamentous fungi on RBA, the total amount of soil DNA, the fungal and bacterial diversity estimated by the methods of molecular geneti[C.sub.s], and species composition of filamentous fungi. So it is safe to cultivate hybrid aspen (Populus tremuloides Michx. x P. tremula L.) as a short rotation forest tree species in the Baltic region if the abundance and diversity of saprophytic soil microorganisms is considered.

doi: 10.3176/eco.2012.4.03

ACKNOWLEDGEMENTS

This study was supported by the project 'Capacity building for interdisciplinary biosafety research' No. 2009/0224/1DP/1.1.1.2.0/09/ APIA/VIAA/055 co-funded by the European Social Fund.

We are very thankful to the colleagues at CBS KNAW Fungal Biodiversity Centre, Utrecht, the Netherlands, and the project EMbaRC for the sequencing of fungal isolates from Kalsnava and Ukri.

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Lelde Grantina-Ievina (a) ([mail]), Dace Saulite (a), Martins Zeps (b), Vizma Nikolajeva (a), and Nils Rostoks (a)

(a) Department of Microbiology and Biotechnology, Faculty of Biology, University of Latvia, 4 Kronvalda Blvd., Riga, LV-1586, Latvia

(b) Forest Tree Breeding Group, Latvian State Forest Research Institute 'Silava', 111 Rigas Str., Salaspils, LV-2169, Latvia

([mail]) Corresponding author, lelde.grantina-ievina@lu.lv

Received 22 June 2012, revised 1 October 2012, accepted 1 October 2012
Table 1. Characterization of the sampled aspen stands

Location            Year of planting and productivity
                    Hybrid aspen      European aspen

Forest Research     1964 (a)          1966 (a)
  Station
  'Kalsnava',
  Kalsnava
  municipality

Forest Research     2000; 87          2000; 39
  Station 'Auce',   [m.sup.3]         [m.sup.3]
  Ukri              [ha.sup.-1] (b)   [ha.sup.-1] (b)
  municipality
Privately owned     1998; 215         1998; 60
  land, Iecava      [m.sup.3]         [m.sup.3]
  municipality      [ha.sup.-1] (b)   [ha.sup.-1] (b)
Privately owned     2001 (c)          2001 (c)
  land, Ropazi
  municipality

Location            Characterization         Time of
                                          soil sampling

Forest Research     Hybrid aspen          23.08.2010
  Station             (1.1 ha) and
  'Kalsnava',         European aspen
  Kalsnava            (1.1 ha) in
  municipality        separate stands.
                      Every five years
                      offshoots are cut
                      out
Forest Research     In parcels (5 x 5     15.09.2010
  Station 'Auce',     trees), 1100
  Ukri                trees [ha.sup.-1]
  municipality
Privately owned     In parcels (3 x 5     30.08.2011
  land, Iecava        trees), 2500
  municipality        trees [ha.sup.-1]
Privately owned     In parcels (5 x 5     11.10.2011
  land, Ropazi        trees), 1100
  municipality        trees [ha.sup.-1]
                      European aspen
                      clones were
                      triploid

(a) These data are not comparable due to the management activities
that include tree crown forming.

(b) Average productivity estimated at the age of 12 years.

(c) Not estimated yet.

Table 2. Element content, C/N ratio, the content of humic acids
(n = 3), and soil pH at both analysed depths in all experimental
plots. Asterisks
indicate statistically significant differences between the soil
samples from hybrid aspen (HA) and European aspen (EA) stands or
parcels at the respective depths

Plot & depth,           Ca, g                    Mg, g
cm                   [kg.sup.-1]              [kg.sup.-1]

Kalsnava, HA
  0-15          7.48 [+ or -] 0.505 *    1.53 [+ or -] 0.103
  16-30         0.19 [+ or -] 0.013 *    0.95 [+ or -] 0.064 *
Kalsnava, EA
  0-15          0.47 [+ or -] 0.032 *    1.69 [+ or -] 0.114
  16-30         0.63 [+ or -] 0.043 *    1.64 [+ or -] 0.111 *
Ukri, HA
  0-15          0.59 [+ or -] 0.040 *    2.10 [+ or -] 0.142 *
  16-30         0.56 [+ or -] 0.038 *    2.31 [+ or -] 0.156
Ukri, EA
  0-15          1.49 [+ or -] 0.101 *    2.84 [+ or -] 0.192 *
  16-30         1.10 [+ or -] 0.074 *    2.21 [+ or -] 0.149
Iecava, HA
  0-15          70.43 [+ or -] 4.757 *   3.79 [+ or -] 0.256 *
  16-30         71.32 [+ or -] 4.817     3.98 [+ or -] 0.269
Iecava, EA
  0-15          39.30 [+ or -] 2.654 *   3.26 [+ or -] 0.220 *
  16-30         68.10 [+ or -] 4.599     3.75 [+ or -] 0.253
Ropazi, HA
  0-15          0.30 [+ or -] 0.020 *    0.35 [+ or -] 0.024 *
  16-30         0.41 [+ or -] 0.028 *    0.36 [+ or -] 0.024 *
Ropazi, EA
  0-15          0.79 [+ or -] 0.053 *    0.84 [+ or -] 0.057 *
  16-30         0.38 [+ or -] 0.026 *    0.51 [+ or -] 0.034 *

Plot & depth,           K, g               [C.sub.total], g
cm                   [kg.sup.-1]              [kg.sup.-1]

Kalsnava, HA
  0-15          0.42 [+ or -] 0.019 *    21.4 [+ or -] 1.6 *
  16-30         0.50 [+ or -] 0.023 *    19.5 [+ or -] 0.7
Kalsnava, EA
  0-15          0.82 [+ or -] 0.037 *    31.3 [+ or -] 0.6 *
  16-30         0.68 [+ or -] 0.031 *    20.6 [+ or -] 0.2
Ukri, HA
  0-15          2.49 [+ or -] 0.114 *    20.3 [+ or -] 1.2 *
  16-30         4.02 [+ or -] 0.183 *    10.8 [+ or -] 0.4 *
Ukri, EA
  0-15          1.78 [+ or -] 0.081 *    39.00 [+ or -] 3.3 *
  16-30         2.10 [+ or -] 0.096 *    29.00 [+ or -] 0.3 *
Iecava, HA
  0-15          0.52 [+ or -] 0.024      380.2 [+ or -] 3.90 *
  16-30         0.56 [+ or -] 0.026      364.4 [+ or -] 3.70 *
Iecava, EA
  0-15          0.51 [+ or -] 0.023      350.8 [+ or -] 1.7 *
  16-30         0.56 [+ or -] 0.026      370.2 [+ or -] 1.2 *
Ropazi, HA
  0-15          0.41 [+ or -] 0.019 *    18.3 [+ or -] 0.6 *
  16-30         0.40 [+ or -] 0.018 *    15.1 [+ or -] 0.4 *
Ropazi, EA
  0-15          0.87 [+ or -] 0.040 *    35.6 [+ or -] 3.2 *
  16-30         0.46 [+ or -] 0.021 *    27.3 [+ or -] 1.2 *

