Soil Microbial Biomass Research Articles

Precipitation patterns impact soil aggregates and organic carbon of an alpine wetland on the Qinghai-Tibetan Plateau

Global climate change is predicted to influence both precipitation amount and frequency in many regions. However, little is known about how precipitation changes affect soil aggregates and soil organic carbon (SOC) in alpine wetlands. Plots of an alpine wetland on the Qinghai-Tibetan Plateau were subjected to two precipitation frequencies (high vs. low, i.e., 1 and 3 times of nature rainfall intervals) crossed with two precipitation amounts (high vs. low, i.e., 100 % and 70 % of the amount of natural rainfall). Two years later, we investigated changes of soil aggregates (silt + clay, < 53 μm; microaggregates, 53∼250 μm; and macroaggregates, >250 μm) and SOC in three soil depths, i.e., 0–15 cm, 15–30 cm and 30–50 cm. Averaged across the three soil depths, the content of SOC and dissolved organic carbon (DOC) in the simulated natural precipitation (high amount, high frequency treatment) were 127.22 g kg−1 and 0.19 g kg−1, respectively. Reducing precipitation amount or frequency led to a 19.6 %-26.2 % increase in SOC, and 28.7 %-44.4 % increase in DOC. Microbial biomass carbon in natural precipitation was 1.33 g kg−1 across the three soil depths, and its response to precipitation varied with soil depths. The fraction of macroaggregates in the 0–15 cm soil depth was 63.5 % in the simulated natural precipitation treatment, and decreased by 18.6 %–21.9 % in response to reduced precipitation amount or frequency. Aggregate fractions in the 15–30 cm soil depth did not respond significantly to the changes of precipitation patterns. Reducing precipitation frequency or amount decreased the contribution of macroaggregate-associated organic carbon to SOC compared to the simulated natural precipitation, but increased the contribution of microaggregate-associated organic carbon, especially in the 0–15 cm soil depth. Structural equation models revealed that SOC was regulated by soil aggregate composition and microbial biomass carbon. The buffering of the surface soil weakened the effects of precipitation changes on aggregates and aggregate-associated organic carbon in the deep soil. These results suggest that reducing precipitation frequency or amount can decrease the fraction of macroaggregates in the surface soil, and weaken the physical protection of macroaggregates for SOC. Thus, changes in precipitation patterns may have a significant impact on SOC storage and stability in alpine wetlands through their influence on soil aggregate composition.

Organic substitution regime with optimized irrigation improves potato water and nitrogen use efficiency by regulating soil chemical properties rather than microflora structure

Context or problemImproving water and fertilizer use efficiency is an inevitable choice for sustainable potato production in North China. However, the regulation mechanism of potato water and nitrogen use efficiency under water-nitrogen coupling (W-N) regime is still unknown. Objective or research questionThe objectives from a 3-year field experiment were (1) to assess the impact of W-N regimes on potato yield and water and nitrogen use efficiency, (2) to elucidate the soil microflora structure under W-N regimes, and (3) to determine the relationship between soil chemical properties, microflora structure, and potato water and nitrogen use efficiency. MethodsA three-year two-factor split-zone potato field experiment was conducted in arid and semi-arid regions of the Inner Mongolian Plateau, with irrigation [(rainfed (W0), optimized (soil-based) irrigation (W1), conventional irrigation (W2)] as the primary treatment and N fertilizer [no N (N0), chemical N (N1), 25 % manure substitution (N2)] as the secondary treatment. ResultsPotato yield and water productivity followed N2 > N1 > N0, and partial nitrogen productivity and nitrogen agronomic efficiency followed N2 > N1 at the same irrigation level. Potato yield, nitrogen internal efficiency, partial nitrogen productivity and nitrogen agronomic efficiency first increased and then decreased, whereas water productivity gradually decreased with increasing irrigation levels under the same fertilization regime. Moreover, potato yield, soil total nitrogen, organic carbon, and microbial biomass carbon and nitrogen content peaked with the W1N2 regime. W-N regimes significantly influenced soil microbial community structure. Soil microbial α-diversity was less variable under W1 and N2 conditions. Soil bacterial network complexity and robustness were higher in W1 and W2 than in W0 regimes, whereas the opposite was true for fungi. The complexity and robustness of the soil bacterial and fungal network demonstrated for three fertilization regimes were higher in N1 and N2 than in N0 regimes. Neutral community model showed that soil microflora in W-N regime was mainly influenced by stochastic processes. PLSPM showed that organic substitution regime with optimized irrigation improves potato water and nitrogen use efficiency by regulating soil chemical properties rather than microflora structure. ConclusionsW1N2 regime synergizes well to improve potato water and N use efficiency and soil microflora stability, and organic substitution regime with optimized irrigation improves potato water and nitrogen use efficiency by regulating soil chemical properties. Implications or significanceOur findings initially clarified the regulatory mechanisms of potato water and nitrogen use efficiency in North China, offering theoretical guidance for further optimizing irrigation and fertilization management.

