Variations In Soil Microbial Biomass Research Articles

Lichen biocrusts contribute to soil microbial biomass carbon in the northern temperate zone: A meta‐analysis

AbstractBiological soil crusts (biocrusts) have crucial ecological functions in dryland ecosystems, yet understanding the variations in soil microbial biomass within biocrusts across diverse ecosystems, climates and soil conditions remains limited. This knowledge gap constrains our understanding of how microbial communities within biocrusts regulate terrestrial carbon and nitrogen cycling. Hence, we conducted a meta‐analysis using 255 paired observations from 42 study sites across the northern temperate ecosystem. The analysis revealed that biocrusts harbour significantly higher soil microbial biomass carbon and nitrogen (SMBC and SMBN, respectively) levels than bare (non‐biocrust) soil across all habitat types. Notably, deeper soil layers (5–10 and >10 cm) accumulated less SMBC and SMBN than biocrust and biocrust–5‐cm soil, revealing that biocrusts influence shallow soil environments. Ecosystem type, soil texture, depth and season emerged as key factors influencing the distribution of SMBC within biocrusts. Of particular interest, lichen biocrusts accumulated the most SMBC compared with other biocrust types. Furthermore, the difference in SMBC between biocrust and non‐biocrust soils was more pronounced in oligotrophic habitats (e.g., desert, grassland, sand and sandy loam soils) than in eutrophic habitats (e.g., forest and loam soils). Random forest analysis confirmed that soil variables affected SMBC accumulation in biocrusts more than climatic factors. Soil organic carbon (SOC), as the primary source of SMBC, could be the most important determinant. Moreover, the disparity between non‐biocrust SMBC and biocrust SMBC increased with increasing mean annual temperature (MAT) or decreasing altitude. These insights underscore the substantial contribution of lichen biocrusts to SMBC and emphasize the need to incorporate this knowledge into regional models for predicting the effects of climate change on soil carbon budgets within biocrust microbiomes in temperate ecosystems of the Northern Hemisphere.

Drought-induced turnover of soil microbial biomass increases nutrient subsidies for the reproduction of tropical forest

El Niño-induced drought, which is intensified by climate change, can have huge impacts on soil microbial biomass and plant productivity in tropical forests. We tested whether drought-induced turnover of soil microbial biomass can be a potential source of phosphorus (P), the limiting nutrient, for the reproduction of tropical forest trees (mast fruiting). We measured the seasonal variations in soil microbial biomass P and soil solution P concentrations including the periods before and after drought in a dipterocarp forest in Indonesia. Drought resulted in a decrease in soil microbial biomass C, N, and P, followed by a recovery after re-wetting. There was a sharp peak of soil solution P concentrations during the drought. The significant difference between soil microbial biomass P before and after drought amounted to 2.0 kg P ha−1. The potential P release from microbial turnover is not negligible compared to the additional P demand for fruit production (1.0 kg P ha−1) as well as the annual demand for litter production (2.5 kg P ha−1 year−1). In addition to the accumulation of nutrients for several non-fruiting years and their re-distribution in tree biomass, drought-induced microbial turnover can be nutrient subsidies for dipterocarp reproduction in highly-weathered soils.

Effects of warming on the stoichiometry of soil microbial biomass and extracellular enzymes in an alpine shrubland