Plot & depth,           P, g                [N.sub.total], g       C/N
cm                   [kg.sup.-1]              [kg.sup.-1]         ratio

Kalsnava, HA
  0-15          0.22 [+ or -] 0.04       1.0 [+ or -] 0.10 *       21
  16-30         0.19 [+ or -] 0.03       0.8 [+ or -] 0.00 *       23
Kalsnava, EA
  0-15          0.17 [+ or -] 0.03       1.7 [+ or -] 0.00 *       19
  16-30         0.16 [+ or -] 0.03       1.2 [+ or -] 0.00 *       17
Ukri, HA
  0-15          0.12 [+ or -] 0.02 *     1.3 [+ or -] 0.10 *       15
  16-30         0.12 [+ or -] 0.02 *     0.8 [+ or -] 0.00 *       13
Ukri, EA
  0-15          0.18 [+ or -] 0.03 *     2.7 [+ or -] 0.10 *       14
  16-30         0.17 [+ or -] 0.02 *     2.1 [+ or -] 0.10 *       14
Iecava, HA
  0-15          0.36 [+ or -] 0.06       22.1 [+ or -] 1.50        17
  16-30         0.35 [+ or -] 0.06       23.3 [+ or -] 0.40        16
Iecava, EA
  0-15          0.35 [+ or -] 0.06       22.1 [+ or -] 1.60        16
  16-30         0.33 [+ or -] 0.06       22.4 [+ or -] 2.70        17
Ropazi, HA
  0-15          0.10 [+ or -] 0.02 *     1.4 [+ or -] 0.10 *       13
  16-30         0.11 [+ or -] 0.02 *     1.0 [+ or -] 0.00 *       15
Ropazi, EA
  0-15          0.23 [+ or -] 0.05 *     2.2 [+ or -] 0.20*        16
  16-30         0.19 [+ or -] 0.04 *     1.7 [+ or -] 0.10*        16

Plot & depth,        Humic acids,             [pH.sub.H2O]
cm                   [kg.sup.-1]

Kalsnava, HA
  0-15          13.15 [+ or -] 0.01 *    6.62 [+ or -] 0.44
  16-30         36.29 [+ or -] 0.02 *    6.03 [+ or -] 0.16
Kalsnava, EA
  0-15          20.33 [+ or -] 2.69 *    6.70 [+ or -] 0.21
  16-30         24.57 [+ or -] 2.06 *    6.31 [+ or -] 0.64
Ukri, HA
  0-15          50.66 [+ or -] 0.75 *    7.12 [+ or -] 0.07
  16-30         75.72 [+ or -] 9.64 *    6.97 [+ or -] 0.28
Ukri, EA
  0-15          43.14 [+ or -] 2.01 *    7.01 [+ or -] 0.37
  16-30         47.81 [+ or -] 1.84 *    7.12 [+ or -] 0.19
Iecava, HA
  0-15          71.99 [+ or -] 8.20      6.51 [+ or -] 0.13
  16-30         73.88 [+ or -] 23.26     6.69 [+ or -] 0.09
Iecava, EA
  0-15          73.86 [+ or -] 12.75     6.65 [+ or -] 0.24
  16-30         77.30 [+ or -] 7.65      6.69 [+ or -] 0.25
Ropazi, HA
  0-15          15.88 [+ or -] 0.24      6.23 [+ or -] 0.08
  16-30         15.51 [+ or -] 1.31 *    6.08 [+ or -] 0.23
Ropazi, EA
  0-15          26.36 [+ or -] 11.78     6.75 [+ or -] 0.40
  16-30         20.08 [+ or -] 0.34 *    6.29 [+ or -] 0.19

Table 3. Granulometric content (n = 3), soil texture class and soil
moisture content (n = 10) at both analysed depths in all
experimental plots. Asterisks indicate statistically significant
differences between the soil samples from hybrid aspen (HA) and
European aspen (EA) stands or parcels at the respective depths

Plot & depth,         Clay, %               Silt, %
cm

Kalsnava, HA
  0-15          3.1 [+ or -] 0.1 *    19.3 [+ or -] 0.9 *
  16-30         4.9 [+ or -] 0.2 *    23.6 [+ or -] 1.1 *
Kalsnava, EA
  0-15          8.9 [+ or -] 0.4 *    25.0 [+ or -] 1.1 *
  16-30         8.1 [+ or -] 0.3 *    28.2 [+ or -] 1.3 *
Ukri, HA
  0-15          17.2 [+ or -] 0.7     28.3 [+ or -] 1.3
  16-30         24.7 [+ or -] 1.0 *   28.5 [+ or -] 1.3
Ukri, EA
  0-15          17.5 [+ or -] 0.7     28.7 [+ or -] 1.3
  16-30         15.8 [+ or -] 0.6 *   31.7 [+ or -] 1.4
Iecava, HA
  0-15                -- (a)                  --
  16-30                 --                    --
Iecava, EA
  0-15                  --                    --
  16-30                 --                    --
Ropazi, HA
  0-15          2.8 [+ or -] 0.1 *    18.9 [+ or -] 0.9 *
  16-30         1.9 [+ or -] 0.1 *    18.3 [+ or -] 0.8 *
Ropazi, EA
  0-15          4.5 [+ or -] 0.2 *    24.4 [+ or -] 1.1 *
  16-30         4.5 [+ or -] 0.2 *    23.0 [+ or -] 1.0 *

