Response Of Soil Microbial Biomass Research Articles

Nonbiodegradable microplastic types determine the diversity and structure of soil microbial communities: A meta-analysis

As an emerging contaminant, microplastics (MPs) have received considerable attention for their potential threat to the soil environment. However, the response of soil bacterial and fungal communities to MPs exposure remains unclear. In this study, we conducted a global meta-analysis of 95 publications and 2317 observations to assess the effects of nonbiodegradable MP properties and exposure conditions on soil microbial biomass, alpha and beta diversity, and community structure. Our results indicate that MPs increased (p < 0.05) soil active microbial biomass by 42%, with the effect varying with MPs type, exposure concentration, exposure time and soil pH. MPs concentration was identified as the most important factor controlling the response of soil microbial biomass to MPs. MPs addition decreased (p < 0.05) the soil bacterial Shannon and Chao1 indices by 2% and 3%, respectively, but had limited effects (p > 0.05) on soil fungal Shannon and Chao1 indices. The type of MPs and exposure time determined the effects of MPs on bacterial Shannon and Chao1 indices, while the type of MPs and soil pH controlled the response ratios of fungal Shannon and Chao1 indices to MPs. Specifically, soil organic carbon (SOC) was the major factor regulating the response ratio of bacterial alpha diversity index to MPs. The presence of MPs did not affect soil bacterial community structure and beta diversity. Our results highlight that MPs reduced bacterial diversity and richness but increased the soil active microbial biomass, suggesting that MPs could disrupt biogeochemical cycles by promoting the growth of specific microorganisms.

Soil nitrogen availability drives the response of soil microbial biomass to warming

Although soil microbial biomass responses to experimental warming have been extensively studied, the mechanisms through which elevated temperatures influence soil microbial biomass remain unclear. In this study, we performed a global meta-analysis to quantify the global pattern of soil microbial biomass in response to warming. Our findings suggest that global warming effect is not apparent when all the data are pooled together, while warming does increase microbial biomass under specific conditions (Δ°C ≥ 2 °C). This constructive influence is particularly accentuated under certain circumstances, including high precipitation levels (>800 mm), short treatment durations (<1 year), and within agricultural ecosystems. More importantly, our findings suggest that the impact of global warming on soil microbial biomass is largely mediated by changes in soil nitrogen availability. These findings underscore the pivotal role of nitrogen availability in modulating the response of soil microbial biomass to warming, while also emphasizing the intricate influence between multiple factors such as temperature, duration, and precipitation in shaping the patterns of warming effects.

Responses of soil microbial biomass, microbial entropy and soil-microorganism stoichiometry imbalance to different utilization patterns in the artificial grassland of karst desertification area

Different utilization patterns can alter the C, N, P cycles and their ecological stoichiometry characteristics in grassland soils. However, the effects of different utilization patterns on soil microbial biomass, microbial entropy and soil-microorganism stoichiometry imbalance of artificial grassland are not clear. So this study was took different utilization patterns of artificial grassland [i.e., grazing grassland (GG), mowing grassland (MG), enclosed grassland (EG)] as the research object to investigate responses of soil microbial biomass, microbial entropy and soil-microorganism stoichiometry imbalance to different utilization patterns in the karst rocky desertification control area. We found that the contents of microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) were highest in GG, and the content of microbial biomass phosphorus (MBP) was highest in EG. Soil microbial biomass entropy carbon (qMBC) and soil microbial biomass entropy nitrogen (qMBN) of GG and MG were higher than those of EG, but soil microbial biomass entropy phosphorus (qMBP) was opposite. C:N stoichiometry imbalance (C:Nimb) was EG &amp;gt; GG &amp;gt; MG, C:P stoichiometry imbalance (C:Pimb) was EG &amp;gt; MG &amp;gt; GG, N:P stoichiometry imbalance (N:Pimb) was MG &amp;gt; EG &amp;gt; GG. MBN was significantly positive correlated with C:Nimb and C:Pimb, MBC was significantly negative correlated with C:Pimb, MBP was significantly negative correlated with N:Pimb. The redundancy analysis (RDA) results showed that N:Pimb (p = 0.014), C:Nimb (p = 0.014), and C:P in the soil (C:Psoil, p = 0.028) had the most significant effect on microbial entropy. EG had a significant effect on soil microbial biomass and microbial entropy. The results of this study can directly or indirectly reflect the grassland soil quality under different utilization patterns in the karst rocky desertification area, which has a certain reference value for the degraded ecosystem restoration.

