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Variation in soil microbial biomass in the dry tropics: impact of land-use change.

Introduction

Land-use change has impact not only on climate change but also on the dynamics of soil organic matter, biodiversity, and change in ecosystem services in general and, specifically, tropical soils since they are nutrient-limited and highly weathered (Tilman et al. 2001). The degradation rate of natural tropical forest, which covers 7% of the earth's surface, is ~15.4 million ha [year.sup.-1] (Parrotta et al. 1997). Excessive harvesting for timber and/or non-timber forest products, cattle grazing and other changes in land-use patterns arc the major determinants of land degradation, which, in turn, alters the soil quality and vegetation patterns and severely delays or even totally inhibits restoration of the natural forest (ITTO 2002). Degradation of natural forests leads to degradation of forest ecosystems, which become entirely different from the natural forests in terms of soil quality and vegetation cover (Islam et al. 2001). The cultivation of natural forests for raising crops is very common in the dry tropics, owing to population pressure. Agroecosystems are being manipulated by inputs to maximise crop yields, and this is considered one of the major causes of land-use change (Odum 1984; Coleman and Hendrix 1988).

Concerns have been raised for the restoration and reclamation of degraded forests, and this is a great challenge. A restoration strategy is considered successful if it fulfils not only environmental but also social and economic sustainability criteria. Among the several strategies, biofuel plantation is considered an ideal measure for restoration of degraded lands (Ogunwole et al. 2008; Wani et al. 2012). Jatropha curcas, a member of Euphorbiaceae family and a multipurpose perennial shrub, has potential for biofuel production. Although many studies have been concerned with economic aspects of biofuel production, little information is available on its role in the restoration of degraded lands, especially in the dry tropics.

Soil microbial biomass has been identified as vital tool for predicting changes in soil quality related especially to the land-use change, sustainability and the restoration of ecosystems (Kennedy and Papendick 1995). However, the extent and complexity of land-use-induced variations is highly variable and strongly dependent on the particular ecosystem. Although the impact of land-use change on soil microbial biomass dynamics has been widely studied, limited knowledge exists for the dry tropics, especially with reference to restoration of degraded forests. Seasonal variability of soil microbial biomass is, in most cases, explained by soil moisture content (Devi and Yadava 2006) or by soil temperature (Iqbal et al. 2010) in different ecosystems. However, climatic factors controlling soil microbial biomass have been little studied in dry tropics. Moreover, most studies have been limited to the upper soil layer (Sahani and Behera 2001; Patel et al. 2010), whereas for the proper restoration of degraded forests, knowledge of the dynamics of microbial biomass in deeper soil layers seems imperative.

The present study tested the following hypotheses: (i) land use change alters the concentration of soil microbial biomass carbon (C) and nitrogen (N) at different soil depths; (ii) seasonal variations in the concentration of soil microbial biomass C and N are regulated by climatic factors and land-use types; (iii) shifting of microbial community structure in terms of microbial biomass C/N ratio occurs with the land-use change and soil depth; and (iv) restoration of degraded lands can be achieved through plantation of Jatropha curcas. The present study was aimed at estimating the impact of various land-use patterns, i.e. natural forest, degraded forest, agroecosystem and Jatropha plantation, in a dry tropical environment on seasonal variations in the levels of soil microbial biomass C and N, their vertical distribution with soil depth, and changes in the microbial biomass C/N ratio.

Materials and methods

Site description

Of the four sites studied, three (degraded forest, agroecosystem and Jatropha plantation) were at Rajcev Gandhi South Campus, Banaras Hindu University, Barakachha. The fourth site, natural forest, was at the Marihan range, ~7-8 km from Barakachha, at Mirzapur, Uttar Pradesh, India. The study was conducted from September 2010 to June 2012. The sites are at 25.15'N, 82.58'E, and ~81 m above mean sea level. The climate is dry tropical monsoonal with marked seasonality. The year can be divided into three distinct seasons, rainy (July -September), winter (November-February) and summer (April-June), with October and March transitional months. The annual average rainfall is ~1876 mm (range 1700-2052 mm), 95% of which falls during the rainy season. Mean monthly minimum and maximum temperature ranged from 14.2 to 32.5[degrees]C and from 25.5 to 42.8[degrees]C, respectively. Soil of the all land-use types was residual Ultisol, sandy to sandy-loam in texture, and reddish to reddish-brown in colour (Agarwal and Mehrotra 1952).

