Effects of intercropping grasses on soil organic carbon and microbial community functional diversity under Chinese hickory (Carya cathayensis Sarg.) stands.
Chinese hickory (Carya cathayensis Sarg.) is a unique, woody nut and oil tree species. It is mainly distributed in Zhejiang and Anhui provinces of eastern China (Chen et al. 2010). The total area of Chinese hickory stands is ~8.93 x [l0.sup.5] ha, and its economic benefits reached 45 000 CNY (~US$7260) [ha.sup.-1] in 2011 (Wang et al. 2011).
In order to improve the yields and quality of Chinese hickory, intensive management, including heavy application of chemical fertiliser and long-term application of herbicides, has been adopted by farmers. Each year, compound fertiliser (N : [P.sub.2][O.sub.5]: [K.sub.2]O, 15:15:15, >750 kg [ha.sup.-1] [year.sup.-1]) is spread in the stands. In addition, large amounts of herbicides such as glyphosate have been applied on the soil surface in the production of the Chinese hickory stands; this eliminates understorey shrubs and weeds, and changes multi-storey into single-storey plantations. The bare soil surface under Chinese hickory stands has led to severe soil erosion (Xia et al. 2007), a decrease in soil organic carbon (SOC) content (Xia et al. 2007; Wang et al. 2011), and the ecological deterioration of the environment, all of which seriously affect the sustainability of Chinese hickory production.
Content of SOC and its dynamic equilibrium might be important factors in determining soil nutrient storage and supply, soil structure stability, soil water-holding capacity and plant growth (Doran and Parkin 1994; Jiang et al. 2009). Soil organic matter is not only an important indicator of soil fertility, but also a key biological indicator of soil health (Larson and Pierce 1991; Doran and Parkin 1994; Clapp and Hayes 1999), because it can be associated with different soil chemical, physical and biological processes. It has been widely considered one of the best indicators of soil quality (Goulding et al. 2000; Jiang et al. 2009).
Soil microorganisms are vital for the continuing cycling of nutrients and for driving aboveground ecosystems (Kennedy and Gewin 1997; Cairney 2000; Klironomos et al. 2000). Soil microbial diversity is considered of immense significance to improve soil quality because soil microbes are involved in many important soil processes (such as soil organic mineralisation), and microbial functional diversity is regarded as more ecologically relevant than taxonomic diversity (Hofinan et al. 2004).
Sod cultivation is a management mode that involves planting herbs between fruit trees or using natural grasses as soil cover crops (Clenn and Wclket 1991; Xia et al. 2007; Qian et al. 2010; Yu et al. 2011). Sod cultivation with no-tillage (Wang et al. 2011) has been used in the soil management of Chinese hickory stands. Previous studies mainly focused on soil degradation, soil erosion, and nutrient loss, but studies into the effects of sod cultivation on functional diversity of soil microorganism are lacking. We hypothesise that intercropping cover crops under Chinese hickory stands may significantly increase SOC stock and labile organic C concentrations, and improve microbial community functional diversity. Therefore, a field experiment was undertaken to determine the effects of intercropping on SOC contents, microbial biomass C (MBC) and nitrogen (MBN), water-soluble organic C (WOC) and N (WON), and microbial community functional diversity, and to correlate the concentrations of SOC with microbial community functional diversity.
Materials and methods
This study was carried out in Tuankou town (119[degrees]08'54.2" E and 30[degrees]03'02>>N), Lin'an city, Zhejiang Province, eastern China. This area has a typical central-subtropical climate with an average annual temperature of 16.4[degrees]C and average annual rainfall of 1628 mm. The average annual sunshine hours and days free of frost in the region are 1774h and 235 days, respectively. The soil, derived from slate, is classified as red soil (Ferralic Cambisol; FAO 2006).
A field experiment was conducted on a pure Chinese hickory stand with a density of 300 plants [ha.sup.-1], which is the standard density in China. The elevation of the study site ranged from 200 to 240 m, with a slope of 20[degrees]. Tree age of the stand was 38 years and canopy density was 70%. The stand had been subject to intensive management for 10 years. The stand was managed by annual application of inorganic fertilisers, deep tillage (to 20-30 cm) and removal of understory vegetation. Compound fertiliser (N : [P.sub.2][O.sub.5]: [K.sub.2]O, 15 : 15 : 15) was applied at the rate of 750 kg [ha.sup.-1] [year.sup.-1] in early May and early September every year. There was no understory vegetation because of long-term tillage and herbicide application before the experiment.