Differential responses of soil microbial biomass, diversity and interactions to land use intensity at a territorial scale

Impact of land use intensification on soil microbial communities across a territory remains poorly documented. Yet, it has to be deciphered to validate the results obtained at local and global scales by integrating the variations of environmental conditions and agricultural systems at a territorial scale. We investigated the impact of different land uses (from forest to agricultural systems) and associated soil management practices on soil molecular microbial biomass and diversity across a territory of 3300 km2 in Burgundy (France). Microbial biomass and diversity were determined by quantifying and high-throughput sequencing of soil DNA from 300 soils, respectively. Geostatistics were applied to map the soil macro-ecological patterns and variance partitioning analysis was used to rank the influence of soil physicochemical characteristics, land uses and associated practices on soil microbial communities. Geographical patterns differed between microbial biomass and diversity, emphasizing that distinct environmental drivers shaped these parameters. Soil microbial biomass was mainly driven by the soil organic carbon content and was significantly altered by agricultural land uses, with a loss of about 71 % from natural to agricultural ecosystems. The best predictors of bacterial and fungal richness were soil texture and pH, respectively. Microbial diversity was less sensitive than microbial biomass to land use intensification, and fungal richness appeared more impacted than bacteria. Co-occurrence network analysis of the interactions among microbial communities showed a decline of about 95 % of network complexity with land use intensification, which counterbalanced the weak response of microbial diversity. Grouping of the 147 cropland plots in four clusters according to their agricultural practices confirmed that microbial parameters exhibited different responses to soil management intensification, especially soil tillage and crop protection. Our results altogether allow evaluating the different levels of microbial parameters' vulnerability to land use intensity at a territorial scale.

Responses of soil microbial biomass C:N:P stoichiometry to increased precipitation and nitrogen deposition in temperate shrublands

Increased precipitation and nitrogen (N) deposition have considerable impacts on soil microbial communities in terrestrial ecosystems, ultimately influencing the carbon (C) cycling. However, the specific effects of the interactions between increased precipitation and N deposition on C:N:P stoichiometry in soil microbial biomass remain unclear. A long-term (9 yr) manipulated experiment was conducted to investigate the responses of soil microbial biomass C:N:P stoichiometry to increased precipitation and N deposition of the Desert shrubland in Gurbantunggut, northwest China. The results demonstrated that increased precipitation elevated C, N, and C:N ratios of microbial biomass by 26.9%, 18.7%, and 6.8% relative to ambient precipitation, respectively. In comparison to ambient N deposition, N addition resulted in a 37.5% increase in soil microbial biomass N and a 6.8% increase in the N:P ratio. Particularly, the interactive effects between increased precipitation and N deposition on microbial biomass P and N:P ratio were significant. Moreover, the influences of increased precipitation and N addition on microbial biomass C:N:P stoichiometry primarily occurred through changes in dissolved organic carbon content and extracellular enzyme activities. The findings underscore the crucial role of increased precipitation as a stronger driving force for variations in microbial biomass C:N:P stoichiometry in arid ecosystems, compared to N deposition.