The forest site was the mixed dry deciduous type dominated by Acacia catechu Wild., Albizia odoratissima Benth., Acacia nilotica (L.) Willd. Boswellia serrata Roxb., Nyctanthes arhortristis L., with scattered trees of Azadirachta indica Juss. and Zizyphus glaberrima Santap. The forest floor was covered with herbaceous vegetation comprising Ocimum americanum L., Pisum arvense L., Rhynchosia minima (L.) DC., Cassia sophera (L.) Roxb., Acrocephalus indicus (Burm. f.) Kuntze., Cynodon dactylon L., and Oplismenus burmannii Ritz. The degraded forest site was dominated by Z. glaberrima, Chrysopogon fulvus Spreng., Heteropogon contortus L., Adina cordifolia Roxb. and scattered trees of Butea monosperma Lamk. Herbaceous vegetation in the degraded forest was dominated by Cassia tora L., Oldenlandia diffusa Roxb., Sporobolus spp., Panicum psilopodium Trin. and Alysicarpus varginalis (L.) DC. The cultivation of degraded forest started in 1979 and it continues at the Rajeev Gandhi South Campus, Barakachha. The crop sequence studied was Oryza sativa (var. HUR 3022)--barley (Hordeum vulgare var. Manjula)-summer fallow. Since June 1990, chemical fertiliser in form of urea, single super phosphate and muriate of potash at the rate of 100, 60 and 40 kg [ha.sup.-1] N, P and K, respectively, have been used annually. With the objective of restoration of degraded forest, Jatropha plantation was started ~10 years ago in a 100-ha area at Rajeev Gandhi South Campus. Jatropha curcas was planted in rows, with an inter-row distance of 2 m and interplant distance 2 m. Evolvulus nummularius L., Glinus oppositifolius (L.) DC., Tephrosia purpurea L., and Cassia tora were the major herbaceous species common to Jatropha plantation.

Soil sampling and analysis

The areas of the various sites, i.e. natural forest, degraded forest, agroecosystem and Jatropha plantation, were ~10, 4.5, 0.0625 and 1 [km.sup.2], respectively. Each site was first divided into three contiguous study sites with areas of 1.61 km x 1.4 km, 1.2 km x 815 m, 220 m x 75 m and 800 m x 200 m, respectively, for natural forest, degraded forest, agroecosystem and Jatropha plantation respectively. A buffer zone in form of a strip was left around all sites as well as between the study sites, of the width 200, 150, 10 and 100 m in natural forest, degraded forest, agroecosystem and Jatropha plantation, respectively. Each study site was further divided into nine sub-sites of 100 m x 100 m for natural forest, degraded forest, and Jatropha plantation, and eight sub-sites of 52 m x 35 m for the agroecosystem, of which five were selected randomly for sampling at a time. From each sub-site, two soil samples were collected (i.e. 10 soil samples in total from each study site) and mixed to represent the single composite sample of a study site.

Soil samples were collected during the rainy, winter and summer seasons in two annual cycles from upper (0-10 cm), middle (10-20 cm) and lower (20-30 cm) layers using soil corer of diameter 4 cm and height 10 cm from each land-use-type site. Soil samples were hand-sorted to remove the visible plant debris and sieved through a mesh screen (2 mm). The chloroform fumigation-extraction method using purified CH[Cl.sub.3] treatment was adopted for the estimation of microbial biomass C and N (Brookes et al. 1985; Vance et al. 1987). Microbial biomass C was determined by the dichromate digestion method, and calculated using the equation: MBC = 2.64[E.sub.C], where [E.sub.C] is the difference between organic C extracted in the [K.sub.2]S[O.sub.4] extracts of fumigated and non-fumigated soils. Microbial biomass N was estimated by N analyser (Gcrhardt unit; C. Gcrhardt GmbH & Co., Bonn, Germany) and calculated using the equation: MBN = [E.sub.N]/0.54, where [E.sub.N] is the difference between the amount of N extracted from the [K.sub.2]S[O.sub.4] extract of fumigated and non-fumigated soil, and 0.54 is the fraction of biomass N extracted after chloroform fumigation.