The experimental treatments were: (i) clean tillage, (ii) intercropping rapeseed (Brassica rapa L.), (iii) intercropping ryegrass (Lolium perenne L.), (iv) intercropping Chinese milk vetch (Astragalus sinicus L.). The experiment was arranged in a randomised block design with three replications. The size of the plots was 10 m by 10 m. Buffer strips of 4 m were established around the experimental plots. Management practices were performed according to conventional practices used by farmers.
The experiment began on 5 September 2008 and ended 18 April 2012. At the start of the experiment, the seeds of rapeseed, ryegrass, and Chinese milk vetch (30 kg [ha.sup.-1]) were sown to their respective plots. Each year in May, ~80% of the growth in the intercropped plots was cut and covered on the surface soil under the Chinese hickory stand. Seed from the remaining 20% of intercropped species was germinated and grown in the following year. The biomass cut from the intercropped plots is given in Table 1. For the intercropped plots, no herbicides were applied. For the clean tillage plots, 20% glyphosate at 300 kg [ha.sup.-1] was sprayed on the soil surface on 25 April, 24 June and 27 August.
Soil samples were collected from each treatment at 0-20 cm depth before the experiment commenced (2 September 2008) and after cultivation for 4 years (18 April 2012). Twenty cores (4 cm diameter) per plot were randomly taken and mixed together. Soil samples of each plot were divided into two parts: one part was passed through a 2-mm sieve and kept in the refrigerator at 4[degrees]C for the analysis of SOC and functional diversity of microbial communities within 2 days; the second part was air-dried at room temperature and crushed to pass a through 2-mm sieve and mixed thoroughly for other analyses.
Chemical and biological analyses of soils
Soil properties were determined according to the standard methods in China (Agricultural Chemistry Committee of China 1983). SOC was measured using the wet combustion method with 133 mmol [L.sup.-1] of [K.sub.2] [Cr.sub.2][O.sub.7] at 170-180[degrees]C and total N was measured by the semi-micro-Kjeldahl method. Hydrolysable N was hydrolysed using 0.1 mol [L.sup.-1] of NaOH. Available phosphorus (P) and potassium (K) were determined by the Bray-1 method and the N[H.sub.4]OAc extract-flame photometric method, respectively. The pH (soil: [H.sub.2]O, 1 : 5) was measured using a pH meter. The WOC and WON were measured with the method modified by Jones and Willett (2006). The soil MBC and MBN were determined using the chloroform fumigation--extraction method (Vance et al. 1987). EcoPlates[TM] (Biolog, Hayward, CA, USA) were used to study the substrate utilisation pattern of soil microbial communities. Briefly, fresh soil (10 g) was added to 100 mL of distilled water in a 250-mL flask and was shaken at 200 rpm for 10 min; 10-fold serial dilutions were made and 1000-fold dilution was used to inoculate the EcoPlates. Plates were incubated at 25[degrees]C for 7 days, and colour development was measured as absorbance (A) using a EMax Microplate Reader (Molecular Devices, Sunnyvale, CA, USA) at 590 nm and the data were collected using MicroLog 4.01 software (Biolog) (Abou-Zeid 2012).
For [sup.13]C-nuclear magnetic resonance (NMR) analysis, soil samples were pre-treated with hydrofluoric acid (HF) to remove [Fe.sup.3+] and [Mn.sup.2+] thereby increasing the signal: noise ratio of the instrument. The detailed procedure was described in Li et al. (2010). The HF-treated soil samples were analysed using cross-polarisation magic-angle-spinning (CPMAS) solid-state NMR spectroscopy (Avance II 300 MH; Bruker, Billerica, MA, USA). This measurement included the use of a 7-mm CPMAS detector, frequency of 100.5 MHz, MAS spinning frequency at 5000 Hz, contact time at 2 ms, and recycle delay time at 2.5 s. The external standard used for chemical shift determination was hexamethylbenzene (methyl at 17.33 ppm).