Effects of biochar on soil microbial communities: A meta-analysis

Changes in soil microbial communities may impact soil fertility and stability because microbial communities are key to soil functioning by supporting soil ecological quality and agricultural production. The effects of soil amendment with biochar on soil microbial communities are widely documented but studies highlighted a high degree of variability in their responses following biochar application. The multiple conditions under which they were conducted (experimental designs, application rates, soil types, biochar properties) make it difficult to identify general trends. This supports the need to better determine the conditions of biochar production and application that promote soil microbial communities. In this context, we performed the first ever meta-analysis of the biochar effects on soil microbial biomass and diversity (prokaryotes and fungi) based on high-throughput sequencing data. The majority of the 181 selected publications were conducted in China and evaluated the short-term impact (<3 months) of biochar. We demonstrated that a large panel of variables corresponding to biochar properties, soil characteristics, farming practices or experimental conditions, can affect the effects of biochar on soil microbial characteristics. Using a variance partitioning approach, we showed that responses of soil microbial biomass and prokaryotic diversity were highly dependent on biochar properties. They were influenced by pyrolysis temperature, biochar pH, application rate and feedstock type, as wood-derived biochars have particular physico-chemical properties (high C:N ratio, low nutrient content, large pores size) compared to non-wood-derived biochars. Fungal community data was more heterogenous and scarcer than prokaryote data (30 publications). Fungal diversity indices were rather dependent on soil properties: they were higher in medium-textured soils, with low pH but high soil organic carbon. Altogether, this meta-analysis illustrates the need for long-term field studies in European agricultural context for documenting responses of soil microbial communities to biochar application under diverse conditions combining biochar types, soil properties and conditions of use.

Differences in Characteristics of Sample Sites Explain Variable Responses of Soil Microbial Biomass to Nitrogen Addition: A Meta-Analysis

Differences in Characteristics of Sample Sites Explain Variable Responses of Soil Microbial Biomass to Nitrogen Addition: A Meta-Analysis

Response of soil microbial biomass and enzyme activity in coffee-based agroforestry systems in a high-altitude tropical climate region of Brazil

Soil microbial communities are key indicators of changes in soil quality caused by cropping systems. Although there are studies that prove that coffee agroforestry systems increase or maintain soil organic matter levels, the effect of microbial biomass and enzymatic activity in tropical regions, especially in places with high altitude and mild temperatures, is still poorly understood. Thus, the present study aimed to evaluate the influence of two agroforestry systems (AFS-G: coffee intercropped with Grevillea robusta, AFS-C: coffee intercropped with Toona ciliata) and Coffea arabica monoculture on soil microbial biomass and activity and on the arylsulfatase and β-glucosidase enzyme activities, taking a native forest (Semi-deciduous tropical forest, with a predominance of the genera Parapiptadenia and Anadenanthera) as the control system. This study was performed in Oxisol soil areas located in the municipality of Barra do Choça, Bahia, Brazil. Litter (L, F and H layers) and soil topsoil (0–10 cm depth) samples were collected. Both were collected with four repetitions (four composite samples) in each system, litter with a 0.0625 m2 template and soil using a Dutch auger. The carbon microbial biomass, microbial activity (CO₂ released), arylsulfatase and β-glucosidase enzyme activities, organic carbon (SOC) and total nitrogen were also analyzed in the soil samples. The coffee with Grevillea robusta agroforestry system (AFS-G) did not reduce SOC compared to native forest, but the coffee with cedar agroforestry system had SOC losses at a rate of 0.56 Mg ha−1 year−1. The AFS-C cultivation system presented more MB-C (468.43 µg g−1) when compared to the other coffee systems. The AFS-G maintained the microbial activity levels and β-glucosidase and arylsulfatase enzyme activities in relation to the native forest. Coffee agroforestry systems (both AFS-G and AFS-C) in a tropical high-altitude climate region in Brazil are more favorable to maintain microorganisms and their activity in the soil, and therefore should be encouraged in order to more sustainably manage coffee growing.