The alpine shrublands on the Qinghai-Tibetan Plateau are experiencing significant warming. Revealing the effects of warming on the soil microbial metabolism will provide insights into the dynamics of soil carbon (C) and nutrient cycling in these alpine ecosystems. A five-year warming experiment (+1.3 °C, using open-top chambers) was conducted in a Sibiraea angustata-dominated alpine shrubland on the eastern Qinghai-Tibetan Plateau. We examined the effects of warming on the stoichiometry of topsoil (0–15 cm) microbial biomass, extracellular enzyme activity and their relationships with soil physicochemical properties. The results showed that the effects of warming on the soil microbial biomass C, nitrogen (N) and phosphorus (P) varied with the growing season. Warming increased the activity levels of C-acquiring enzymes (β-glucosidase, BG) by 7.5 %-15.1 % throughout the growing season (P < 0.01) and the activity of polyphenol oxidase (PPO) by 6.5 % during the early growing season (P < 0.05), indicating that warming would strengthen microbial C limitation and increase degradation of soil labile and recalcitrant C components. Warming increased the activity of P-acquiring enzyme (acid phosphatase, AP) by 14.6 % (P < 0.01) and triggered microbial P limitation during the late growing season, which might be a result of an increasing alpine shrub P uptake. Warming did not affect the total activity levels of N-acquiring enzymes throughout the growing season (P > 0.05), mainly due to higher soil N availability. Warming did not affect the stoichiometry of soil extracellular enzymes throughout the growing season (P > 0.05), except for a decreasing in the enzyme N:P ratio during the early growing season (P < 0.05). Moreover, the microclimate (air and soil temperature), available soil nutrients (soil dissolved organic C and available P) and soil pH accounted for most of the variation in soil microbial biomass, extracellular enzyme activity and their stoichiometry in response to warming. Our results suggest that warming may trigger and strengthen soil microbial C and P limitation during the growing season, accelerating soil C loss and nutrient cycling in alpine shrublands on the Qinghai-Tibetan Plateau.

The validity of ecological hypotheses concerning aboveground organisms for soil microbial biomass and diversity across soil depths on the Mongolian Plateau

Although many empirical hypotheses have been proposed and tested to explain the biomass and diversity of aboveground organisms, these hypotheses have not been tested for soil microorganisms across soil depths. Here, we determined the ability of hypotheses concerning physiological tolerance, plant energy, soil energy, and habitat heterogeneity to explain the variance in microbial biomass (as determined by phospholipid fatty acid) and diversity (as determined by high-throughput sequencing) in surface (0–20 cm) and deep (40–60 cm) soil layers on the Mongolian Plateau. We found that aboveground net primary production (ANPP) and plant species richness steeply declined as aridity values increased. Physiological tolerance and habitat heterogeneity explained the spatial variation in ANPP while physiological tolerance and soil energy explained the spatial variation in plant diversity. The relationships between aridity and microbial variables differed between soil layers or microbial groups. Aridity values had hump-shaped relationships with surface-soil bacterial biomass or diversity but had linear and negative relationships with surface-soil fungal biomass or diversity. Aridity values were linearly and negatively related with deep-soil bacterial or fungal biomass but were unrelated with deep-soil bacterial or fungal diversity. We also found the ability of the ecological hypotheses to explain the variances in microbial variables (biomass and diversity) diffed between soil layers or microbial groups on the Mongolia Plateau. The surface-soil bacterial biomass was mainly associated with plant energy and physiological tolerance while surface-soil bacterial diversity was mainly associated with habitat heterogeneity and physiological tolerance; surface-soil fungal biomass and diversity were mainly associated with habitat heterogeneity and physiological tolerance. The deep-soil bacterial biomass and diversity were mainly associated with physiological tolerance and soil energy; deep-soil fungal biomass was mainly associated with plant energy and physiological tolerance while deep-soil fungal diversity was mainly associated with soil energy and habitat heterogeneity. Our results showed that the major ecological hypotheses traditionally applied to plant communities can explain much of the variation in soil microbial biomass and diversity. These findings that identifying ability of ecological hypotheses to explain the variance in both plant and microbial biomass and diversity will be crucial importance to understand biodiversity assembly under ongoing environmental changes.

Soil properties and climate affect arbuscular mycorrhizal fungi and soil microbial communities in Mediterranean rainfed cereal cropping systems