Soil temperature at all sites was measured for all the three soil layers during the rainy, winter and summer seasons using a portable digital thermometer bearing an external sensor. The temperature probe was placed at the midpoint of the particular soil layer. Soil moisture content was measured for each soil layer during each season and from each land use type. For measuring soil moisture content, 10 g of fresh soil was dried at 105[degrees]C to constant weight. Soil moisture content was calculated as:

Soil moisture content (%) =

{(weight of fresh soil - weight of dry soil)/ weight of dry soil} x 100

Microbial biomass C/N ratio was obtained by dividing the annual mean concentration of the first and second annual cycle of soil microbial biomass C with that of microbial biomass N at different sites and at different soil depths.

Statistical analyses

Data were analysed using SPSS package (version 16; SPSS Inc., Chicago, IL, USA). All the values are expressed as mean [+ or -] standard error. Means were compared using the least square difference (l.s.d.). The impact of ecosystem, season and depth was tested using univariate analysis of variance with mixed effect model. Significance of difference is indicated as P<0.05, P<0.01 and P< 0.001.

Results

Soil microbial biomass C

The level of soil microbial biomass C differed significantly among the land-use types for all seasons and depths, ranging from 93.65 to 723.68 [micro]g [g.sup.-1] dry soil. The level of soil microbial biomass C was least during rainy season, and increased through winter to the maximum in summer for all the land-use types and at all the depths (Fig. 1). Among the land-use types, the level of soil microbial biomass C was highest (724 [micro]g [g.sup.-1]) in the natural forest in the upper layer, followed in decreasing order by Jatropha plantation, degraded forest, and the minimum (257 [micro]g [g.sup.-1]) in the agroecosystem during all three seasons. The same trend applied in the middle and lower layers (Fig. 1). To assess the response of soil microbial biomass C of the three soil depths under different land-use types, the microbial biomass C values were averaged for the first and the second annual cycle. The mean annual level of microbial biomass C was highest in the upper layer and decreased consistently with increasing depth for all land-use types, rang between 95.27 and 709.55 [micro]g [g.sup.-1] soil (Table 1).

Univariate analysis of variance of the data for the two annual cycles indicated that depth had a slightly more pronounced effect on microbial biomass C than season and land-use type (Table 2). The land use type x season interaction had more effect on the microbial biomass C than land use type x depth and land use type x season x depth interactions. The effect of the season x depth interaction on microbial biomass C was not significant.

Soil microbial biomass N

The trend for microbial biomass N was similar to that for microbial biomass C under all land-use types, seasons and soil depths, and ranged from 3.46 to 81.93 [micro]g [g.sup.-1] (Fig. 2). Microbial biomass N was highest in natural forest during summer at all soil depths, followed in decreasing order by Jatropha plantation, degraded forest, and least in the agroecosystem. The same trend was observed during rainy and winter seasons. Average values of microbial biomass N of two annual cycles were highest at the upper layer and the lowest at the lower layer, and varied between 3.46 and 81.93 [micro]g [g.sup.-1] soil (Table 1).

Microbial biomass N was influenced more by season than soil depth and land use type according to univariate analysis of variance (Table 2). The effect of land-use type x depth interaction on soil microbial biomass N was more pronounced than that of season x depth, land use type x season and the interaction of all factors, such as land use types, season and depth.

Variation in microbial biomass C/N ratio

Across all the land-use types, the mean microbial biomass C/N ratio varied from 7.81 to 25.97, and increased with depth to reach a maximum in the lower layer for all land-use types (Table 3).

Seasonal variations in soil temperature and moisture content

Distinct seasonal variation was observed in soil temperature for all land-use types, with the minimum during winter and maximum during summer (range 19-34[degrees]C; Fig. 3). Soil moisture content varied distinctly with season, being maximum during the rainy season and minimum during summer for all land-use types, and ranging between 2 and 54% (Fig. 3). Through the two annual cycles, soil microbial biomass C and N in the soil profile of 0-30 cm showed significant, strong negative correlations with soil moisture content, and weak positive correlations with soil temperature for each land-use type (Table 4).