Influences of rock fragment content and vegetation on soil microbial communities

Soil microbial communities are key drivers of ecosystem processes and can be strongly affected by soil properties. While the effects of soil texture and aggregate have been well studied, the effect of rock fragment content (RFC) on soil microbial communities is still poorly understood, particularly in arid ecosystem. We examined the responses of soil microbial biomass and communities to RFC gradients using a randomized block experiment with four RFCs (0 %, 25 %, 50 % and 75 %, V/V) and four planting treatments (Artemisia vestita, Bauhinia brachycarpa, Sophora davidii and no plants) in Minjiang arid valley. We explored soil community composition identified by total phospholipid fatty acids, and edaphic properties after two growth seasons. In most of current planting treatments, total phospholipid fatty acids, bacteria, saprotrophic fungi and arbuscular mycorrhizal fungi significantly decreased under 50–75 % RFCs versus 0–25 % RFCs. Compared to non-planted treatment, plants prominently increased soil microbial biomass and altered microbial communities only in 75% RFC. The ratio of gram-positive bacteria to gram-negative bacteria remarkably reduced in 75 % RFC of non-planted treatment, while significantly decreased in soil with 0 % RFC beneath A. vestita and S. davidii. These variations in soil microbial communities could be explained by the changes in soil water content, available nitrogen, total phosphorus and plant biomass allocation to fine root. These results indicated that both moderate and high RFC conditions inhibited soil microbial development, while plant can promote microbial biomass in high RFC by improving edaphic physiochemical properties and alleviating environmental stresses. Moreover, soil water content and nutrient levels explained much of the variation in soil microbial communities in these stony soils.

Contrasting responses of soil microbial biomass and extracellular enzyme activity along an elevation gradient on the eastern Qinghai-Tibetan Plateau.

Soil microbial community composition and extracellular enzyme activity are two main drivers of biogeochemical cycling. Knowledge about their elevational patterns is of great importance for predicting ecosystem functioning in response to climate change. Nevertheless, there is no consensus on how soil microbial community composition and extracellular enzyme activity vary with elevation, and little is known about their elevational variations on the eastern Qinghai-Tibetan Plateau, a region sensitive to global change. We therefore investigated the soil microbial community composition using phospholipid fatty acids (PLFAs) analysis, and enzyme activities at 2,820 m (coniferous and broadleaved mixed forest), 3,160 m (dark coniferous forest), 3,420 m (alpine dwarf forest), and 4,280 m (alpine shrubland) above sea level. Our results showed that soil microbial community composition and extracellular enzyme activities changed significantly along the elevational gradient. Biomass of total microbes, bacteria, and arbuscular mycorrhizal fungi at the highest elevation were the significantly lowest among the four elevations. In contrast, extracellular enzyme activities involved in carbon (C)-, nitrogen (N)-, and phosphorus (P)- acquiring exhibited the maximum values at the highest elevation. Total nutrients and available nutrients, especially P availability jointly explained the elevational pattern of soil microbial community, while the elevational variation of extracellular enzyme activities was dependent on total nutrients. Microbial metabolism was mainly C- and P-limited with an increasing C limitation but a decreasing P limitation along the elevational gradient, which was related significantly to mean annual temperature and total P. These results indicated a vital role of soil P in driving the elevational patterns of soil microbial community and metabolism. Overall, the study highlighted the contrasting responses of soil microbial biomass and extracellular enzyme activities to elevation, possibly suggesting the differences in adaption strategy between population growth and resource acquisition responding to elevation. The results provide essential information for understanding and predicting the response of belowground community and function to climate change on the eastern Qinghai-Tibetan Plateau.

A meta-analysis on the responses of soil microbial biomass and community structure to antibiotics

The overuse of antibiotics over the last few decades is of serious concern worldwide, and may lead to profound alterations in the biomass and structure of soil microbial communities, thus posing threats to soil ecosystems. However, on a global scale, the effects of antibiotics on soil microbial biomass and community structure remain elusive. Here, by performing 66 paired observations, we conducted one of the first global meta-analysis to evaluate the effects of various antibiotics on soil microbial communities and to explore the underlying mechanisms. Our results showed that antibiotics suppressed soil microbial biomass (indicated by PLFA) by 17 %, bacterial biomass by 17 %, and fungal biomass by 10 %. The ratio of bacteria to fungi biomass was decreased for all antibiotic types. The negative effects of antibiotics on soil microbial community and bacteria biomass attenuated with time. Additionally, the response of bacteria biomass to antibiotics, which is regulated by mean annual temperature and precipitation through soil pH and soil total nitrogen, diminished with latitude. Collectively, this study illustrates the global patterns and drivers of antibiotic-induced negative influences on microbial communities in soils, and can help identify global hotspots facing the negative effects of increasing anthropogenic usage of antibiotics.