Soil microorganisms are generally considered sensitive indicators of soil health and fertility. Understanding the role of environmental factors in driving soil microorganisms’ distributions is vital for sustainable crop production, particularly in vulnerable agricultural systems. This study aims to investigate the effect of environmental factors on the variation of soil microbial biomass and arbuscular mycorrhizal (AM) fungi in Mediterranean rainfed cereal systems. To do so, plant roots and soil were sampled from three cereal crops: Avena sativa L., Hordeum vulgare L. and Triticum turgidum L. growing in 24 rainfed sites from three different bioclimatic zones (sub-humid, superior semi-arid and middle semi-arid) in northern Tunisia. Soil microbial phospholipid fatty acids (PLFA) fingerprints, percentage of root length colonized by AM fungi as well as AM fungal spore density were then assessed. The redundancy analysis (RDA) revealed that soil organic matter (SOM), temperature, altitude and soil sand content accounted for 22.7 % of the variation of the microbial PLFA profiles used to estimate both soil microbial biomass and their distribution across different microbial groups. These environmental factors were the most important drivers affecting bacterial PLFAs. However, no significant relationships were observed between fungal PLFAs and environmental factors. Mycorrhizal colonization differed significantly among the different host species and regions. The RDA results indicated that environmental factors, in particular mean annual precipitation (MAP), pH, available phosphorus (P) and carbon/ nitrogen ratio (C/N) explained 44.8 % of AM fungal root colonization and spore number variation. Mycorrhizal colonization was positively correlated with pH but negatively with P, C/N and MAP. Concerning AM fungal spore number, it was positively linked to P and MAP. In contrast, it was inversely related to soil pH. Highlighting the main edaphic and climatic factors disturbing soil microorganisms, especially AM fungi, helps to better understand how environmental change will influence soil microbial communities in Mediterranean rainfed cereal systems.

Tillage, Mulching and Nitrogen Fertilization Differentially Affects Soil Microbial Biomass, Microbial Populations and Bacterial Diversity in a Maize Cropping System

Determination of biologically active components of the soil organic matter, such as soil microbial biomass carbon (C) and nitrogen (N) can be used as indicators for variations in soil productivity due to changes in soil management. Soil agronomic management practices bring about changes in the physical and chemical properties of the soil, resulting in variations in soil microbial biomass and microbial diversity. The effects of tillage, mulch and inorganic fertilizers on soil microbial biomass C and N, microbial populations and bacterial diversity were determined from the treatment combinations which had been applied for 5 years in Central Kenyan Highlands. The test crop used was maize (Zea mays L.). The study involved conventional and minimum tillage systems, mulching and inorganic fertilizers (120 kg N/ha). Tillage (P &amp;lt; 0.001), mulch (P &amp;lt; 0.001), and fertilizer (P = 0.009) significantly affected soil microbial biomass C and N whereby minimum tillage and mulch increased soil microbial biomass C and N. Interestingly, minimum tillage and mulch recorded the highest bacteria and fungi CFUs compared to conventional tillage and inorganic fertilizers. Only fertilizer and mulch (P &amp;lt; 0.001) had significant effect on actinobacteria CFUs. Amplified ribosomal DNA analysis (ARDRA) showed that the highest genetic distance of 0.611 was recorded between treatments conventional tillage + no mulch + no NPK fertilizer and conventional tillage + no mulch + NPK fertilizer. The results demonstrate that minimum tillage and mulching are attractive soil agronomic management practices since they increase soil microbial biomass and bacterial diversity in agricultural soils.

Contribution of root traits to variations in soil microbial biomass and community composition

It is well known that plant root-microbe interactions are critical drivers of ecosystem processes such as soil carbon and nutrient cycling; however, considerable uncertainties exist about how root chemical and morphological traits influence soil microbial community composition. We used 13 tree species grown in field monocultures in subtropical China to explore the ecological linkages between leaves, leaf litter, and root chemical and morphological traits associated with plant growth and nutrient-acquisition strategies, as well as soil microbial biomass, the fungi to bacteria (F/B) ratio, and Gram-positive to Gram-negative bacteria (GP/GN) ratio. The combination of above- and belowground traits captured a greater proportion of variations in soil microbial biomass and community composition than did aboveground traits alone. Individually, root traits explained more variations of the F/B and GP/GN ratios than did the individual effects of aboveground leaf or leaf litter traits. All distinct microbial biomass groups and F/B ratios decreased with the specific root length, whereas the F/B ratio increased, and the GP/GN ratio decreased with root tissue density. Our study highlighted the importance of the functional traits of plant roots in determining the microbial biomass and community composition in forest ecosystems. The combination of leaf and root traits may improve our understanding of the mechanisms that underly plant-microbe interactions toward the sustainable management of forest ecosystems.

