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.
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•Land use changes (LUCs) involve manipulation of forests to farmlands.•Organic matter decrease due to LUCs reduces soil microbial biomass levels.•Higher soil organic matter supports greater soil microbial biomass in forest.•Reforestation may restore beneficial soil microbial communities and biomass.
•The global maps of soil microbial biomass C, N, and P were generated.•The storage of soil microbial biomass C, N, and P for major biomes and globally were estimated.•Soil organic carbon predicts ...soil microbial biomass C, N, and P at a global scale.
Soil microbes play key roles in driving and regulating nutrient cycling in terrestrial ecosystems. However, a lack of global-scale information regarding the distribution of soil microbial biomass carbon (SMB C), nitrogen (SMB N), and phosphorus (SMB P) in terrestrial ecosystems has limited our ability to incorporate the broad-scale soil microbial nutritional properties and the associated processes into biogeochemical models. Here, we synthesized a global dataset including 3801 observations for SMB C, 3154 observations of SMB N, and 2429 observations of SMB P in the top 0–30 cm soil depth. Based on this comprehensive global dataset, we generated quantitative and spatially explicit maps of SMB C, N, and P across terrestrial ecosystems using a random forest approach. We also quantified the relative importance of multiple environmental variables in predicting the spatial variation of SMB C, N, and P concentrations and then made further predictions at a global scale. Soil organic carbon (SOC) was the most important factor in predicting SMB C, N, and P at a global scale. At the global scale, the storage of SMB C, N, and P were estimated to be 23.13 Pg C, 3.93 Pg N and 2.16 Pg P in the top 0–30 cm soil surface, respectively. Our global maps of SMB C, N, and P presented here can be used to constraint Earth system models, and provide the first step forward to predict the roles of soil microbial nutrients in terrestrial nutrient cycling.
•We predicted the global pattern of soil microbial quotients and their drivers.•Climate factor regulated ratio of microbial biomass carbon to soil organic carbon.•Ratio of microbial biomass carbon to ...soil organic carbon decreased with latitude.•Soil microbial quotient showed obvious seasonal variations.
The microbial quotient of soil, defined as the proportion of soil elements present in soil microorganisms, reflects the capacity of microbial communities to regulate processes like organic matter decomposition and nutrient cycling. These processes are vital for ecosystem functioning, supporting plant growth, and maintaining soil fertility. However, the global scale’s magnitude and drivers of soil microbial quotients remain elusive. This study complied a comprehensive dataset comprising ratios of microbial biomass carbon to soil organic carbon (MBC/SOC), microbial biomass nitrogen to total nitrogen (MBN/TN), and microbial biomass phosphorus to total phosphorus (MBP/TP) from 1394 published studies until 2022 to investigate global patterns of soil microbial quotients using a random forest model. The data showed that the modeled global means for MBC/SOC, MBN/TN, and MBP/TP at 0–30 cm soil depth were 2.2 %, 3.5 %, and 7.0 %, respectively. Climatic factors, including relative humidity, mean annual temperature (MAT), and mean annual precipitation (MAP), were identified as the most important drivers of MBC/SOC at the global scale. Modeled MBC/SOC showed higher values in tropical/subtropical biomes than in temperate and boreal biomes. Conversely, MBN/TN and MBP/TP were higher in boreal forests and tundra than in tropical/subtropical biomes, possibly reflecting nitrogen and phosphorus limitations as well as nutrient recycling in microbial biomass in cold regions. In addition, MBC/SOC displayed obvious seasonal variations, with the highest values in spring (2.4) and the lowest in winter (1.9). This variation is likely a result of the higher temperature sensitivity of soil microbial biomass compared to soil organic carbon. Overall, the findings of this study significantly enhance our understanding of the mechanisms driving soil organic matter and nutrient cycling across terrestrial ecosystems. It also supplies critical parameters that could improve the modeling of soil nutrient cycling.