Fifty-year habitat subdivision enhances soil microbial biomass and diversity across subtropical land-bridge islands.

Although habitat loss and subdivision are considered main causes of sharp declines in biodiversity, there is still great uncertainty concerning the response of soil microbial biomass, diversity, and assemblage to habitat subdivision at the regional scale. Here, we selected 61 subtropical land-bridge islands (with small, medium, and large land areas) with a 50-year history of habitat subdivision and 9 adjacent mainland sites to investigate how habitat subdivision-induced unequal-sized patches and isolation affects biomass, diversity, and assemblages of soil bacteria and fungi. We found that the soil bacterial and fungal biomass on all unequal-sized islands were higher than that on mainland, while soil bacterial and fungal richness on the medium-sized islands were higher than that on mainland and other-sized islands. The habitat subdivision-induced increases in microbial biomass or richness were mainly associated with the changes in subdivision-specified habitat heterogeneities, especial for soil pH and soil moisture. Habitat subdivision reduced soil bacterial dissimilarity on medium-sized islands but did not affect soil fungal dissimilarity on islands of any size. The habitat fragment-induced changes in soil microbial dissimilarity were mainly associated with microbial richness. In summary, our results based on the responses of soil microbial communities from subtropical land-bridge islands are not consistent with the island biogeographical hypotheses but are to some extent consistent with the tradeoff between competition and dispersal. These findings indicate that the response of soil microbial communities to habitat subdivision differed by degree of subdivision and strongly related to habitat heterogeneity, and the distribution of microbial diversity among islands is also affected by tradeoff between competition and dispersal.

The global positive effect of phosphorus addition on soil microbial biomass

Soil microorganisms play key roles in maintaining terrestrial biodiversity and ecosystem processes. While phosphorus (P) input into soils has been elevated due to anthropogenic activities in the past decades, how soil microorganisms respond to P addition remains unclear with diverse experimental results. By conducting a global meta-analysis with paired observations of soil microbial attributes from 119 studies, we showed that P addition globally increased microbial biomass by 7.3%. Fungal biomass and microbial P also significantly increased while microbial C:P and N:P ratios decreased with P addition. We highlighted the enhanced plant belowground biomass by P addition as a key mechanism for the positive response of soil microbial biomass. The P addition effect on microbial biomass was consistent among different ecosystem types and climates while being more positive in P-limiting soils. Our results underline that P addition may be an important approach for improving soil microbes and associated functions.

Cow bone-derived biochar enhances microbial biomass and alters bacterial community composition and diversity in a smelter contaminated soil

Bone waste could be utilized as a potential amendment for remediation of smelter-contaminated soils. Nevertheless, the influences of cow bone-derived biochar (CB) on soil microbial biomass and microbial community composition in multi-metal contaminated mining soils are still not clearly documented. Hence, the cow bone was used as feedstock material for biochar preparation and pyrolyzed at two temperatures such as 500 °C (CB500) and 800 °C (CB800), and added to a smelter soil at the dosage of 0 (unamended control), 2.5, 5, and 10% (w/w); then, the soil treatments were cultivated by maize. The CB effect on soil biochemical attributes and response of soil microbial biomass, bacterial communities, and diversity indices were examined after harvesting maize. Addition of CB enhanced total nutrient contents (i.e., total nitrogen up to 26% and total phosphorus P up to 27%) and the nutrients availability (i.e., NH4 up to 50%; NO3 up to 31%; Olsen P up to 48%; extractable K up to 18%; dissolved organic carbon up to 74%) in the treated soil, as compared to the control. The CB500 application revealed higher microbial biomass C (up to 66%), P (up to 41%), and bacterial gene abundance (up to 76%) than the control. However, comparatively a lower microbial biomass nitrogen and diversity indices were observed in the biochar (both with CB500 and CB800) treated soils than in the unamended soils. At the phylum level, the highest dose (10% of CB500 and CB800 resulted in contrasting effects on the Proteobacteria diversity. The CB50010 favored the Pseudomonas abundance (up to 793%), Saccharibacteria (583%), Parcubacteria (138%), Actinobacteria (65%), and Firmicutes (48%) microbial communities, while CB80010 favored the Saccharibacteria (386%), Proteobacteria (12%) and Acidobacteria (11%), as compared to the control. These results imply that CB500 and CB800 have a remarkable impact on microbial biomass and bacterial diversity in smelter contaminated soils. Particularly, CB500 was found to be suitable for enhancing microbial biomass, bacterial growth of specific phylum, and diversity, which can be useful for bioremediation of mining soils.