Effects of Different Ages of Robinia pseudoacacia Plantations on Soil Physiochemical Properties and Microbial Communities

Robinia pseudoacacia is widely planted on the Loess Plateau as a strong drought-tolerant and salt-tolerant species for vegetation restoration. However, this mode of pure plantation has triggered great concern over the soil ecosystem. The aim of this study was to explore the effects of the plantation on soil physiochemical properties, soil microorganisms, and the relationship between them in Robinia pseudoacacia plantations of different ages. Four different ages of Robinia pseudoacacia stands, including 10-year-old, 15-year-old, 25-year-old, and 40-year-old (abbreviated as Y10, Y15, Y25, and Y40, respectively) were selected, and 20 soil physicochemical and biological indicators were determined. The variation in soil microbial biomass was influenced by sampling depth, and consistent with the variations in TN (soil total nitrogen) and SOC (soil organic carbon) during 25 years’ artificial forestation. Soil moisture increased significantly at Y15 and then decreased at Y40 but other soil properties remained relatively stable. The contents of phosphor lipid fatty acid (PLFA) of different microbial groups followed the order of B (Bacteria) &gt; G− (Gram-negative) &gt; G+ (Gram-positive) &gt; A (Actinomycetes) &gt; F (Fungi). The ratios of F/B (Fungi to Bacteria) and Sat/Mono (Saturated PLFAs to Monosaturated PLFAs) of different ages of plantations showed a similar trend, i.e., declined first, then rose, and declined again. The ratios of Cy/Pre (Cyclopropyl PLFAs to Precursor PLFAs) and G+/G− (Gram-positive to Gram-negative) of the soil of all ages of plantations showed a trend of slow growth and a trend of rapid growth, respectively. Redundancy analysis showed that the contents of individual PLFAs and total PLFA were positively correlated with SOC and TN, but variations of soil PLFA ratios mostly depended on other soil properties. After artificial forestation, the ratios of F/B and Sat/Mono were lower than before forestation, while the ratio of Cy/Pre varied with different soil layers. The ratio of G+/G− increased with the increase in afforestation time, peaking at the 25th year. The contents of individual PLFAs and total PLFA may be sensitive indicators of SOC and TN within 25 years’ plantation. Lower ratio of F/B and higher G+/G− suggest that the sustainability of the ecosystem is weaker and the fertility of the soil is lower after plantation of Robinia pseudoacacia.

Change in soil microbial biomass and regulating factors in an alpine meadow site on the Qinghai-Tibetan Plateau

ABSTRACT The change in soil microbial biomass (SMB) content and its direct links to soil organic matter (SOM) and environmental factors are not well understood for high-elevation regions. Therefore, this research investigated the temporal variation of SMB and its relationship with SOM and environmental factors in an alpine meadow site on the Qinghai-Tibetan Plateau. The soil organic carbon (SOC) and total nitrogen (TN) contents in alpine meadows showed monthly and seasonal variations and were higher in colder months, and the soil C/N ratio was higher in winter and in autumn than it was in the other seasons (P < 0.05). In addition, the changes in the SMB C and SMB N contents were notable at monthly and seasonal scales, whereas the SMB C and SMB N contents were higher in the winter and spring than they were in the other seasons (P < 0.05); the ratio of SMB C/SOC was higher in spring than it was in the other seasons; the ratio of the SMB N/TN content was higher in cold or cool months than it was in the other months; and the ratio of the SMB C/SMB N was highest in August (P < 0.05). Moreover, the SMB C and SMB N contents were significantly positively correlated to the SOC and TN contents (P < 0.01), and the SMB content was also significantly positively correlated to soil water content and air temperature (P < 0.05), or to soil bulk density and soil pH (P < 0.05). The results suggested that the change in the SMB in the alpine meadows was highly regulated by the SOC and TN and by monthly and seasonal changes in the soil bulk density, the soil pH, soil moisture, and air temperatures.