Data were statistically analysed using analysis of variance (ANOVA), and the treatment differences were estimated with Tukey HSD's Multiple Range Test. All statistical analyses were carried out with PASW[R] Statistics for Windows version 18.0 (SPSS Inc., Chicago, IL, USA).
Physical and chemical properties of soils
Soil samples (0-20 cm) collected in April 2012 were used to compare the soil physical and chemical properties in the different treatments (Table 1). Compared with soils samples taken before the experiment, clean tillage reduced soil pH by 0.16 and silt content by 13.7 g [kg.sup.-1], and increased hydrolysable N by 14.0 mg [kg.sup.-1], sand content by 10.0g [kg.sup.-1] and bulk density by 0.05 g [cm.sup.-3]. Available P and K as well as clay content were little affected by clean tillage.
The intercropping treatments increased soil pH by 0.18-0.44 compared with the clean tillage treatment. There were significant differences in soil pH between clean tillage and intercropping rape. Intercropping increased available N, P and K in the soil by 25.1-54.2, 4.2-6.0 and 0 22.5 mg [kg.sup.-1], respectively, compared with the clean tillage treatment. There were significant differences in available N, P, and K between clean tillage and intercropping Chinese milk vetch (P< 0.05). Intercropping decreased sand content by 30.4-14.7 g [kg.sup.-1] and increased silt content by 29.3-48.3 g [kg.sub.-1], respectively, compared with the clean tillage treatment. Clay contents in the treatments were not affected by intercropping grasses.
Soil organic C and N
Intercropping treatments increased (P< 0.05) SOC contents by 23.1% (rape), 26.6% (ryegrass) and 24.7% (Chinese milk vetch) compared with clean tillage; there were no significant differences in SOC contents among the intercropping treatments (Fig. 1). The C:N ratios in 0-20cm soil depth increased from 8.9 in the clean tillage treatment to 10.1-10.2 in the intercropping treatments. Total N contents were not affected by intercropping (P > 0.05).
Soil microbial biomass carbon and nitrogen
The concentrations of MBC and MBN in the soil were significantly enhanced by intercropping (Table 2). After intercropping for 4 years, the concentrations of MBC and MBN in the treatments intercropped with rape, ryegrass and Chinese milk vetch were increased by 138.6, 159.7, 144.2% and 62.0, 60.3, 47.2% (Pc 0.05), respectively.
The concentrations of MBC and MBN in the intercropped treatments were 250.3-272.4 and 13.7-15.1 mg [kg.sup.-1], respectively. There were no significant differences in MBC and MBN concentrations among the three intercropped treatments.
The concentrations of WOC and WON in the treatments intercropped with rape, ryegrass and Chinese milk vetch were increased by 56.2, 69.5, 66.1% and 10.9, 17.5, 20.7%, respectively. The concentrations of WOC and WON in the intercropped plots were 43.7-17.4 and 2.0-2.2 mg [kg.sup.-1] respectively. There were no significant differences in WOC and WON concentrations among the three treatments. Compared with clean tillage, intercropping increased the MBC:SOC and WOC: SOC ratios by 93.7-106.3% and 23.5-35.3% (P<0.05), respectively, and increased the MBC: MBN and WOC: WON ratios by 47.4-66.0% and 37.4 44.0% (P< 0.05), respectively.
Structure of soil organic carbon
The NMR spectrum of soil SOC under the Chinese hickory stand can be divided into seven resonance regions (Fig. 2): alkyl C (0-45 ppm), N-alkyl C (45-60 ppm), O-alkyl C (60-90 ppm), acetal C (90-110 ppm), aromatic C (110-145 ppm), phenolic C (145-165 ppm) and carbonyl C (165-210 ppm).