Plot & depth,         Sand, %         Soil texture
cm                                       class

Kalsnava, HA
  0-15          77.6 [+ or -]2.1 *     Loamy sand
  16-30         71.4 [+ or -] 1.9 *    Sandy loam
Kalsnava, EA
  0-15          66.1 [+ or -] 1.8 *    Sandy loam
  16-30         63.8 [+ or -] 1.7 *    Sandy loam
Ukri, HA
  0-15          54.4 [+ or -] 1.5      Sandy loam
  16-30         46.7 [+ or -] 1.3 *       Loam
Ukri, EA
  0-15          53.8 [+ or -] 1.4      Sandy loam
  16-30         52.5 [+ or -] 1.4 *    Sandy loam
Iecava, HA
  0-15                  --                 --
  16-30                 --                 --
Iecava, EA
  0-15                  --                 --
  16-30                 --                 --
Ropazi, HA
  0-15          78.3 [+ or -] 2.1 *    Loamy sand
  16-30         79.8 [+ or -] 2.2 *    Loamy sand
Ropazi, EA
  0-15          71.0 [+ or -] 1.9*     Sandy loam
  16-30         72.5 [+ or -] 2.0*     Sandy loam

Plot & depth,      Soil moisture
cm                   content, %

Kalsnava, HA
  0-15          25.74 [+ or -] 12.07
  16-30         26.95 [+ or -] 12.65
Kalsnava, EA
  0-15          21.72 [+ or -] 2.07
  16-30         17.30 [+ or -] 1.94
Ukri, HA
  0-15          15.61 [+ or -] 7.58
  16-30         12.27 [+ or -] 2.45
Ukri, EA
  0-15          24.96 [+ or -] 19.48
  16-30         14.57 [+ or -] 2.97
Iecava, HA
  0-15          50.06 [+ or -] 3.85
  16-30         49.28 [+ or -] 7.02
Iecava, EA
  0-15          51.85 [+ or -] 3.86
  16-30         52.75 [+ or -] 3.85
Ropazi, HA
  0-15          22.49 [+ or -] 2.50
  16-30         16.32 [+ or -] 1.98
Ropazi, EA
  0-15          25.37 [+ or -] 8.39
  16-30         16.66 [+ or -] 4.85

(a) The soil of these sampling plots was drained peat soil that
contained only organic material
at a depth of 0-30 cm.

Table 4. Average percentage of the representatives of five dominant
fungal genera in the experimental
plots (number of soil samples from each depth n = 10)

Experimental       Depth,   Penicillium     Mortierella
plot               cm       spp., %         spp., %
                             RBA     MEA     RBA     MEA

Kalsnava,           0-15    40.83   25.46    0.00    0.68
  European aspen   16-30    32.47   40.34    5.41    8.42
Kalsnava, hybrid    0-15    37.78   19.15    0.87    9.31
  aspen            16-30    24.25   13.56    0.15    3.39
Ukri, European      0-15    19.97   36.39    4.24    8.16
  aspen            16-30    20.01   45.34   13.63    0.05
Ukri, hybrid        0-15    30.62   29.88   14.89    1.36
  aspen            16-30    12.04   32.86    0.88    9.28
Iecava, European    0-15    24.76   14.37    5.87   18.30
  aspen            16-30    16.05   32.59   10.95   10.01
Iecava, hybrid      0-15    22.42   14.52    4.32    0.62
  aspen            16-30    25.44   20.73    2.57    6.79
Ropazi, European    0-15    29.45   37.14    5.86    0.98
  aspen            16-30    32.73   13.04    1.86   10.48
Ropazi, hybrid      0-15    19.69   45.80    4.99    7.19
  aspen            16-30    10.38   17.22   10.30    5.06

Experimental       Trichoderma     Paecilomyces    Mucor
plot               spp., %         spp., %         spp., %
                    RBA     MEA     RBA     MEA     RBA     MEA

Kalsnava,           8.22   6.74    4.68    40.73   1.14    1.15
  European aspen    1.71   13.49   11.85   0.00    0.33    19.88
Kalsnava, hybrid    0.65   0.71    0.00    38.14   1.18    0.68
  aspen             0.16   0.00    0.00    0.00    2.25    3.39
Ukri, European      1.21   7.53    12.78   0.00    0.43    0.25
  aspen             1.70   0.05    4.95    0.00    1.73    0.82
Ukri, hybrid        1.14   1.24    0.00    0.00    1.08    0.13
  aspen             1.13   2.31    35.65   0.00    3.24    0.02
Iecava, European    0.87   0.25    29.37   15.70   1.01    1.04
  aspen             0.17   2.36    3.04    8.84    1.03    1.58
Iecava, hybrid      1.21   11.53   16.93   13.38   0.97    2.30
  aspen             2.40   1.87    1.03    2.66    1.11    1.53
Ropazi, European    2.03   5.92    15.42   11.24   0.78    1.23
  aspen             4.05   1.03    17.60   0.85    9.36    2.16
Ropazi, hybrid     12.47   2.38    8.69    6.53    0.85    2.45
  aspen             9.90   3.24    1.66    31.40   0.42    1.54

Table 5. List of fungal genera determined in the soil of hybrid
aspen (HA) and European aspen (EA) stands according to morphological
characters
(indicated by x) or ribosomal DNA sequencing (indicated by total
number of isolates and GenBank accession numbers of the homologue
sequence)

Species                                      Kalsnava   Ukri
                                             HA   EA   HA   EA

Ascomycota
  Acremonium felinum (Marchai) Kiyuna,            1    3    3
An, Kigawa & Sugiy.
Acremonium strictum W. Gams                       1    2    1

Acremonium sp.                                    X
Alternaria sp.                                              1
Aporospora terricola J.C. Krug & Jeng                  1
Arthrinium sacchari (Speg.) M.B. Ellis
Aureobasidium sp.                                 1
Auxarthron umbrinum (Boud.) G.F. Orr &                      1
  Plunkett
Beauveria geodes (W. Gams) Arx                              X
Beauveria sp.                                               X
Bionectria levigata Schroers
Bionectria ochroleuca (Schwein.)
  Schroers & Samuels