Seasonal dynamics of soil microbial biomass C and N of Keteleeria fortunei var. cyclolepis forests with different ages

Soil microbial biomass is an important indicator to measure the dynamic changes of soil carbon pool. It is of great significance to understand the dynamics of soil microbial biomass in plantation for rational management and cultivation of plantation. In order to explore the temporal dynamics and influencing factors of soil microbial biomass of Keteleeria fortunei var. cyclolepis at different stand ages, the plantation of different ages (young forest, 5 years; middle-aged forest, 22 years; mature forest, 40 years) at the Guangxi Daguishan forest station of China were studied to examine the seasonal variation of their microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) by chloroform fumigation extraction method. It was found that among the forests of different age, MBC and MBN differed significantly in the 0–10 cm soil layer, and MBN differed significantly in the 10–20 cm soil layer, but there was no significant difference in MBC for the 10–20 cm soil layer or in either MBC or MBN for the 20–40 cm soil layer. With increasing maturity of the forest, MBC gradually decreased in the 0–10 cm soil layer and increased firstly and then decreased in the 10–20 cm and 20–40 cm soil layers, and MBN increased firstly and then decreased in all three soil layers. As the soil depth increased, both MBC and MBN gradually decreased for all three forests. The MBC and MBN basically had the same seasonal variation in all three soil layers of all three forests, i.e., high in the summer and low in the winter. Correlation analysis showed that MBC was significantly positively correlated with soil organic matter, total nitrogen, and soil moisture, whereas MBN was significantly positively correlated with soil total nitrogen. It showed that soil moisture content was the main factor determining the variation of soil microbial biomass by Redundancy analysis. The results showed that the soil properties changed continuously as the young forest grew into the middle-aged forest, which increased soil microbial biomass and enriched the soil nutrients. However, the soil microbial biomass declined as the middle-age forest continued to grow, and the soil nutrients were reduced in the mature forest.

Spatial variation in soil microbial community structure and its relation to plant distribution and local environments following afforestation in central China

Land use change directly influences soil microbial communities by altering vegetation cover. However, how soil microbial community structure responds spatially to plant distribution within a land use type following afforestation remains unclear. Here, we investigated the spatial variations in soil microbial biomass [e.g., bacteria (B), fungi (F), gram-positive bacteria (G+), and gram-negative bacteria (G−)] and community composition (the F:B ratio and G+:G- ratio) in woodland, shrubland and adjacent open areas (i.e., control) in the Danjiangkou Reservoir of central China, using geostatistical methods and phospholipid fatty acid (PLFA) analysis. We also explored the underlying mechanisms of whether or not and how environmental drivers, including biotic factors (e.g., tree distribution, present litter and root biomass) and abiotic factors [e.g., soil organic carbon (SOC) and total nitrogen (TN), soil pH, and soil moisture], regulated the spatial variations in these microbial properties using partial Mantel tests. Afforestation increased the PLFA content and the G+:G- ratio but reduced the F:B ratio compared to that of the open area. Spatial analysis revealed that spatial variations in microbial communities were governed by local environmental drivers affected by tree distribution. Generally, SOC was a critical control on microbial biomass and community composition in all land use types, but the major drivers varied with land use type. Soil pH, SOC and TN affected almost all types of microbial PLFAs in shrubland, whereas litter biomass, SOC and TN were selectively correlated with specific groups of PLFAs (mainly from bacteria) in woodland. Soil pH affected the F:B ratio rather than the G+:G- ratio in both woodland and shrubland, while root biomass, SOC and TN were proved to be determinants of the F:B ratio and G+:G- ratio in shrubland. Other than SOC, the soil pH and N level were the primary controls on spatial variations in microbial biomass following afforestation. Overall, our results revealed that tree distribution-induced shifts in local environments controlled the spatial variations in soil microbial community structure within one land use type, highlighting that the role of spatial heterogeneity in microbial communities has important implications for land management.