The percentages of all C component types can be obtained from the regional integration of the NMR spectrum curve (Table 3). Intercropping rape, ryegrass and Chinese milk vetch increased soil carbonyl C by 36.9, 29.9 and 33.9%, respectively (P< 0.05), and decreased alkyl C, O-alkyl C and aromatic C by 10.0-16.4, 18.9-20.9 and 10.5-16.6%, respectively, compared with clean tillage (P< 0.05). There were no significant differences among the intercropping treatments in the increase in soil carbonyl C and the decreases in alkyl C, O-alkyl C, and aromatic C. The of aliphatic C : aromatic C and hydrophobic C : hydrophilic C ratios and aromaticity percentage in soil under Chinese hickory were not affected by intercropping.
Average well-colour development and soil microbial diversity index
The data in Fig. 3 show that the different treatments demonstrated a sigmoid model suggesting that the soil microbial activities increased with time. Soil AWCD of the different treatments increased slowly in the first 24 h, and then rapidly up to 144h, and finally there was little change from 144 to 192 h. At 192 h of incubation, the average values of soil AWCD for the ryegrass, Chinese milk vetch, rape, and clean tillage treatments were 1.244, 1.231, 1.187, and 1.080, respectively. The results of Tukey HSD multiple range showed that the soil AWCD values of the three intercropping treatments were greater than that of the clean tillage treatment (P< 0.05), whereas there were no significant differences in the soil AWCD values among intercropped treatments.
Both the microbial diversity index (Shannon index, H) and evenness index (E) for the different treatments were in the following order: rape > Chinese milk vetch > ryegrass > clean tillage. The H and E in the rape and Chinese milk vetch treatments were much greater than in the clean tillage treatment (P< 0.05), but there were no significant differences in H and E between the ryegrass and clean tillage treatments (Table 4).
Correlation between soil organic carbon or nitrogen and microbial diversity
Correlation analysis (Table 5) showed that WOC, WON, MBC and MBN in soil were significantly positively correlated with SOC (P<0.05 or P<0.01). Correlation coefficients between WOC or MBC and SOC were higher than between WON or MBN and SOC. The results showed significant positive correlations among WOC, WON, MBC, MBN and AWCD in soil (P<0.05 or P<0.01).
Soil fertility quality
Clean tillage resulted in the aggravation of soil acidification, characterised by a decline in soil pH, and soil erosion, characterised by a decline in silt content and an increase in sand content, compared with physical and chemical properties of soil before the experiment (Table 1). An interaction was found between glyphosate and chemical fertilisers. The results of present study concur with those of prior researchers (Xia et al. 2007; Jiang et al. 2009; Wang et al. 2011).
In Phyllostachys praecox (early bamboo) stands with intensive management, long-term application of chemical fertiliser resulted in over-accumulation of soil nutrients, especially soil P (Jing 1999; Jiang et al. 2000). However, accumulation of soil available nutrients was not found in the clean tillage treatment in our study (Table 1).This is because the accumulation of soil available nutrients that occurred from application of chemical fertilisers was counteracted by serious nutrient loss induced by clean tillage.
Sod cultivation improves soil physical properties, and nutrient and organic C contents (Li 2008). Sod cultivation in a fruit orchard reduced soil loss by 19.3-94.9% (Xu 1998) and increased the contents of SOC (Li 2008; Yan et al. 2012) and nutrients (Zhang et al. 2008). In the present study, intercropping reduced soil acidification and increased the contents of hydrolysable N and available P and K. It also reduced soil erosion and improved soil structure compared with the clean tillage treatment (Table 1). It may be that the beneficial effects of intercropping species on soil nutrients and soil erosion were much greater than the negative effects of clean tillage.
Forest management, especially long-term, intensive management, markedly change both the concentration and storage of SOC (Jandl et al. 2007). The reasons for this may be: first, intercropping grass and other species greatly increases plant biomass in the soil and degree of coverage on the soil surface; second, clean tillage accelerates surface soil loss; third, heavy application of inorganic fertilisers could increase the decomposition of soil organic matter, which results in a decrease in SOC pools (Mancinelli et al. 2010). These observations are similar to earlier findings with apples (Meng and Zhang 2003), grapevines (Pan et al. 2004) and bayberry (Myrica rubra) (Yan et al. 2012). Sod cultivation increased SOC contents by 54.4% in a grapevine orchard (Pan et al. 2004), 30% in an apple orchard (Meng and Zhang 2003) and 25.2-48.9% in a bayberry orchard (Yan et al.2012).