Botryotinia fuckeliana (de Bary) Whetzel     1
Cadophora finlandica (C.J.K. Wang &
  H.E. Wilcox) T.C. Harr. & McNew
Cladosporium cladosporioides (Fresen.)
  G.A. de Vries
Clonostachys divergens Schroers
Dokmaia sp.                                            2    1
Emericella bicolor M. Chr. &
  States/Aspergillus bicolor M. Chr. &
  States
Emericella foeniculicola Udagawa
Eremomyces langeronii (Arx) Malloch &
  Sigler
Eucasphaeria capensis Crous                                 1

Exophiala salmonis J.W. Carmich.                  1    1    1

Fusarium merismoides var. merismoides
  Corda
Fusarium oxysporum Schltdl.                            1
Fusarium sp.                                      X
Geomyces pannorum (Link) Sigler &            1
  J.W. Carmich.
Geomyces destructans Blehert & Gargas                  1    1
Geomyces sp.                                                1
Gibber ella pulicaris (Fr.) Sacc.                           1
Gibellulopsis nigrescens (Pethybr.) Zare,
  W. Gams & Summerb.
Gliomastlx murorum (Corda) S. Hughes
Humicola fuscoatra Traaen
Humico la sp.                                     X
Hyalodendriella betulae Crous
Hypocrea koningii Lieckf., Samuels &              2
  W. Gams /Trichoderma koningii
  Oudem.
Hypocrea lixii Pat.

Hypocrea pachybasioides Yoshim. Doi          1
Hypocrea viridescens Jaklitsch &                  2
  SamueWTrichoderma viridescens
  (A.S. Home & H.S. Will.) Jaklitsch &
  Samuels
Ilyonectria europaea A. Cabral, Rego &
  Crous
Ilyonectria rufa A. Cabral & Crous
Isaria fumosorosea Wize
Kernia pachypleura Malloch & Cain
Lecanicillium kalimantanense Kurihara &
  Sukarno
Lecanicillium sp.
Leptosphaeria conferia Niessl ex Sacc.
Leptosphaeria maculans (Desm.) Ces. &
  De Not.
Leptosphaeria sp.                                 2    2
Leptospora rubella                                          1
Leucostoma persoonu (Nitschke) Hohn.
Lophiostoma sp.
Metarhizium anisopliae (Metschn.)            X    1 X       1 X
 Sorokin
Nectria lugdunensis J. Webster                    1
Nectria mariannaeae Samuels & Seifert                  1
Nectria vilior Starback
Neonectria macrodidyma Halleen,
  Schroers & Crous
Neonectria radicicola (Gerlach &                       1
  L. Nilsson) Mantiri & Samuels
Neonectria ramulariae Wollenw.

Paecilomyces carneus (Duche &                1    2
  R. Heim) A.H.S. Br. & G. Sm.

Paecilomyces marquandii (Massee)                       3    2
  S. Hughes

Paecilomyces sp.                             X    X    X    X
Paraconiothyrium sporulosum (W. Gams                   1
  & Domsch) Verkley
Penicillium brasilianum Bat.
Penicillium canescens Sopp                   2    1    7    1

Penicillium corylophilum Dierckx             1
Penicillium janthinellum Biourge                  1
Penicillium montanense M. Chr. &
  Backus
Penicillium roseopurpureum Dierckx

Penicillium swiecicikii K.M. Zalessky

Penicillium sp.                              1
Penicillium sp.                              X    X    X    X
Plectosphaerella cucumerina (Lindf.)                   2
  W. Gams
Pochonia suchlasporia (W. Gams &
  Dackman) Zare & W. Gams
Podospora appendiculata (Auersw. ex
Niessl) Niessl
Pseudallescheria fimeti (Arx, Mukerji &
  N. Singh) McGinnis, A.A. Padhye &
  Ajello
Pseudeurotium bakeri C. Booth                               1
Pyrenochaeta acicola (Moug. & Lev.)
  Sacc.
Pyrenochaeta inflorescentiae Crous,                    1
  Marine. & M.J. Wingf.
Rhizopycnis vagum D.F. Fair                  1
Sagenomella diversispora (J.F.H. Beyma)           1
  W. Gams
Scedosporium apiospermum Sacc. ex                      1
  Castell. & Chaim.
Scytalidium lignicola Pesante
Talaromyces ucrainicus Udagawa
Tetracladium setigerum (Grove) Ingold
Trichocladium asperum Harz                   1         1

Trichocladium opacum (Corda) S. Hughes                      1
Trichoderma hamatum (Bonord.) Bainier

Trichoderma rossicum Bissett,
  CP. Kubicek & Szakacs
Trichoderma tomentosum Bissett                              1
Trichoderma sp.                                   X    X    X
Verticillium dahliae Kleb.
Verticillium sp.                                  X
Volutella ciliata (Alb. & Schwein.) Fr.                1

Wardomyces inflatus (Marchai)
  Hennebert
Zalerion varium Anastasiou                   1
Zygomycota
Mortierella alpina Peyronel                  1    1

Mortierella clonocystis W. Gams
Mortierella globulifera 0. Rostr.
Mortierella sp.                                   3    1

Mortierella sp.                              X    X    X    X
Mucor hiemalis Wehmer
Mucor sp.                                    X    X    X    X
Umbelopsis sp.                               X         X
Basidiomycota
Trichosporon porosum (Stautz)
  Middelhoven, Scorzetti & Fell
Trichosporon sp.                                  2

Species                                      Iecava    Ropazi
                                             HA   EA   HA   EA

Ascomycota
  Acremonium felinum (Marchai) Kiyuna,
An, Kigawa & Sugiy.
Acremonium strictum W. Gams

Acremonium sp.
Alternaria sp.                               1         1
Aporospora terricola J.C. Krug & Jeng
Arthrinium sacchari (Speg.) M.B. Ellis                      1
Aureobasidium sp.
Auxarthron umbrinum (Boud.) G.F. Orr &
  Plunkett
Beauveria geodes (W. Gams) Arx               X    X    1
Beauveria sp.                                X    X    X    X
Bionectria levigata Schroers                 1
Bionectria ochroleuca (Schwein.)             2         1    1
  Schroers & Samuels