Land use change: A key ecological disturbance declines soil microbial biomass in dry tropical uplands

Land use changes such as transformation of natural landscapes, forest degradation and increase in croplands due to human activities are considered amongst the most influential ecological disturbances affecting soil, ecosystems and environmental sustainability. The previous works from India are limited to show that soil disturbances influence abiotic and biotic factors along a rural–urban gradient. However, variations in soil microbial biomass (SMB) –C, –N and –P quantity due to land use changes at different soil depths across different land use types remain poorly understood on comparative ground. We investigated the impact of land use types on soil properties and SMB –C, –N and –P levels across different soil depths (0–10, 10–20 and 20–30 cm) in dry tropical uplands. Four land use types/covers (natural forest, mixed forest, savanna and agriculture land) were selected. The present study is based on two hypotheses: i) different land use types affect SMB levels in top surface soil (0–10 cm), but have less effects in deeper soil profiles (20–30 cm); and ii) SMB levels in top surface soil are highest in natural forest, followed by mixed forest and then savanna and agriculture lands. ANOVA showed significant differences in SMB values due to land use covers (P < 0.001), soil depths (P < 0.001) and land use types × soil depths interaction (P < 0.001). Although, there had no effect of land use types on SMB levels in deeper soil profiles (20–30 cm) but soil parameters (soil pH, soil moisture, soil temperature, total-N, C/N ratio and organic-C) significantly affect SMB levels in top surface (0–10 cm) soil. The study suggests that SMB may be considered as a key indicator of soil fertility index, while land use practices are a major cause for loss of microbial community composition/biomass in dry tropical upland soil.

Soil microbial biomass, phosphatase and their relationships with phosphorus turnover under mixed inorganic and organic nitrogen addition in a Larix gmelinii plantation

Atmospheric nitrogen (N) deposition can affect soil microbial biomass, phosphatase activity, and the concentrations of organic phosphorus (P), inorganic P and available P, but the changes in soil microbial biomass under mixed inorganic and organic N addition and their relationships with soil P turnover in forest ecosystems are not fully understood. In this study, a simulated N deposition experiment was conducted in a Larix gmelinii plantation in Northeastern China to investigate the variation of soil microbial biomass, phosphatase activity, P forms and available P concentrations as well as the relationships between these features. The experiment was arranged in a randomized block design with three replications for each treatment, including the control (no N addition, CK), total inorganic N (NH4NO3, TIN), mixed inorganic and organic N (inorganic N and organic N in the ratio of 7:3, ION), and total organic N (urea and glycine 1:1, TON). The results indicated that there was a significant difference in the response of soil biochemical characteristics to different types of N addition. Soil total microbial biomass, the biomass of bacteria and actinomycetes, alkaline phosphomonoesterase (AlP) activity, as well as oxalate-extracted aluminum (Al), cMonoesters, cDiesters and orthophosphate concentrations were significantly increased by the addition of mixed inorganic and organic N, whereas they were not affected by single inorganic or organic N addition. Compared to the CK treatment, the increase in soil microbial biomass and Al oxides concentrations under ION treatment significantly increased soil cMonoesters and cDiesters concentrations, and the increased bacterial biomass contributed to the increase of soil AlP activity. Moreover, the ION treatment also significantly increased soil total P concentration and enhanced microbial immobilization of P compared to the CK treatment. However, there was no significant difference in available P concentration between the ION treatment and other treatments, which could be attributed to increased orthophosphate concentration under the ION treatment. Overall, the findings suggest that bacteria and AlP can play important roles in maintaining soil P availability by accelerating P turnover under conditions of increased atmospheric N deposition in a Larix gmelinii plantation.

Spatio-temporal variation in soil microbial biomass and enzymatic activity in different forest ecosystem of North-India

Background &amp; Aim: The present study compared the soil microbial biomass, enzymatic activity and the nutrientaccessibility under different location covering dry deciduous and temperate forest of North-India. Also, the temporalvariation was evaluated for two consecutive years during the pre and post monsoon season. Results: The resultsindicated significant temporal and spatial variation among the soil characteristics and the availability of nutrients. Soilmicrobial biomass carbon, nitrogen and phosphorous ranged from 151.63 - 471.1, 36.56 - 88.68 and 15.73 - 62.18 μgg-1. Acid phosphatese activity was highest in forest stand 4 and lowest in forest stand 1, while the value of β-glucosidase activity was recorded maximum at forest stand 5 i.e. 1514.95 μg g-1 h-1 whereas the lower value was inforest stand 1 i.e. 582.23 μg g-1 h-1. Furthermore, the dehydrogenase(DHA) activity ranged from 38.61 - 497.78 μg g-1h-1 and 158.14 - 707.37 μg g-1 h-1 for the two seasons with lowest value at forest stand 1 and highest at forest stand 4.Similarly, the estimated protease and flurosceindiacetate (FDA) activity was high at forest stand 4. Comparisonamong different soil properties was markedly higher during the pre-monsoon season and it decreases along the foreststand located in dry deciduous region during the study period. Conclusion: The higher microbial biomass andenzymatic activities at forest stand resides in temperate region suggested the higher nutrient availability and soilfertility in temperate forest