The increases in the concentrations of MBC, MBN, WOC and WON as well as in the ratios MBC : MBN, WOC : WON, MBC: SOC and WOC : SOC in the treatments of intercropping grasses (Table 2) were attributed to increases in SOC concentrations. This is because the concentrations of MBC, MBN, WOC and WON appeared highly correlated with the concentrations of SOC. However, the rates of increase in the concentrations of MBC, MBN, WOC and WON were greater than in the concentrations of SOC, which resulted in increases in the ratios MBC : MBN, WOC : WON, MBC : SOC and WOC: SOC.
Structure of soil organic carbon
Solid-state [sup.13]C-CPMAS NMR has been used extensively to reveal the changes in chemical composition of SOC induced by different management practices (Ussiri and Johnson 2003; Huang et al.2008; Li et al. 2010). Fertilisation and tillage have a marked impact on the chemical composition of SOC (Tatzber et al. 2008; Huang et al. 2011). Huang et al. (2011) reported that long-term fertilisation increased the alkyl C content and the A : O-A alkyl C ratio in the light fraction of soil organic matter at the 0-5 cm soil depth in a second-rotation Pinus radiata D. Don plantation. Tatzber et al. (2008) found that conventional tillage significantly decreased O-alkyl C content in a cropland soil.
In the present study, there were seven significant resonance areas in the NMR spectra in the soil under the Chinese hickory stand (Fig. 2). The ratio alkyl C ([C.sub.0-45 ppm]): alkoxy C ([C.sub.45-110ppm]) reflects the alkylation degree of humic substances, which can be used as an index of organic C decomposition (Ussiri and Johnson 2003). The ratio hydrophobic C: hydrophilic C [([C.sub.0-45 ppm] + [C11.sub.0-165 ppm]): ([C.sub.45-110 ppm]) + [C.sub.165-210 ppm])] reflects the degree of hydrophobicity of humic substances. The greater the ratio, the higher the stability of SOC (Spaccini et al. 2006). The ratio aliphatic C ([C.sub.0-110 ppm]): aromatic C ([C.sub.110-165ppm]) reflects the complexity of molecular structure in humic substances. The greater the ratio, the more aliphatic side chains, the lower the degree of condensation, and the simpler the molecular structure in humic substances. Aromaticity (%) ([C.sub.110-165ppm]:[C.sub.0-165ppm] x 100) reflects the complexity of the molecular structure in organic C; the larger the value, the more aromatic the nucleus structure, and the more complex the molecular structure (Hoffman et al. 2004; Xu et al. 2009).
The results of the present study show that intercropping not only increased the content of SOC, but also changed the structure of SOC. Intercropping significantly increased the percentage of soil carboxyl C that is easily oxidised (Table 3), which is consistent with increased MBC and WOC concentrations, because a large amount of organic materials was returned to the soil after the plants died. By contrast, the intercropping treatments significantly decreased the percentages of alkyl C, O-alkyl C and aromatic C compared with clean tillage (Table 3).
Slight decreases in the alkyl C : alkoxy C and hydrophobic C: hydrophilic C ratios in the intercropping treatments (Table 3) indicate a slight decrease in the stability of SOC. The reason for this may be that decomposition of newly formed SOC was much easier in the intercropped treatments than in the treatment with clean tillage. However, intercropping resulted in a slight increase in the complexity of molecular structures in organic carbon (Table 3).
Microbial community functional diversity
Soil microbial diversity is important for the maintenance of soil processes (Oilier et al. 1997). Moreover, microbial catabolic diversity in soils is highly linked with organic C pools (Degens et al. 2000). Soil microbial community functional diversity is modified by factors including fertilisation (Kanchikerimath and Singh 2001; Bunemann et al. 2004; Xu et al. 2007), tillage (Oilier 1996; Lupwayi et al. 1998), crop rotation (Lupwayi et al. 1998; Bunemann et al. 2004; Bossio et al. 2005), organic matter amendments (Stark et al. 2008) and land use history (Yao et al. 2006).