Botryotinia fuckeliana (de Bary) Whetzel
Cadophora finlandica (C.J.K. Wang &                    2
  H.E. Wilcox) T.C. Harr. & McNew
Cladosporium cladosporioides (Fresen.)                      1
  G.A. de Vries
Clonostachys divergens Schroers                             1
Dokmaia sp.
Emericella bicolor M. Chr. &                 1
  States/Aspergillus bicolor M. Chr. &
  States
Emericella foeniculicola Udagawa                  1
Eremomyces langeronii (Arx) Malloch &        1
  Sigler
Eucasphaeria capensis Crous                            1    2

Exophiala salmonis J.W. Carmich.                       1

Fusarium merismoides var. merismoides        1
  Corda
Fusarium oxysporum Schltdl.
Fusarium sp.                                      1
Geomyces pannorum (Link) Sigler &
  J.W. Carmich.
Geomyces destructans Blehert & Gargas
Geomyces sp.
Gibber ella pulicaris (Fr.) Sacc.
Gibellulopsis nigrescens (Pethybr.) Zare,    3    1    1    5
  W. Gams & Summerb.
Gliomastlx murorum (Corda) S. Hughes         1
Humicola fuscoatra Traaen                         1
Humico la sp.
Hyalodendriella betulae Crous                               1
Hypocrea koningii Lieckf., Samuels &
  W. Gams /Trichoderma koningii
  Oudem.
Hypocrea lixii Pat.                                    2

Hypocrea pachybasioides Yoshim. Doi
Hypocrea viridescens Jaklitsch &
  SamueWTrichoderma viridescens
  (A.S. Home & H.S. Will.) Jaklitsch &
  Samuels
Ilyonectria europaea A. Cabral, Rego &                 1    1
  Crous
Ilyonectria rufa A. Cabral & Crous                          1
Isaria fumosorosea Wize                                     1
Kernia pachypleura Malloch & Cain                           1
Lecanicillium kalimantanense Kurihara &                     1
  Sukarno
Lecanicillium sp.                                           1
Leptosphaeria conferia Niessl ex Sacc.                      1
Leptosphaeria maculans (Desm.) Ces. &             1
  De Not.
Leptosphaeria sp.                                 2
Leptospora rubella
Leucostoma persoonu (Nitschke) Hohn.         1
Lophiostoma sp.                              1
Metarhizium anisopliae (Metschn.)                 1 X       X
 Sorokin
Nectria lugdunensis J. Webster
Nectria mariannaeae Samuels & Seifert
Nectria vilior Starback                      1
Neonectria macrodidyma Halleen,                        1    1
  Schroers & Crous
Neonectria radicicola (Gerlach &
  L. Nilsson) Mantiri & Samuels
Neonectria ramulariae Wollenw.                         2

Paecilomyces carneus (Duche &                     1
  R. Heim) A.H.S. Br. & G. Sm.

Paecilomyces marquandii (Massee)             1    2    1    2
  S. Hughes

Paecilomyces sp.                             X    X    X    X
Paraconiothyrium sporulosum (W. Gams
  & Domsch) Verkley
Penicillium brasilianum Bat.                                1
Penicillium canescens Sopp                   1         7    7

Penicillium corylophilum Dierckx
Penicillium janthinellum Biourge
Penicillium montanense M. Chr. &                            1
  Backus
Penicillium roseopurpureum Dierckx           1    2

Penicillium swiecicikii K.M. Zalessky             1         3

Penicillium sp.                                        2
Penicillium sp.                              X    X    X    X
Plectosphaerella cucumerina (Lindf.)
  W. Gams
Pochonia suchlasporia (W. Gams &             1              2
  Dackman) Zare & W. Gams
Podospora appendiculata (Auersw. ex                         1
Niessl) Niessl
Pseudallescheria fimeti (Arx, Mukerji &                1
  N. Singh) McGinnis, A.A. Padhye &
  Ajello
Pseudeurotium bakeri C. Booth
Pyrenochaeta acicola (Moug. & Lev.)                         1
  Sacc.
Pyrenochaeta inflorescentiae Crous,                    1
  Marine. & M.J. Wingf.
Rhizopycnis vagum D.F. Fair
Sagenomella diversispora (J.F.H. Beyma)
  W. Gams
Scedosporium apiospermum Sacc. ex
  Castell. & Chaim.
Scytalidium lignicola Pesante                               1
Talaromyces ucrainicus Udagawa                    X    X    1 X
Tetracladium setigerum (Grove) Ingold                  1
Trichocladium asperum Harz

Trichocladium opacum (Corda) S. Hughes
Trichoderma hamatum (Bonord.) Bainier                  3

Trichoderma rossicum Bissett,                          1    1
  CP. Kubicek & Szakacs
Trichoderma tomentosum Bissett
Trichoderma sp.                              X    X    X    X
Verticillium dahliae Kleb.                   1              1
Verticillium sp.
Volutella ciliata (Alb. & Schwein.) Fr.           1

Wardomyces inflatus (Marchai)                               1
  Hennebert
Zalerion varium Anastasiou
Zygomycota
Mortierella alpina Peyronel                                 2

Mortierella clonocystis W. Gams                   1
Mortierella globulifera 0. Rostr.                      1
Mortierella sp.

Mortierella sp.                              X    X    X    X
Mucor hiemalis Wehmer                                  1
Mucor sp.                                    X    X    X    X
Umbelopsis sp.                               X              X
Basidiomycota
Trichosporon porosum (Stautz)                               1
  Middelhoven, Scorzetti & Fell
Trichosporon sp.