Variation of soil microbial biomass C and hydrolytic enzyme activities in a rangeland ecosystem: are slope aspect and position effective?

This study was conducted to investigate the effects of slope aspect and position on microbial biomass C (MBC) and some hydrolytic enzyme activities involved in soil N, P, and S cycles in a rangeland ecosystem of west central Iran. Soil samples were collected from three slope positions (summit, backslope, and footslope) of contiguous north- and south-facing slopes. Results indicated higher silt and clay content, soil organic C (SOC), total N (TN), and C/N ratio on the north-facing slope. Furthermore, MBC, alkaline phosphomonoesterase (ALP), acid phosphomonoesterase (ACP), arylsulfatase (ARS), urease (URS), L-asparaginase (LAS), and L-glutaminase (LGL) activities were greater by 46.1, 65.9, 58.6, 59.6, 52.6, 62.8, and 65.7%, respectively, on the north-facing slope compared to the south-facing one. Higher ratios of enzyme activities to MBC were observed on the north-facing slope. In contrast, per cent of inorganic N and microbial quotient were greater on the south-facing slope. The activity of ALP, ACP, ARS along with SOC, TN, and MBC values decreased from summit to footslope. Overall, our findings indicate that north-facing slope and summit position support greater microbial biomass and hydrolytic diversity.

Effects of application of corn straw on soil microbial community structure during the maize growing season

This study investigated the influence of corn straw application on soil microbial communities and the relationship between such communities and soil properties in black soil. The crop used in this study was maize (Zea mays L.). The five treatments consisted of applying a gradient (50, 100, 150, and 200%) of shattered corn straw residue to the soil. Soil samples were taken from May through September during the 2012 maize growing season. The microbial community structure was determined using phospholipid fatty acid (PLFA) analysis. Our results revealed that the application of corn straw influenced the soil properties and increased the soil organic carbon and total nitrogen. Applying corn straw to fields also influenced the variation in soil microbial biomass and community composition, which is consistent with the variations found in soil total nitrogen (TN) and soil respiration (SR). However, the soil carbon-to-nitrogen ratio had no effect on soil microbial communities. The abundance of PLFAs, TN, and SR was higher in C1.5 than those in other treatments, suggesting that the soil properties and soil microbial community composition were affected positively by the application of corn straw to black soil. A Principal Component Analysis indicated that soil microbial communities were different in the straw decomposition processes. Moreover, the soil microbial communities from C1.5 were significantly different from those of CK (p < 0.05). We also found a high ratio of fungal-to-bacterial PLFAs in black soil and significant variations in the ratio of monounsaturated-to-branched fatty acids with different straw treatments that correlated with SR (p < 0.05). These results indicated that the application of corn straw positively influences soil properties and soil microbial communities and that these properties affect these communities. The individual PLFA signatures were sensitive indicators that reflected the changes in the soil environment condition.

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

The impact of land-use change on soil microbial biomass carbon (C) and nitrogen (N) was studied through two annual cycles involving natural forest, degraded forest, agroecosystem and Jatropha curcas plantation. Soil microbial biomass C and N, soil moisture content and soil temperature were analysed at upper (0–10 cm), middle (10–20 cm) and lower (20–30 cm) soil depths during the rainy, winter and summer seasons. The levels of microbial biomass C and N were highest in the natural forest, followed in decreasing order by Jatropha curcas plantation, degraded forest and the agroecosystem. The highest level of soil microbial biomass C and N was observed during summer, decreasing through winter to the minimum during the rainy season. Soil microbial biomass C and N decreased with increasing soil depth for all land-use types, and for all seasons. Seasonal variation in soil microbial biomass was better correlated with the soil moisture content than with soil temperature. The microbial biomass C/N ratio increased with the soil depth for all land-use types, indicating changes in the microbial community with soil depth. It is concluded that the change in land-use pattern, from natural forest to other ecosystems, results in a considerable decrease in soil microbial biomass C and N. Jatropha plantation may be an alternative for the restoration of degraded lands in the dry tropics.