For the two annual cycles across the three seasons and three soil depths, the correlation coefficient for the relationship between soil moisture and soil microbial biomass C was r = -0.55 to 0.80 (d.f. = 18, P<0.05) and for soil moisture and soil microbial biomass N was r = 0.40-0.62 (d.f. = 18, P<0.05) for different land use types. The weakly positively correlations of soil temperature with soil microbial biomass C (r = 0.31-0.37, d.f. = 18, P > 0.05) and soil microbial biomass N (r = 0.29-0.38, d.f.= 18, P > 0.05) were not statistically significant (Table 4).

Discussion

Impact of land use change on soil microbial biomass C and N

Changes in land-use pattern from natural forest to degraded forest resulted in 28% and 30% decrease in the annual mean level of soil microbial biomass C and N, respectively (Figs 1 and 2), which might be attributed to reductions in the vegetation cover leading to lower levels of litter input, root necromass and root exudates to the soil. Soil microbial biomass is reportedly influenced by plant litter production through changes in the labile organic C, soil nutrients and microclimatic regimes (Zak et al. 1994; Garcia-Oliva el al. 2003). Greater amounts of litter under native forest than under other land-use types supported greater microbial biomass as reported by Nsabimana et al. (2004), Patel et al. (2010), and Nunes et al. (2012) in different regions. High levels of root debris and exudates supported high microbial activity (Hutsch et al. 2002). In addition, degradation of natural forest leads to opening of the canopy cover and increases the interference of physical factors such as light intensity, wind velocity and soil moisture content. As the canopy opens, incident light intensity and wind velocity increase, decreasing the moisture content, which, in turn, stimulates organic matter mineralisation leading to reductions in microbial biomass.

A 40% and 47% reduction in soil microbial biomass C and N, respectively, was observed in the agroecosystem due to cultivation of natural forest soil for >30 years in the present study. In agroecosystems, the bulk of aboveground biomass is harvested out of the system, leaving behind crop stubbles and roots and leading to very low organic matter input to the soil. In addition, tillage practices expose the native soil organic matter to oxidations and mineralisation (Elliott 1986; Golchin et al. 1995), leading to further reductions in the microbial biomass. These factors collectively may explain the trend toward considerable decrease in the levels of soil microbial biomass in the agroecosystem. Srivastava and Singh (1989) reported 58% and 45% reduction in microbial biomass C and N, respectively, following 40 years of cultivation of the mixed forest. Dalai and Mayer (1987) also reported a considerable decrease in soil microbial biomass following cultivation of natural ecosystems.

Compared with the natural forest, the levels of soil microbial biomass C and N were 18% and 15% lower, respectively, in Jatropha plantation and 28% and 30% lower in the degraded forest. In other words, Jatropha plantation lasting 10 years on the degraded forest increased the microbial biomass C and N by 15% and 21%, respectively, over the degraded forest. Such a rise in soil microbial biomass C and N indicated the trend of restoration of degraded forest towards the natural forest occurring with Jatropha plantation. Jatropha plants generally shed all their nutrient-rich leaves during late winter (M. K. Singh, unpublished data). These leaves, along with the profusely branched root system limited to upper 20 cm, could have added large amounts of organic matter to the soil, in turn stimulating the microbial biomass.

Variation in soil microbial biomass with soil depth

In the present study, the higher level of microbial biomass near the soil surface was probably due to the greater proportion of roots and the accumulation of plant litter compared with middle or lower layer of the soil horizon in all the land-use types (Table 1). With increasing soil depth soil, moisture availability and soil aeration decreased, whereas the bulk density increased (M. K. Singh, unpublished data), and this may be another factor in the decrease in microbial biomass through the soil profile (Ralte et al. 2005). Such trends of decline in the soil microbial biomass with increasing soil depth are also reported from forests in the subtropics (Singh et al. 2007), and in grasslands and agroecosystems (Singh and Yadava 2006), but not from the dry tropics.