Species                                        Homologue      No. in
                                               sequence,     MSCL (a)
                                             NCBI acc. No.
Ascomycota
  Acremonium felinum (Marchai) Kiyuna,        AB540562.1       1058
An, Kigawa & Sugiy.
Acremonium strictum W. Gams                    U57671.1       1063,
                                                              1064,
                                                               1120
Acremonium sp.                                    --            --
Alternaria sp.                                GU934500.1
Aporospora terricola J.C. Krug & Jeng         AF049088.1        --
Arthrinium sacchari (Speg.) M.B. Ellis        EU579803.1        --
Aureobasidium sp.                             GQ906942.1       1116
Auxarthron umbrinum (Boud.) G.F. Orr &        FR718876.1        --
  Plunkett
Beauveria geodes (W. Gams) Arx                 U19037.1        1187
Beauveria sp.                                     --            --
Bionectria levigata Schroers                  AF210680.1       1202
Bionectria ochroleuca (Schwein.)              GU934503.1      1190,
  Schroers & Samuels                                          1196,
                                                               1247
Botryotinia fuckeliana (de Bary) Whetzel      HM989942.1        --
Cadophora finlandica (C.J.K. Wang &           EF093179.1      1248,
  H.E. Wilcox) T.C. Harr. & McNew                              1259
Cladosporium cladosporioides (Fresen.)        HQ832794.1        --
  G.A. de Vries
Clonostachys divergens Schroers               GU934587.1       1268
Dokmaia sp.                                   HQ631068.1       1134
Emericella bicolor M. Chr. &                  EF652511.1       1194
  States/Aspergillus bicolor M. Chr. &
  States
Emericella foeniculicola Udagawa              AB249011.1       1192
Eremomyces langeronii (Arx) Malloch &         AB128973.1       1199
  Sigler
Eucasphaeria capensis Crous                   GU934520.1      1182,
                                                              1184,
                                                               1232
Exophiala salmonis J.W. Carmich.              GU586858.1      1114,
                                                              1117,
                                                              1124,
                                                               1260
Fusarium merismoides var. merismoides         EU860057.1       1204
  Corda
Fusarium oxysporum Schltdl.                   GU445377.1       1105
Fusarium sp.                                  HQ731631.1       1199
Geomyces pannorum (Link) Sigler &             DQ189229.1       1130
  J.W. Carmich.
Geomyces destructans Blehert & Gargas         GU999986.1       1113
Geomyces sp.                                  DQ402527.1       1088
Gibber ella pulicaris (Fr.) Sacc.             FJ481029.1       1143
Gibellulopsis nigrescens (Pethybr.) Zare,     HQ115693.1      1189,
  W. Gams & Summerb.                                          1191,
Gliomastlx murorum (Corda) S. Hughes          AB540556.1       1235
Humicola fuscoatra Traaen                     AB625589.1        --
Humico la sp.                                     --            --
Hyalodendriella betulae Crous                 EU040232.1       1243
Hypocrea koningii Lieckf., Samuels &          AJ301990.1       1131
  W. Gams /Trichoderma koningii
  Oudem.
Hypocrea lixii Pat.                           AY605716.1,     1230,
                                              HQ259311.1       1245
Hypocrea pachybasioides Yoshim. Doi           GU934589.1       1127
Hypocrea viridescens Jaklitsch &              GU566274.1        --
  SamueWTrichoderma viridescens
  (A.S. Home & H.S. Will.) Jaklitsch &
  Samuels
Ilyonectria europaea A. Cabral, Rego &        JF735294.1       1241
  Crous
Ilyonectria rufa A. Cabral & Crous            JF735278.1        --
Isaria fumosorosea Wize                       JF792885.1       1239
Kernia pachypleura Malloch & Cain             DQ318208.1       1186
Lecanicillium kalimantanense Kurihara &       AB360356.1       1270
  Sukarno
Lecanicillium sp.                             AB378528.1       1242
Leptosphaeria conferia Niessl ex Sacc.        AF439459.1       1264
Leptosphaeria maculans (Desm.) Ces. &          M96663.1        1196
  De Not.
Leptosphaeria sp.                             AY336132.1      1062,
Leptospora rubella                            AF383951.1        --
Leucostoma persoonu (Nitschke) Hohn.          HM061319.1       1193
Lophiostoma sp.                               HM116744.1        --
Metarhizium anisopliae (Metschn.)             HM055436.1       1112
 Sorokin
Nectria lugdunensis J. Webster                DQ247778.1       1101
Nectria mariannaeae Samuels & Seifert         EU273515.1       1048
Nectria vilior Starback                        U57673.1        1198
Neonectria macrodidyma Halleen,               HM036602.1        --
  Schroers & Crous
Neonectria radicicola (Gerlach &              AJ875336.1       1123
  L. Nilsson) Mantiri & Samuels
Neonectria ramulariae Wollenw.                JF735314.1      1262,
                                                               1263
Paecilomyces carneus (Duche &                 AB258369.1      1140,
  R. Heim) A.H.S. Br. & G. Sm.                                1126,
                                                               1188
Paecilomyces marquandii (Massee)              AB099511.1,     1061,
  S. Hughes                                   AB114223.1,     1121,
                                              FR799470.1      1141,
                                                              1151,
                                                              1236,
                                                              1237,
                                                              1255,
                                                               1257
Paecilomyces sp.                                  --            --
Paraconiothyrium sporulosum (W. Gams          GU566257.1       1059
  & Domsch) Verkley
Penicillium brasilianum Bat.                  HM469396.1       1229
Penicillium canescens Sopp                    FJ439586.1,     1091,
                                              FJ791141.1,     1093,
                                              AY373901.1,     1095,
                                              JF311911.1      1104,
                                                              1107,
                                                              1109,
                                                              1110,
                                                              1119,
                                                               1208
                                                              1216,
                                                               1223
                                                               1227
Penicillium corylophilum Dierckx              GU566277.1       1135
Penicillium janthinellum Biourge              AB293968.1       1097
Penicillium montanense M. Chr. &              HQ157959.1       1228
  Backus
Penicillium roseopurpureum Dierckx            JF311930.1,      1218
                                              JN246027.1       1220
Penicillium swiecicikii K.M. Zalessky         AJ608946.1      1217,
                                                              1222,
                                                               1253
Penicillium sp.                               GU446648.1        --
Penicillium sp.                                   --            --
Plectosphaerella cucumerina (Lindf.)          AJ492873.1       1103
  W. Gams
Pochonia suchlasporia (W. Gams &              AB214658.1      1192,
  Dackman) Zare & W. Gams                                      1240
Podospora appendiculata (Auersw. ex           AY999126.1       1201
Niessl) Niessl
Pseudallescheria fimeti (Arx, Mukerji &       AY879799.1        --
  N. Singh) McGinnis, A.A. Padhye &
  Ajello
Pseudeurotium bakeri C. Booth                 GU934582.1       1133
Pyrenochaeta acicola (Moug. & Lev.)                            1251
  Sacc.
Pyrenochaeta inflorescentiae Crous,           GU5 86851.1      1149
  Marine. & M.J. Wingf.
Rhizopycnis vagum D.F. Fair                   HQ610506.1        --
Sagenomella diversispora (J.F.H. Beyma)       GQ169318.1       1111
  W. Gams
Scedosporium apiospermum Sacc. ex             AB567756.1       1051
  Castell. & Chaim.
Scytalidium lignicola Pesante                 FJ914697.1        --
Talaromyces ucrainicus Udagawa                AY533695.1       1231
Tetracladium setigerum (Grove) Ingold         FJ000374.1       1265
Trichocladium asperum Harz                    HQ115689.1,      1108
                                              AY706336.1
Trichocladium opacum (Corda) S. Hughes        AM292049.1       958
Trichoderma hamatum (Bonord.) Bainier         JN542526.1      1233,
                                                               1234
Trichoderma rossicum Bissett,                 DQ083024.1,     1183,
  CP. Kubicek & Szakacs                       EU280089.1       1246
Trichoderma tomentosum Bissett                AY605737.1        --
Trichoderma sp.                                   --            --
Verticillium dahliae Kleb.                    HQ839784.1       1197
Verticillium sp.                                  --            --
Volutella ciliata (Alb. & Schwein.) Fr.       GU586855.1,      1203
                                              HQ897802.1
Wardomyces inflatus (Marchai)                 FJ946485.1       1252
  Hennebert
Zalerion varium Anastasiou                    AJ608987.1       1118
Zygomycota
Mortierella alpina Peyronel                   AJ271629.1,     1098,
                                              FJ478130.1,     1254,
                                              JN943023.1       1271
Mortierella clonocystis W. Gams               HQ630318.1       1200
Mortierella globulifera 0. Rostr.             JN943800.1       1244
Mortierella sp.                               FJ810149.1,      1052
                                              FJ810151.1,
                                              DQ093725.1
Mortierella sp.                                   --            --
Mucor hiemalis Wehmer                         EU484263.1       1181
Mucor sp.                                         --            --
Umbelopsis sp.                                    --            --
Basidiomycota
Trichosporon porosum (Stautz)                 AJ608971.1        --
  Middelhoven, Scorzetti & Fell
Trichosporon sp.                              FJ439589.1        --