Seasonal dynamics of soil microbial biomass C shows close correlation with environmental factors in natural Fagus crenata forests

Soil microbial biomass (Cmic) is an important factor regulating a number of ecosystem processes. In this study, we investigated seasonal variations in soil microbial biomass in natural climax beech (Fagus crenata) forests in a typical cold-temperate mountain region of Japan. Four permanent tower sites along an altitudinal gradient were selected and soil samples were collected once every month during the growing season of 2007. Soil microbial biomass (by fumigation-extraction method) and soil properties were later measured in the laboratory, while environmental factors (soil temperature, soil moisture) were continuously recorded in the field. Our results indicated large seasonal variations (130.4 ~ 5558.0 µg g−1) in soil microbial biomass in beech forests – a range that is much larger than previously reported. Statistically significant correlations are noted between soil properties with Cmic, but largely due to spatial linkages. On the other hand, the environmental factors of soil temperature and especially soil moisture largely control seasonal variations in Cmic. Furthermore, pH could be an important factor influencing seasonal change in Cmic at the 20–30 cm deep soil layer. The study suggests no direct correlation between plant eco-physiology and soil microbial biomass in seasonal courses of the forests.

SEASONAL AND TEMPORAL VARIATION IN SOIL MICROBIAL BIOMASS C, N AND P IN DIFFERENT TYPES LAND USES OF DRY DECIDUOUS FOREST ECOSYSTEM OF UDAIPUR, RAJASTHAN, WESTERN INDIA

The soil microbial biomass of soil is being increa sing recognized as sensitive indicator of soil quality. Its knowledge is fundamental for sustainab le environment management. The soil microbial biomass C, N and P were studied in four different l and uses of dry tropical forest of Udaipur, Rajasth an, Western India to assess the influence of abiotic, p hysico-chemical variables and difference in differe nt land uses (mixed forest, butea plantation, grasslan d and agricultural lands) on the seasonal variation in soil microbial biomass. Microbial biomass C, N and P were highest during rainy season and lowest durin g winter in all the four different land use with the exception of microbial N which was lowest in summer in mixed forest and butea plantation. Microbial biomas s C and N were shown to be significantly correlated to the abiotic and physico-chemical variables of th e soil, such as soil temperature, relative humidity , soil moisture, organic C, total N, clay, and pH. Present study clearly shows that land use has a significan t effect on microbial biomass C, N and P in soil by a ltering natural soil characteristics under the same ecological conditions.

Soil microbial community composition under Eucalyptus plantations of different age in subtropical China

Eucalyptus is one of the fastest growing woody plants in the world, but few studies have reported the soil microbial community composition in Eucalyptus ecosystems. This study investigated the soil microbial communities in plantations of 3-, 7-, 10- and 13-year-old Eucalyptus in subtropical China based on phospholipid fatty acids (PLFA) analysis. The variation in soil microbial biomass and community compositions were influenced by sampling site and season and the interaction of both, which were consistent with the variation in soil total nitrogen (TN), soil organic carbon (SOC) and soil moisture. The number and abundances of PLFAs, and the amount of soil TN and SOC were higher in plantation of 13-year-old Eucalyptus than those in other younger plantations, suggesting that the soil properties and the soil microbial community composition is not negatively affected by the planting of Eucalyptus. The ratio of monounsaturated-to-branched fatty acids, the proportional abundance (mol%) of bacterial PLFA and fungal PLFA varied significantly with Eucalyptus plantations of different age, suggesting that the individual PLFA signatures might be sensitive indicators of soil properties associated with forest plantations.