Global patterns and controls of the soil microbial biomass response to elevated CO2

Elevated CO2 concentrations (eCO2) have been widely observed to stimulate microbial growth. However, the effect of eCO2 on soil microbial biomass may depend on several factors and their interactions, such as the increase in atmospheric CO2 levels, experimental duration and mean annual precipitation (MAP). We conducted a global meta-analysis from 62 studies that included the responses of soil microbial biomass to eCO2. We found a significant positive eCO2 effect on the bacterial biomass (+9.1 %), fungi (+11 %), arbuscular mycorrhizal fungi (AMF) (+10.2 %) and actinomycetes (ACT) (+16.4 %). The positive effects were mainly observed in studies with low eCO2 levels (≤200 ppm) rather than high levels of eCO2 (>200 ppm), which could be attributable to soil N limitation. It was also found that eCO2 had a significant positive effect on soil microbial biomass in the short term (≤3 y) and under a high MAP (>800 mm). Importantly, we revealed interactive effects between the eCO2 levels, experimental duration on soil microbial biomass. With an increase in eCO2, the total microbial biomass (TMB), bacterial biomass and fungal biomass decreased over the long term (>3 y). These findings indicate the need to incorporate interactions between eCO2 and environmental factors into ecosystem models, to predict future global climate change effects more accurately and their impact on ecosystem functions.

Responses of soil microbial biomass and carbon source utilization to simulated nitrogen deposition and drought in a Cunninghamia lanceolata plantation

Chinese fir (Cunninghamia lanceolata) plantation is a dominant forest type and carbon sink in the subtropical region in China. An experiment with simulated nitrogen deposition (addition of 40 kg N·hm-2·a-1) and drought (50% of precipitation exclusion, PE) was established in Chinese fir plantation in 2018. Soil samples (0-15 cm) were collected in summer (July 2020) and winter (January 2021). Soil microbial biomass, colony forming units (CFUs) and carbon source utilization were determined through phospholipid fatty acids (PLFAs), plate count, and Biolog methods, respectively. The results showed significant seasonal variations of PLFAs-related microbial biomass and composition. Soil bacterial and fungal CFUs tended to be decreased by nitrogen addition or precipitation exclusion treatment, and bacterial CFUs were more sensitive to the two treatments than fungal CFUs. Soil microbial function (i.e. carbon source utilization) was not affected by nitrogen addition, but significantly decreased by precipitation exclusion. There was a significant positive correlation between bacterial CFUs and microbial function, indicating the crucial roles of culturable bacteria in microbial carbon transformation. Our results highlight the critical effects of nitrogen deposition and 50% reduced precipitation on microbes in topsoil of fir plantation, with implications for unraveling soil microbial ecological function of subtropical forest ecosystem under global changes in future.

Response of soil microbial biomass C, N, and P and microbial quotient to agriculture and agricultural abandonment in a meadow steppe of northeast China