Some studies revealed that the soils under conventional tillage had lower AWCD and H values than those under reduced tillage (Giller 1996; Lupwayi et al. 1998) because of a reduction in substrate richness and microbial uniformity under conventional tillage. Introduction of leguminous crops for a season into a conventional system of continuous cultivation of maize (Zea mays L.) also increased microbial diversity (Bunemann et al. 2004; Bossio et al. 2005).
The AWCD value each well in the EcoPlate is an important index that reflects the soil microbial community functional diversity (Yang and Hua 2000). In our study, AWCD values of the intercropped treatments were significantly greater (P<0.05) than of clean tillage over the whole incubation period (196 h), which indicates greater individual numbers and abundance of microorganism populations in the intercropped treatments (Fig. 3). Intercropping significantly (P< 0.05) increased soil microbial community function diversity, as revealed by higher the values of H and E indices (Table 4). The improvement in soil microbial community functional diversity induced by intercropping was mainly attributed to marked increase in SOC (Mancinelli et al. 2010; Bossio et al. 2005) and changes in soil environment (water, temperature, aeration, etc.).
Correlation between soil organic carbon or nitrogen and microbial diversity
Relationships between labile organic C and SOC have been extensively studied. The present results showed that WOC, WON, MBC, and MBN in the soil are positively and significantly correlated with soil SOC (Table 5), consistent with previous studies (Beyer 1995; Webster et al. 2001; Chen et al. 2004; Huang et al. 2008; Li et al. 2010). SOC and WON were significantly, positively correlated with soil microbial community diversity indices (Table 5), because labile organic C and N are easily utilised by soil microorganisms (Chen et al. 2004; Uchida et al. 2012). The results of this study concur with prior research of An et al. (2011), who reported significant positive correlations between AWCD and H in soils under nine plant species (P<0.01).
Soil biochemical parameters (SOC, MBC, MBN, WOC and WON) were strongly (P<0.05 or P<0.01) correlated with microbial community diversity parameters (AWCD) (Table 5), which suggested that these parameters might provide consistent indications of soil quality.
Under the conditions of this study, changes in soil fertility and soil microbial community diversity were largely determined by tillage, fertilisation, and intercropping. Compared with clean tillage, sod cultivation of intercropped rape, ryegrass, and Chinese milk vetch resulted in decreased soil acidification and soil erosion as well as improvement in soil fertility and soil microbial community diversity. Intercropping significantly (P<0.05) increased soil microbial community diversity, as shown by increasing values of AWCD, H and E. The results of this study demonstrate that sod cultivation is an effective soil management practice that improves soil fertility quality and soil microbial community diversity and may improve the sustainability of Chinese hickory production. The results from this work will provide essential information for reasonable utilisation of sod cultivation in Chinese hickory production.
The authors acknowledge funding support from Zhejiang Provincial Priority First-level Discipline of Forestry Open Funded Projects (KF201317), the National Natural Science Foundation (No. 41201323), the Zhejiang Province Natural Science Foundation (No. LY13C160010) and Key Science and Technology Development project of Zhejiang Province (2011C12019).
Received 24 January 2014, accepted 15 May 2014, published online 19 August 2014
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* Jiasen Wu and Haiping Lin contributed equally to this work.
Jiasen Wu (A,B),*, Haiping Lin (A,C),*, Cifu Meng (B), Penkun Jiang (B), and Weijun Fu (B,C)
(A) The Nurturing Station for the State Key Laboratory of Subtropical Silviculture, Zhejiang A & F University, Lin'an 311300, China.
(B) Zhejiang Provincial Key Laboratory of Carbon Cycling in Forest Ecosystems and Carbon Sequestration, Zhejiang A & F University, Lin'an 311300, China.