Continuous rice-wheat (RW) rotation with conventional agronomic practices has resulted in declining factor productivity and degrading soil resources. A farmer's participatory research trial was ...conducted in Karnal, India to evaluate 8 combinations of cropping systems, tillage, crop establishment method and residue management effects on key soil physico-chemical and biological properties. Treatments (T) 1–4 involved RW and 5–8 maize-wheat (MW) with conventional tillage (CT) and zero tillage (ZT) with (+R) and without (−R) residue recycling. Residue was either incorporated (Ri) or mulched (Rm). Treatment 1 (RW/CT−R) had the highest bulk density (BD) (1.47Mgm−3) and T8 (MW/ZT+Rm), the lowest (1.34Mgm−3). After 3years of cropping, soil accumulated more organic C in (a) MW (9.33Mgha−1) than RW (8.5Mgha−1), (b) ZT (9.25Mgha−1) than CT (8.58Mgha−1), and (c)+R (10.18Mgha−1) than –R (7.65Mgha−1). MW system with ZT and residue (T8: MW/ZT+Rm) registered 208, 263, 210 and 48% improvement in soil microbial biomass C (MBC) and N, dehydrogenase activity (DHA) and alkaline phosphatase activity (APA), whereas RW system in T4 (RW/ZT+Rm) registered 83, 81, 44 and 13%, respectively as compared with T1 (RW/CT−R), the business as usual scenario. Treatment 8 (MW/ZT+Rm) recorded the highest microbial population viz. bacteria, fungi and actinomycetes. The most abundant micro-arthropods present in the soil of experimental plot were Collembola, Acari and Protura which varied with treatments. Soil MBC, APA, BD and micro-arthropod population were identified as the key indicators and contributed significantly towards soil quality index (SQI). MW system with ZT and Rm (T8) recorded the highest SQI (1.45) followed by T6 (1.34) and the lowest score (0.29) being in T1 (RW/CT−R). The SQI was higher by 90% in MW compared to RW, 22% in ZT compared to CT, and 100% in residue recycling compared with residue removal. System yield was strongly related to key soil quality indicators and also positively correlated with SQI. Longer-term studies are essential to realize maximal effects of improvements in soil health on crop yields.
•Cropping system, tillage, crop establishment and residue had direct influence on soil biological quality•Soil enzyme activities were significantly increased in conservation agriculture based maize-wheat system•Soil MBC, alkaline phosphatase activity, bulk density & micro-arthropod population identified as key soil quality indicators•Soil quality index was higher in maize-wheat system•Residue recycling compared to residue removal and ZT than CT registered higher soil quality index.
Soil microbial biomass and microbial stoichiometric ratios are important for understanding carbon and nutrient cycling in terrestrial ecosystems. Here, we compiled data from 12245 observations of ...soil microbial biomass from 1626 published studies to map global patterns of microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP), and their stoichiometry using a random forest model. Concentrations of MBC, MBN, and MBP were most closely linked to soil organic carbon, while climatic factors were most important for stoichiometry in microbial biomass ratios. Modeled seasonal MBC concentrations peaked in summer in tundra and in boreal forests, but in autumn in subtropical and in tropical biomes. The global mean MBC/MBN, MBC/MBP, and MBN/MBP ratios were estimated to be 10, 48, and 6.7, respectively, at 0–30 cm soil depth. The highest concentrations, stocks, and microbial C/N/P ratios were found at high latitudes in tundra and boreal forests, probably due to the higher soil organic matter content, greater fungal abundance, and lower nutrient availability in colder than in warmer biomes. At 30–100 cm soil depth, concentrations of MBC, MBN, and MBP were highest in temperate forests. The MBC/MBP ratio showed greater flexibility at the global scale than did the MBC/MBN ratio, possibly reflecting physiological adaptations and microbial community shifts with latitude. The results of this study are important for understanding C, N, and P cycling at the global scale, as well as for developing soil C‐cycling models including soil microbial C, N, and P as important parameters.
We provided a three‐dimensional mapping of soil microbial biomass C, N, and P concentrations at the global scale. Modeled seasonal MBC concentration peaked in summer in tundra and boreal forests, but in autumn in subtropical and tropical biomes. The concentration of MBC decreased with soil depth and this decrease was more pronounced at higher than at lower latitudes.
Soil microbes play important roles in regulating terrestrial carbon and nitrogen cycling and strongly influence feedbacks of ecosystems to global warming. However, the inconsistent responses of ...microbial biomass carbon (MBC) and nitrogen (MBN) to experimental warming have been observed, and the response ratio between MBC and MBN (MBC:MBN) has not been identified. This meta-analysis synthesized warming experiments at 58 sites globally to investigate the responses of MBC:MBN to climate warming. Our results showed that warming significantly increased MBC by 3.61 ± 0.80% and MBN by 5.85 ± 0.90% and thus decreased the MBC:MBN by 3.34 ± 0.66%. MBC showed positive responses to warming but MBN exhibited negative responses to warming at low warming magnitude (<1 °C); however, at high warming magnitude (>2 °C) the results were inverted. The different effects of warming magnitude on microbial biomass resulted from the warming-induced decline in soil moisture and substrate supply. Moreover, MBC and MBN had strong positive responses to warming at the mid-term (3–4 years) or short-term (1–2 years) duration, but the responses tended to decrease at long-term (≥5 years) warming duration. This study fills the knowledge gap on the responses of MBC:MBN to warming and may benefit the development of coupled carbon and nitrogen models.
•Warming significantly increased MBC and MBN, but decreased their ratio.•The responses of MBC and MBN decrease with warming duration.•Ecosystem model need integrate microbial responses to warming.