Species                                        Detected
                                              in Lumley
                                             et al., 2001
Ascomycota
  Acremonium felinum (Marchai) Kiyuna,            --
An, Kigawa & Sugiy.
Acremonium strictum W. Gams                       +

Acremonium sp.                                    --
Alternaria sp.                                    --
Aporospora terricola J.C. Krug & Jeng             --
Arthrinium sacchari (Speg.) M.B. Ellis            +
Aureobasidium sp.                                 --
Auxarthron umbrinum (Boud.) G.F. Orr &            --
  Plunkett
Beauveria geodes (W. Gams) Arx                    --
Beauveria sp.                                     --
Bionectria levigata Schroers                      --
Bionectria ochroleuca (Schwein.)                  --
  Schroers & Samuels

Botryotinia fuckeliana (de Bary) Whetzel          --
Cadophora finlandica (C.J.K. Wang &               --
  H.E. Wilcox) T.C. Harr. & McNew
Cladosporium cladosporioides (Fresen.)            +
  G.A. de Vries
Clonostachys divergens Schroers                   --
Dokmaia sp.                                       --
Emericella bicolor M. Chr. &                      --
  States/Aspergillus bicolor M. Chr. &
  States
Emericella foeniculicola Udagawa                  --
Eremomyces langeronii (Arx) Malloch &             --
  Sigler
Eucasphaeria capensis Crous                       --

Exophiala salmonis J.W. Carmich.                  +

Fusarium merismoides var. merismoides             --
  Corda
Fusarium oxysporum Schltdl.                       --
Fusarium sp.                                      --
Geomyces pannorum (Link) Sigler &                 +
  J.W. Carmich.
Geomyces destructans Blehert & Gargas             --
Geomyces sp.                                      --
Gibber ella pulicaris (Fr.) Sacc.                 --
Gibellulopsis nigrescens (Pethybr.) Zare,         --
  W. Gams & Summerb.
Gliomastlx murorum (Corda) S. Hughes              --
Humicola fuscoatra Traaen                         +
Humico la sp.                                     --
Hyalodendriella betulae Crous                     --
Hypocrea koningii Lieckf., Samuels &              +
  W. Gams /Trichoderma koningii
  Oudem.
Hypocrea lixii Pat.                               --

Hypocrea pachybasioides Yoshim. Doi               --
Hypocrea viridescens Jaklitsch &                  --
  SamueWTrichoderma viridescens
  (A.S. Home & H.S. Will.) Jaklitsch &
  Samuels
Ilyonectria europaea A. Cabral, Rego &            --
  Crous
Ilyonectria rufa A. Cabral & Crous                --
Isaria fumosorosea Wize                           --
Kernia pachypleura Malloch & Cain                 --
Lecanicillium kalimantanense Kurihara &           --
  Sukarno
Lecanicillium sp.                                 --
Leptosphaeria conferia Niessl ex Sacc.            --
Leptosphaeria maculans (Desm.) Ces. &             --
  De Not.
Leptosphaeria sp.                                 --
Leptospora rubella                                --
Leucostoma persoonu (Nitschke) Hohn.              --
Lophiostoma sp.                                   --
Metarhizium anisopliae (Metschn.)                 --
 Sorokin
Nectria lugdunensis J. Webster                    --
Nectria mariannaeae Samuels & Seifert             --
Nectria vilior Starback                           --
Neonectria macrodidyma Halleen,                   --
  Schroers & Crous
Neonectria radicicola (Gerlach &                  --
  L. Nilsson) Mantiri & Samuels
Neonectria ramulariae Wollenw.

Paecilomyces carneus (Duche &                     1
  R. Heim) A.H.S. Br. & G. Sm.