(C) Corresponding authors. Emails: email@example.com; firstname.lastname@example.org
Table 1. Basic properties of soils (0-20 cm) and the biomass of the intercropped species returned to the soil under Chinese hickory stand after 4 years of the experiment Within columns, means followed by the same letter are not significantly different at P=0.05 (Tukey HSD multiple range test) Treatment PH Hydrolysable N Before treatment 5.92 145 Clean tillage 5.77 [+ or -] 0.2 b 159.2 [+ or -] 8.1 b Rape 6.21 [+ or -] 0.2 a 184.3 [+ or -] 7.2 ab Ryegrass 5.80 [+ or -] 0.3 ab 189.5 [+ or -] 9.1 ab Chinese milk vetch 5.95 [+ or -] 0.3 ab 213.4 [+ or -] 15.1 a Treatment Available P Available K (mg [kg.sup.-1]) Before treatment 7.9 36.5 Clean tillage 8.8 [+ or -] 0.9 b 36.7 [+ or -] 3.8 b Rape 13.0 [+ or -] 1.2 ab 36.7 [+ or -] 3.7 b Ryegrass 13.7 [+ or -] 1.4 ab 37.5 [+ or -] 3.9 b Chinese milk vetch 14.8 [+ or -] 1.5 a 59.2 [+ or -] 5.7 a Treatment Sand Silt (g [kg.sup.-1]) Before treatment 295.5 501.4 Clean tillage 305.5 [+ or -] 15.2 a 487.7 [+ or -] 18.1 b Rape 262.3 [+ or -] 14.8 b 525.0 [+ or -] 22.4 a Ryegrass 260.8 [+ or -] 13.9 b 536.0 [+ or -] 24.6 a Chinese milk vetch 275.1 [+ or -] 14.1 ab 517.0 [+ or -] 21.7 ab Treatment Clay Bulk density (g [cm.sup.-3]) Before treatment 203.2 1.20 Clean tillage 206.8 [+ or -] 6.9 ab 1.25 [+ or -] 0.2 b Rape 213.1 [+ or -] 5.5 a 1.15 [+ or -] 0.1 ab Ryegrass 202.9 [+ or -] 4.2 b 1.18 [+ or -] 0.1 a Chinese milk vetch 207.9 [+ or -] 4.3 ab 1.16 [+ or -] 0.1 ab Treatment Biomass (dry wt, kg [ha.sup.-1]) Before treatment Clean tillage Rape 11100 [+ or -] 1135 Ryegrass 13900 [+ or -] 1410 Chinese milk vetch 12550 [+ or -] 1280 Table 2. Comparison of the concentrations of microbial biomass carbon and nitrogen (MBC, MBN) as well as water-soluble organic C and N (WOC, WON) in the soils (0-20 cm) under Chinese hickory stand for different treatments after 4 years of the experiment Within columns, means followed by the same letter are not significantly different at P=0.05 (Tukey HSD multiple range test) Treatment MBC MBN (mg [kg.sup.-1]) Before treatment 152.7 11.2 Clean tillage 104.9 [+ or -] 12.6 b 9.3 [+ or -] 0.9 b Rape 250.3 [+ or -] 32.3 a 15.1 [+ or -] 1.4 a Ryegrass 272.4 [+ or -] 38.4 a 14.9 [+ or -] 1.3 a Chinese milk vetch 256.2 [+ or -] 34.6 a 13.7 [+ or -] 1.4 a Treatment WOC WON (mg [kg.sup.-1]) Before treatment 32.1 1.83 Clean tillage 28.0 [+ or -] 3.2 b 1.78 [+ or -] 0.1 b Rape 43.7 [+ or -] 5.7 a 1.97 [+ or -] 0.2 ab Ryegrass 47.4 [+ or -] 6.0 a 2.09 [+ or -] 0.2 ab Chinese milk vetch 46.4 [+ or -] 6.6 a 2.15 [+ or -] 0.2 a Treatment MBC/MBN WOC/WON MBC/SOC WOC/SOC (%) (%) Before treatment 13.6 17.5 0.89 0.19 Clean tillage 11.3 b 15.7 b 0.63 b 0.17 b Rape 16.6 a 22.0 a 1.22 a 0.21 a Ryegrass 18.3 a 22.7 a 1.30 a 0.23 a Chinese milk vetch 18.7 a 21.6 a 1.24 a 0.22 a Table 3. Distributions of different chemical shift ranges in total signal intensity for [sup.13]C-NMR in