Microbial biomass C/N ratio

Microbial biomass C/N ratio increased with increasing soil depth across all the land-use types (Table 3), despite the fact that the level of microbial biomass C and N decreased with increasing soil depth (Table 1). The differential decrease in microbial biomass C and N with soil depth might explain the current trend of microbial biomass C/N ratio. An increase in microbial biomass C/N ratio is considered an indication of changes in the microbial community, with the possible dominance of fungi over bacteria; thus, it could be suggested that the lower layer is fungi-dominated compared with upper layer for all of the sites (Barbhuiya et al. 2004; Patel et al. 2010). Since the rate of N mineralisation is regulated by the microbial biomass C/N ratio and C input (Tahovska et al. 2013), the increase in microbial C/N ratio with soil depth may also support higher rates of immobilisation relative to the upper layer. Microbial C/N ratio has been suggested as the indicator of ecosystem recovery, since the lower the ratio, the shorter will be the time required for build-up of the microbial population and its activity (Arunachalam and Pandey 2003). Among the land-use types investigated, the microbial biomass C/N ratio was lowest in the Jatropha plantation at all the depths and maximum in the agroecosystem, indicating that the rate of restoration could be faster in Jatropha plantation than the agroecosystem. It is possible that the restoration of lower layers would take much longer than restoration of the upper layer as apparent from the lower C/N ratio in the upper than lower layer (Table 3). Since the time of recovery of any ecosystem depends on the component that takes longest to recover, it is important to consider the lower depths of soil horizons rather than just the surface layer when designing recovery strategies for any ecosystem.

Seasonal variation in soil microbial biomass

Although the land-use types were quite different and this had impact on the amount of soil microbial biomass, the seasonal variations were common to all four sites, indicating that climatic factors played important roles in regulating seasonal variations in the soil microbial biomass (Figs 1 and 2). Contrary to our findings, it has also been reported that the level of soil microbial biomass was more strongly affected by land-use changes than the climatic factors (Guo-chao and Zhen-li 2003; Kara and Bolat 2008; Tripathi and Singh 2009; Pabst et al. 2013). The significant negative correlation coefficient between the level of microbial biomass C or N and moisture content among all land-use types, and the weak positive relationship between microbial biomass C or N and soil temperature (Table 4) indicated that soil moisture content rather than soil temperature could be a better indicator of seasonal variations in soil microbial biomass C and N. By contrast, Devi and Yadava (2006) reported significant positive correlation between soil moisture and soil microbial biomass in wet tropical, deciduous forest of India. In these dry tropics, the availability of soil moisture depends on rainfall. Because variability in rainfall pattern has also been projected by climate change modelling studies for our region (Menon et al. 2013), any change in the rainfall pattern may have an impact on the soil microbial biomass dynamics, which, in turn, would influence the C and N cycling in the region.

A marked seasonal variation in the level of soil microbial biomass was observed in this study for all sites and depths, with the lowest during the rainy season and highest during summer. This could be explained based on availability of soil moisture content. During the rainy season, ample availability of soil moisture in all the land-use types may have provided favourable conditions for growth of both the plants and the microbes, leading to strong competition for nutrients. Lower microbial biomass under nutrient-limited conditions was reported to be due to less stable, more dynamic microbial biomass with higher turnover rate (Wardle et al. 1999; Singh et al. 2009). During summer, the availability of soil moisture was minimum at all sites, leading to elimination of all of the herbaceous vegetation in the natural forest, degraded forest and Jatropha plantation, whereas in the agroecosystem, crops were harvested leaving only the stubbles, which also dried up subsequently. This collectively led to the minimum competition between microbes and plants in all of the land-use types, and could be the reason for high accumulation of the less dynamic and more dormant microbial biomass. By contrast, Devi and Yadava (2006) reported high soil microbial biomass during the rainy season for a subtropical, mixed oak forest, and Singh and Yadava (2006) observed high soil microbial biomass during summer in grassland and agroecosystem but not in the forest. The concentration and turnover of microbial biomass has been reported to have profound impact on C and N cycling in such ecosystems. Overall, such studies will a greatly assist in designing restoration strategies.

Conclusion

The impact of land-use change on soil microbial biomass C and N was different at the various depths of the soil profile. The most severe impact of conversion of the natural forest was observed in the agroecosystem, as the level of soil microbial biomass was lowest. By contrast, Jatropha plantation, having higher microbial biomass through the soil profile, favoured the restoration of degraded forest towards natural forest. Variations in microbial biomass C/N ratio among the land-use types indicated that it could be used as an index of ecosystem restoration. It is suggested that designing effective restoration strategies for degraded forests, especially in the dry tropics, should be based on holistic, site-specific studies that include not only the upper soil layer but the entire soil profile. Based on high soil microbial biomass and faster recovery rates, it is suggested that Jatropha plantation could be adopted as the major strategy for restoration of degraded lands in the dry tropics.

http://dx.doi.org/10.1071/SR13265

Acknowledgements

We thank the Head and the Coordinator, Centre of Advanced Study in Botany, Department of Botany, for providing laboratory facilities. University Grants Commission, New Delhi, India provided financial support in form of University Research Fellowship to Mr Mahesh Kumar Singh.