The global geographic distribution of subseafloor sedimentary microbes and the cause(s) of that distribution are largely unexplored. Here, we show that total microbial cell abundance in subseafloor ...sediment varies between sites by ca. five orders of magnitude. This variation is strongly correlated with mean sedimentation rate and distance from land. Based on these correlations, we estimate global subseafloor sedimentary microbial abundance to be 2.9⋅10 ²⁹ cells corresponding to 4.1 petagram (Pg) C and ∼0.6% of Earth’s total living biomass. This estimate of subseafloor sedimentary microbial abundance is roughly equal to previous estimates of total microbial abundance in seawater and total microbial abundance in soil. It is much lower than previous estimates of subseafloor sedimentary microbial abundance. In consequence, we estimate Earth’s total number of microbes and total living biomass to be, respectively, 50–78% and 10–45% lower than previous estimates.
Most studies on the effects of biochar and fertilizer on soil carbon (C) and nitrogen (N) mineralization, and microbial C and N content, are restricted to a single soil type, limiting our ...understanding of the interactions between these factors and microbial functions. To address this paucity in knowledge, we undertook a 3-year experiment using four contrasting soils to assess the role of peanut shell biochar and fertilizer on C and N mineralization, microbial C and N, and N stoichiometry. Across all four soils, biochar significantly (P < 0.05) increased soil carbon mineralization (Cmin) and nitrogen mineralization (Nmin) over three years compared to fertilizer and the control. Biochar also increased total C (Csoil) across the four soils in year 1, with the Fluvisol recording greater total C in year 2 and Phaeozem having greater total C in year 3. Biochar resulted in a higher microbial biomass C (Cmic), total N (Nsoil) and microbial biomass N (Nmic); the degree of change was closely related to Csoil and Nsoil. There was a positive correlation between Cmic:Nmic and Csoil:Nsoil; while Csoil and Cmic increased following amendment with biochar, which reduced the soil C and N stoichiometric imbalance (Nimb) caused by the increase in the C to N ratio. However, fertilizer exacerbated the imbalance of soil C and N stoichiometry. Fertilizer also reduced the Csoil:Nsoil and Cmic:Nmic ratios. Soil pH had a positive correlation with Csoil, Cmic, Nmic, Cmin, Nmin, Csoil:Nsoil, Cmic:Nmic, and biochar increases this correlation. The soil pH was negatively correlated with Cimb:Nimb and Nsoil. Fertilizer was positively correlated Cimb:Nimb and Nsoil. In contrast, fertilizer N application lowered microbial biomass C:N. We conclude that biochar reduces the imbalance of soil C and N stoichiometry, whereas fertilizer increased this imbalance. Biochar had a greater impact on C and N in soils with a lower pH.
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•Biochar reduces the imbalance of soil C and N stoichiometry.•Fertilizers exacerbate the imbalance of soil C and N stoichiometry.•Biochar is conducive to the sustainable development of agriculture.•Biochar improves soil MBC content and C and N mineralization rate.•Changes of C and N indexes in different soils are closely related to soil pH.
Anthropogenic nitrogen (N) deposition is expected to increase substantially and continuously in the future. Soil N availability regulates microbial communities and the decomposition and formation of ...soil organic matter, which have great impacts on global carbon (C) cycling. We conducted a meta-analysis based on 454 N-addition experiments in order to synthesize the patterns and mechanisms of responses by soil microbial communities to N addition in various biomes (i.e., boreal forest, temperate forest, tropical/subtropical forest, grassland, and desert). Results showed that the effects of N addition on the total microbial biomass varied depending on biome types, methodologies (fumigation–extraction technique vs. total phospholipid fatty acid), and N-addition rates. Nitrogen addition consistently decreased the microbial C:N and fungi to bacteria ratio (F:B), but increased Gram positive bacteria to Gram negative bacteria ratio (GP:GN) among biome types and N-addition rates. Nitrogen addition increased soil N availability and thereby resulted in soil acidification. Regression technique and principal component analyses showed that the shifts in the F:B and GP:GN mainly resulted from enhanced N availability due to N addition rather than soil acidification. When the N addition rate is lower than 100 kg N ha−1 year−1, about ten times higher than of global normal rate, the positive response of microbial growth was found. Overall, these findings revised the previous notion that N addition inhibited the microbial growth. Microbial species shifts might accentuate or mitigate the effects of alterations in microbial biomass at the ecosystem level, highlighting the critical role of microbial community composition in soil ecosystem functions under N deposition scenarios.
•A meta-analysis based on 454 N addition experiments.•Current normal rates of N deposition may not inhibit microbial growth.•N addition decreased fungi to bacteria ratio.•N addition increased Gram positive bacteria to Gram negative bacteria ratio.•N addition affects microbes through resources enhancement rather than acidification.
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