the soils (0-20 cm) under Chinese hickory stand Alkyl C/alkoxy C = ([C.sub.0-45ppm])/([C.sub.45-110ppm]); HBC/HLC, hydrophobicC/hydrophilic C; APC/AMC, aliphatic C/aromatic C = [([C.sub.0/45ppm] + [C11.sub.0-165ppm])/([C.sub.45-110ppm] + [C.sub.165/210ppm])]; APC/AMC, aliphatic C/aromatic C = ([C.sub.0-110ppm])/([C.sub.110-165ppm]); AC, aromaticity = ([C.sub.110-165ppm]/[C.sub.0-165ppm]) x 100. Within columns, means followed by the same letter are not significantly different at P=0.05 (Tukey HSD multiple range test) Treatment Alkyl C N-alkyl C 0-45 ppm 45-60 ppm Clean tillage 9.0 [+ or -] 0.4 a 5.5 [+ or -] 0.4 a Rape 7.6 [+ or -] 0.6 b 5.9 [+ or -] 0.6 a Ryegrass 7.5 [+ or -] 0.5 b 5.8 [+ or -] 0.7 a Chinese milk vetch 8.2 [+ or -] 0.3 b 5.7 [+ or -] 0.7 a Treatment O-alkyl C Acetal C 60-90 ppm 90-110 ppm Clean tillage 15.6 [+ or -] 1.6 a 11.6 [+ or -] 1.2 a Rape 12.4 [+ or -] 1.2 b 12.3 [+ or -] 1.3 a Ryegrass 12.6 [+ or -] 1.1 b 12.4 [+ or -] 1.3 a Chinese milk vetch 12.7 [+ or -] 1.1 b 12.1 [+ or -] 1.4 a Treatment Aromatic C Phenolic C 110-145 ppm 145-165 ppm Clean tillage 28.4 [+ or -] 1.4 a 12.9 [+ or -] 1.4 ab Rape 23.7 [+ or -] 1.3 b 15.1 [+ or -] 1.3 a Ryegrass 25.4 [+ or -] 1.2 b 14.2 [+ or -] 1.3 a Chinese milk vetch 25.3 [+ or -] 1.2 b 13.5 [+ or -] 1.4 ab Treatment Carbonyl C AlkylC/ 165-210 ppm alkoxy C Clean tillage 16.9 [+ or -] 1.8 b 0.28 a Rape 23.2 [+ or -] 2.4 a 0.25 a Ryegrass 22.0 [+ or -] 2.1 a 0.24 a Chinese milk vetch 22.7 [+ or -] 2.1 a 0.26 a Treatment HBC/ APC/ AC HLC AMC (%) Clean tillage 1.01 a 1.01 a 49.7 a Rape 0.86 a 0.98 a 50.4 a Ryegrass 0.89 a 0.97 a 50.8 a Chinese milk vetch 0.88 a 1.00 a 50.1 a Table 4. Indices of microbial function diversity in the soils (0-20 cm) under Chinese hickory stand with intercropping the different grasses (96 h) Within columns, means followed by the same letter are not significantly different at P=0.05 (Tukey HSD multiple range test) Treatment Shannon index (H) Evenness index (E) Clean tillage 3.335 [+ or -] 0.081 b 0.933 [+ or -] 0.014 b Rape 3.616 [+ or -] 0.064 a 0.969 [+ or -] 0.001 a Ryegrass 3.458 [+ or -] 0.178 ab 0.936 [+ or -] 0.035 ab Chinese milk vetch 3.604 [+ or -] 0.071 a 0.972 [+ or -] 0.013 a Table 5. Correlation coefficients (r) between chemical properties and microbial functional diversity in the soils (0-20 cm) under Chinese hickory stand SOC, Soil organic carbon; MBC, microbial biomass carbon; MBN, microbial biomass nitrogen; WOC, water-soluble organic carbon; WON, water-soluble organic nitrogen; AWCD, average well colour development. * P<0.05; ** P<0.01 MBC MBN WOC WON AWCD SOC 0.679 ** 0.348 * 0.645 ** 0.415 * 0.532 ** MBC 0.875 ** 0.736 ** 0.695 ** 0.498 * MBN 0.752 ** 0.498 * 0.453 * WOC 0.548 ** 0.367 * WON 0.435 *
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|Author:||Wu, Jiasen; Lin, Haiping; Meng, Cifu; Jiang, Penkun; Fu, Weijun|
|Date:||Sep 1, 2014|
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