Received 11 September 2013, accepted 5 December 2013, published online 31 March 2014

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Mahesh Kumar Singh (A) and Nandita Ghoshal (A,B)

(A) Centre of Advanced Study in Botany, Department of Botany, Banaras Hindu University, Varanasi, UP-221005, India.

(B) Corresponding author. Email: n_ghoshal@yahoo.co.in

Table 1. Microbial biomass C and N in the various land use types
(natural forest, NF; degraded forest, DF; agroecosystem, AG; Jatropha
plantation, JP) across the upper, middle and lower soil layers

Values are mean [+ or -] s.e. of all sampling dates of the first and
second annual cycles. Within rows, means followed by the same lower
case letter are not significantly different at P=0.05; within
columns, means followed by the same upper case letter are not
significantly different at P=0.05; l.s.d. values are at P=0.05

                        Microbial biomass C

                  Rainy                    Winter


                               0-10cm

NF       353.61aC [+ or -] 13.08   567.65bC [+ or -] 27.19
DF       268.84aA [+ or -] 18.56   345.62bA [+ or -] 15.93
AG       253.24aA [+ or -] 8.97    322.08bA [+ or -] 15.94
JP       306.75aB [+ or -] 9.35    425.00bB [+ or -] 11.94
l.s.d.            27.27                     38.88

                              10-20 cm

NF       211.55aC [+ or -] 9.50    324.35bB [+ or -] 13.54
DF       182.21aB [+ or -] 6.91    298.80bB [+ or -] 18.73
AG       127.30aA [+ or -] 10.19   213.88bA [+ or -] 21.07
JP       190.67aB [+ or -] 8.20    312.64bB [+ or -] 13.06
l.s.d.            18.34                     35.35

                              20-30 cm

NF       136.38aB [+ or -] 9.25    266.64bC [+ or -] 17.19
DF       106.21aA [+ or -] 8.57    210.06bB [+ or -] 14.83
AG        95.27aA [+ or -] 6.81    132.76bA [+ or -] 13.57
JP       124.36aB [+ or -] 6.81    251.99bC [+ or -] 9.65
l.s.d.            16.55                     29.36

                Microbial biomass C

                  Summer            l.s.d.

NF       709.55cD [+ or -] 34.23    56.15
DF       443.71cB [+ or -] 18.89    38.03
AG       351.40bA [+ or -] 20.90    34.18
JP       524.63cC [+ or -] 24.69    35.66
l.s.d.            52.93

                      10-20 cm

NF        463.73cC [+ or -] 36.63    49.46
DF       348.09cAB [+ or -] 20.02    34.79
AG        298.59cA [+ or -] 21.11    38.79
JP        380.90cB [+ or -] 25.38    36.54
l.s.d.            55.51

                      20-30 cm

NF       378.39cC [+ or -] 22.32    36.49
DF       300.89cB [+ or -] 30.11    42.62
AG       231.56cA [+ or -] 24.42    35.38
JP       323.72cB [+ or -] 21.95    30.67
l.s.d.            51.97

                       Microbial biomass N

                 Rainy                   Winter

NF       43.90aC [+ or -] 0.90    66.37bD [+ or -] 3.30
DF       36.30aB [+ or -] 2.24    42.86bB [+ or -] 2.47
AG       29.38aA [+ or -] 1.76    36.99bA [+ or -] 1.18
JP       38.37aB [+ or -] 1.26    55.65bC [+ or -] 2.26
l.s.d.            3.38                    5.21

                            10-20 cm

NF       14.86aB [+ or -] 0.90    26.96bC [+ or -] 2.14
DF       10.72aA [+ or -] 0.90    18.67bB [+ or -] 1.83
AG        9.33aA [+ or -] 0.66    11.75aA [+ or -] 0.98
JP       11.41aA [+ or -] 1.26    20.74bB [+ or -] 1.83
l.s.d.            1.99                    4.85

                            20-30 cm

NF        7.26aC [+ or -] 0.67    l6.94bC [+ or -] 1.40
DF       4.84aAB [+ or -] 0.42     6.57aA [+ or -] 0.50
AG        3.46aA [+ or -] 0.32     4.84aA [+ or -] 0.38
JP       5.88aBC [+ or -] 0.50    11.06aB [+ or -] 1.14
l.s.d.            1.48                    2.52

               Microbial biomass N

                 Summer           l.s.d.