The carbon and nutrients in the soil microbial biomass (SMB) and their proportion in soil elements, namely soil microbial quotient (SMQ), are the key indicators of the soil quality and quickly respond to the shift in the land-use pattern. However, the degree of the land-use shift influences on the soil microbial biomass, and the soil microbial quotient in the meadow steppe is not well-understood. The soil microbial biomass carbon (MBC), nitrogen (MBN), phosphorous (MBP), and SMQ were determined separately in grassland, cropland, and abandoned cropland in four sites within 50 km at a meadow steppe in northeast China. The results showed that the soil MBC, MBN, and MBP declined significantly as soil depth increased among the three land-use patterns. Agriculture has resulted in a significant decrease in the soil MBC, MBN, MBP, and SMQ compared to their corresponding values in grassland. The soil MBC content significantly was increased at the 0–10 cm soil layer after agriculture abandonment, but the SMQ had no significant improvement in the entire profile when compared to cropland. Besides, for the three types of land-use patterns, the C, N, and P stoichiometry of the soil microbial biomass was relatively stable, except for the stoichiometry in the relatively deep soil layer. Overall, the present agricultural abandonment (~ 19 years) got a certain of restoration in soil microbial biomass. Their corresponding values, however, were significantly lower than those found in native grassland. This highlighted that the restoration of the poor soil quality caused by the long term agriculture cultivation is a slow and hard process; it is important to maintain natural grasslands for protecting and maintaining soil microbial biomass and SMQ in the meadow steppe of northeast China.

High grazing intensity suppress soil microorganisms in grasslands in China: A meta-analysis

Livestock grazing, the main type of management activity in grasslands drives the structure and function of these ecosystems. However, the responses of soil microbial biomass and community composition to grazing remain poorly understood, compared with plants, nutrients and soil properties. We conducted a meta-analysis of independent grazing intensity (low grazing intensity, intermediate grazing intensity and high grazing intensity) experiments, including 69 studies with 934 paired observations, in steppe ecosystems of China and evaluated their effects on soil microbial biomass and community composition. Our results revealed that high grazing intensity consistently reduces total microbial biomass, the biomass of bacteria, fungi, actinomycetes, gram-positive bacteria and gram-negative bacteria by 33%, 31%, 53%, 14%, 19% and 36%, respectively, whereas low grazing intensity has limited effect on these microbial variables. High grazing intensity strongly reduced the numbers of bacteria, fungi and actinomycetes by 92%, 65%, 30%, respectively, but low grazing intensity had limited effects on them. The responses of fungal numbers to grazing intensity were positively correlated with those of plant aboveground biomass. Meanwhile, the response of bacterial numbers was positively correlated to that of soil bulk density. Our findings indicate that aboveground plant biomass and soil bulk density might be the underlying drivers that change the numbers of fungi and bacteria to grazing intensities in China. Our findings highlight the negative effect of high grazing intensity on soil microbial biomass and numbers in natural grasslands.

Greater soil microbial biomass loss at low frequency of N addition in an Inner Mongolia grassland

Abstract Soil microbial biomass is critical for biogeochemical cycling and serves as precursor for carbon (C) sequestration. The anthropogenic nitrogen (N) input has profoundly changed the pool of soil microbial biomass. However, traditional N deposition simulation experiments have been exclusively conducted through infrequent N addition, which may have caused biased effects on soil microbial biomass compared with those under the natural and continuous N deposition. Convincing data are still scarce about how the different N addition frequencies affect soil microbial biomass. By independently manipulating the frequencies (2 times vs. 12 times N addition yr–1) and the rates (0–50 g N m−2 yr−1) of N addition, our study aimed to examine the response of soil microbial biomass C (MBC) to different N addition frequencies with increasing N addition rates. Soil MBC gradually decreased with increasing N addition rates under both N addition frequencies, while the soil MBC decreased more at low frequency of N addition, suggesting that traditional studies have possibly overestimated the effects of N deposition on soil microbial biomass. The greater soil microbial biomass loss with low N frequency resulted from the intensified soil acidification, higher soil inorganic N, stronger soil C and N imbalance, less net primary production allocated to belowground and lower fungi to bacteria ratio. To reliably predict the effects of atmospheric N deposition on soil microbial functioning and C cycling of grassland ecosystems in future studies, it is necessary to employ both the dosage and the frequency of N addition.

A Meta-Analysis on the Responses of Soil Microbial Biomass and Community Structure to Antibiotics

A Meta-Analysis on the Responses of Soil Microbial Biomass and Community Structure to Antibiotics