Paecilomyces marquandii (Massee)                  --
  S. Hughes

Paecilomyces sp.                                  --
Paraconiothyrium sporulosum (W. Gams              --
  & Domsch) Verkley
Penicillium brasilianum Bat.                      --
Penicillium canescens Sopp                        --

                                                  --

                                                  --
Penicillium corylophilum Dierckx                  --
Penicillium janthinellum Biourge                  --
Penicillium montanense M. Chr. &                  --
  Backus
Penicillium roseopurpureum Dierckx                --

Penicillium swiecicikii K.M. Zalessky             --

Penicillium sp.                                   --
Penicillium sp.                                   --
Plectosphaerella cucumerina (Lindf.)              --
  W. Gams
Pochonia suchlasporia (W. Gams &                  --
  Dackman) Zare & W. Gams
Podospora appendiculata (Auersw. ex               --
Niessl) Niessl
Pseudallescheria fimeti (Arx, Mukerji &           --
  N. Singh) McGinnis, A.A. Padhye &
  Ajello
Pseudeurotium bakeri C. Booth                     --
Pyrenochaeta acicola (Moug. & Lev.)               --
  Sacc.
Pyrenochaeta inflorescentiae Crous,               --
  Marine. & M.J. Wingf.
Rhizopycnis vagum D.F. Fair                       --
Sagenomella diversispora (J.F.H. Beyma)           --
  W. Gams
Scedosporium apiospermum Sacc. ex                 --
  Castell. & Chaim.
Scytalidium lignicola Pesante                     +
Talaromyces ucrainicus Udagawa                    --
Tetracladium setigerum (Grove) Ingold             --
Trichocladium asperum Harz                        --

Trichocladium opacum (Corda) S. Hughes            --
Trichoderma hamatum (Bonord.) Bainier             +

Trichoderma rossicum Bissett,                     --
  CP. Kubicek & Szakacs
Trichoderma tomentosum Bissett                    --
Trichoderma sp.                                   --
Verticillium dahliae Kleb.                        --
Verticillium sp.                                  --
Volutella ciliata (Alb. & Schwein.) Fr.           +

Wardomyces inflatus (Marchai)                     +
  Hennebert
Zalerion varium Anastasiou                        --
Zygomycota
Mortierella alpina Peyronel                       +

Mortierella clonocystis W. Gams                   --
Mortierella globulifera 0. Rostr.                 --
Mortierella sp.                                   --

Mortierella sp.                                   --
Mucor hiemalis Wehmer                             +
Mucor sp.                                         --
Umbelopsis sp.                                    --
Basidiomycota
Trichosporon porosum (Stautz)                     --
  Middelhoven, Scorzetti & Fell
Trichosporon sp.                                  --

(a) Microbial Strain Collection of Latvia.

* According to the Q-bank database.

Table 6. Total number of fungal species, number of shared species,
and values of Sorensen's community similarity indices [C.sub.s]
between each plot of hybrid aspen (HA) and European aspen (EA)

Sampling plot    Kalsnava        Ukri         Iecava        Ropazi
(total number     HA (12)       HA (19)       HA (14)       HA (23)
of species)

Kalsnava EA      [C.sub.s]
(15)              = 0.22
                  (3 shared
                  species)
Ukri EA                        [C.sub.s]
(17)                            = 0.39
                                (7 shared
                                species)
Iecava EA                                    [C.sub.s]
(15)                                          = 0.21
                                              (3 shared
                                              species)
Ropazi EA                                                  [C.sub.s]
(31)                                                        = 0.26
                                                            (7 shared
                                                            species)

Table 7. Total number of fungal species, number of shared species,
and values of Sorensen's community similarity indices [C.sub.s] among
all sampling plots

Sampling plot    Ukri (36)    Iecava (29)   Ropazi (54)
(total number
of species)

Kalsnava (27)   [C.sub.s]     [C.sub.s]     [C.sub.s]
                  = 0.22        = 0.14        = 0.07
                  (7 shared     (4 shared     (3 shared
                  species)      species)      species)
Ukri (36)                     [C.sub.s]     [C.sub.s]
                                = 0.18        = 0.11
                                (6 shared     (5 shared
                                species)      species)
Iecava (29)                                 [C.sub.s]
                                              = 0.19
                                              (8 shared
                                              species)

Table 8. Results of multiple regression analyses (p-values)

Factor                  Total number      Yeasts and
                        of bacteria    maltose utilizing
                           on TSA       bacteria on MEA

Soil sampling depth      <0.0001 (a)          NS
Aspen type                   NS               NS
Soil moisture content        NS            <0.0001
Soil pH                      NS               NS
Calcium content              NS               NS
Magnesium content         0.0006              NS
Potassium content         0.0004 (a)          NS
Phosphorus content        0.02 (a)            NS
C/N ratio                 0.002 (a)           NS
Humic acids                  NS             0.004 (a)
Multiple [R.sup.2]        0.90              0.74
p-Value of the model      0.0001            0.0002

Factor                  Filamentous       Yeasts      Filamentous
                        fungi on MEA      on RBA      fungi on RBA

Soil sampling depth          NS             NS             NS
Aspen type                 0.0005           NS             NS
Soil moisture content      0.0007        <0.0001         0.0005
Soil pH                    0.002            NS           0.02
Calcium content              NS             NS             NS
Magnesium content            NS             NS           0.003 (a)
Potassium content            NS             NS           0.01
Phosphorus content           NS             NS           0.046 (a)
C/N ratio                  0.04 (a)         NS           0.002
Humic acids               <0.0001 (a)    <0.004 (a)      0.006 (a)
Multiple [R.sup.2]         0.87           0.74           0.94
p-Value of the model       0.0003         0.0002         0.001

Factor                  Total amount      Fungal        Bacterial
                        of soil DNA     diversity,     diversity,
                                            H'             H'

Soil sampling depth          NS             NS             NS
Aspen type                   NS             NS             NS
Soil moisture content     <0.0001        <0.0001           NS
Soil pH                      NS          <0.0001 (a)     0.02
Calcium content              NS             NS          <0.0001
Magnesium content            NS             NS           0.001 (a)
Potassium content            NS             NS             NS
Phosphorus content           NS             NS             NS
C/N ratio                  0.002 (a)      0.02 (a)         NS
Humic acids                0.03 (a)         NS             NS
Multiple [R.sup.2]         0.92           0.93           0.84
p-Value of the model      <0.0001        <0.0001        <0.0001

NS--not significant; (a)--negative impact.
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Author:Grantina-Ievina, Lelde; Saulite, Dace; Zeps, Martins; Nikolajeva, Vizma; Rostoks, Nils
Publication:Estonian Journal of Ecology
Article Type:Report
Geographic Code:4EXLA
Date:Dec 1, 2012
Words:11490
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