NF       81.93cD [+ or -] 2.24     5.03
DF       52.20cB [+ or -] 2.32     5.00
AG       42.52cA [+ or -] 3.l9     4.71
JP       67.75cC [+ or -] 3.09     5.18
l.s.d.            5.73

                     10-20 cm

NF       52.89cC [+ or -] 1.97     3.75
DF       40.44cB [+ or -] 2.81     5.03
AG       23.16bA [+ or -] 2.18     5.34
JP       44.59cB [+ or -] 2.37     4.80
l.s.d.            6.15

                     20-30 cm

NF        31.11cB [+ or -] 2.14    6.60
DF       21.78bAB [+ or -] 2.07    6.38
AG        15.56bA [+ or -] 1.39    4.85
JP       25.58bAB [+ or -] 1.83    6.24
l.s.d.            9.84

Table 2. Univariate analysis of variance for microbial biomass C
(MBC) and N (MBN) according to site, season, depth and interactions

* P < 0.05; ** P < 0.01; *** P < 0.001; n.s., not significant

Independent variables   d.f.              F

                                  MBC          MBN

Site                     3     217.97 ***   176.71 ***
Season                   2     665.37 ***    1373 ***
Depth                    2     694.58 ***   556.11 ***
Site x season            6     21.49 ***    15.95 ***
Site x depth             6     17.36 ***    19.02 ***
Season x depth           4     0.85 (ns)    16.27 ***
Site x season x depth    12     3.67 **       1.95 *

Table 3. Microbial biomass C/N ratio across the various land use
types (natural forest, NF; degraded forest, DF; agroecosystem, AG;
Jatropha plantation, JP) in the upper, middle and lower layer

Values are mean [+ or -] s.e. of all sampling dates of the first and
second annual cycles. Within rows, means followed by the same lower
case letter are not significantly different at P = 0.05; within
columns, means followed by the same uppercase letter are not
significantly different at P = 0.05

                             Land use types
Soil depth
(cm)                  NF                       DF

0-10         8.46abA [+ or -] 0.22    8.05abA [+ or -] 0.25
10-20        1l.75aB [+ or -] 0.62   14.30abB [+ or -] 1.15
20-30        15.97aC [+ or -] 0.91   24.00bcC [+ or -] 2.39
l.s.d.               1.83                     4.37
  (P=0.05)

                              Land use types
Soil depth                                                     l.s.d.
(cm)                  AG                       JP             (P=0.05)

0-10          8.62bA [+ or -] 0.30     7.81aA [+ or -] 0.13     0.66
10-20        15.33bB [+ or -] 0.89   13.86abB [+ or -] 1.12     2.74
20-30        25.97cC [+ or -] 2.76   19.82abC [+ or -] 1.44     5.69
l.s.d.               4.79                     3.00
  (P=0.05)

Table 4. Correlation coefficients (r) showing relationships between
microbial biomass C or N and soil moisture content (MC) and soil
temperature (T) for land-use types: natural forest (NF), degraded
forest (DF), agroecosystem (AG) and Jutropha plantation (JP)

* P < 0.05; ** P < 0.01; n = 18 for each parameter of individual land
use type

Land use              MBC                         MBN
types
            MC (%)    T ([degrees]C)    MC (%)    T ([degrees]C)

NF         -0.74 **        0.31        -0.62 **        0.31
DF         -0.80 **        0.37        -0.56 *         0.42
AG         -0.55 *         0.37        -0.37           0.29
JP         -0.79 **        0.36        -0.62 **        0.38
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Author:Singh, Mahesh Kumar; Ghoshal, Nandita
Publication:Soil Research
Article Type:Report
Geographic Code:9INDI
Date:May 1, 2014
Words:6408
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