Long-term agricultural cultivation decreases microbial nutrient limitation in coastal saline soils

Soil enzyme activities are pivotal for diverse biochemical processes and are sensitive to land use changes. They can indicate soil microbial nutrient limitations. Nonetheless, the mechanism governing the response of soil microbial nutrient limitation to land use alterations in coastal regions remains elusive. We assessed soil nutrients, microbial biomass, and extracellular enzyme activities across various land use types—natural (wasteland and woodland) and agricultural (farmland and orchard)—in the Hangzhou Bay area, China. All four land use types experience co-limitation by carbon (C) and phosphorus (P). However, the extent of microbial resource limitations varies among them. Long-term agricultural practices diminish microbial C and P limitations in farmland and orchard soils compared to natural soils, as evidenced by lower ecoenzymatic C:N ratios and vector lengths, alongside higher microbial carbon use efficiency (CUE). Soil nutrient stoichiometric ratios and CUE are primary factors influencing microbial C and P limitations. Thus, fostering appropriate land use and management practices proves imperative to regulate soil nutrient cycles and foster the sustainable management of coastal areas.

Sheep rotational grazing strategy to improve soil organic carbon and reduce carbon dioxide emission from spring wheat in an arid region

Context Cultivating forage crops is crucial to improve feed production, and grazing is an important utilisation method to improve soil fertility. Aim Improving soil organic carbon (SOC) content and reducing carbon dioxide (CO2) emission through grazing management from a spring wheat field. Methods We compared sheep rotational grazing and control, and studied their effects on SOC and CO2 emission from a spring wheat field. Key results Sheep rotational grazing improved SOC content (by 23.5%) and soil easily oxidised organic carbon (EOC) content (by 7.7%) and reduces soil microbial biomass carbon (MBC) content (by 35.8%) compared with the control. Sheep rotational grazing reduced CO2 emission compared with the control. Sheep grazing reduced cumulative CO2 emission by 28.9% and 33.0% in May and June compared with the control. Conclusions Sheep grazing improved SOC content and reduce CO2 emission from a spring wheat field. Implications Based on our short-term study, sheep rotational grazing has a significant effect on SOC, EOC and MBC contents and CO2 emission from spring wheat fields in arid regions. For a large-scale assessment of sheep grazing on soil fertility and CO2 emission, more investigation for different soils and climates is necessary. Furthermore, a long-term study is also necessary to better understand the effect of sheep rotational grazing on soil fertility and CO2 emission from spring wheat fields in arid regions.

Response of soil microbial homeostasis to soil ecological stoichiometric balance in a World Natural Heritage area

Soil microbial biomass stoichiometry homeostasis is essential for microorganism survival and ecosystem stability. Despite its importance, research on soil microbial homeostasis in Natural World Heritage Sites (NWHS) is lacking. This study analyzed ecological stoichiometry and microbial homeostasis in surface (0–20 cm) and subsurface (20–40 cm) soils across various vegetation types in Fanjing Mountain, an NWHS in China. The objective was to explore microbial homeostasis in relation to soil ecological stoichiometry and identify key influencing factors. Results indicated that microbial biomass stoichiometry in surface soil is higher than in subsurface soil for 5 vegetation types, mirroring nutrient stoichiometry but contrasting enzyme stoichiometry. Vector length (VL) suggests higher C limitation in subsurface soil for all vegetation types, while vector angle (VA) shows P limitation in surface soil of certain types and N limitation in subsurface soil across all types. Random forest analysis revealed that the microbial carbon-nitrogen ratio (MB C/N) was mainly contributed by C/N (14.11 %), SOC (12.31 %), pH (10.52 %), NH4+-N, SWC, NO3--N in the surface soil, and NO3--N (15.74 %), altitude, SWC, SOC, C/N in the subsurface soil, whereas for the microbial carbon-phosphorus ratio (MB C/P), altitude (12.16 %), SWC (9.86 %), and AP were the main contributing factors in the surface soil, and in the subsurface soil, altitude (10.49 %), C/P, SWC, SOC, and TP. This study provides insights into ecological stoichiometry, homeostasis, and nutrient limitations in Fanjing Mountain, aiding vegetation nutrient balance management in NWHS.

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.

Grazing cover crops increases soil microbial biomass in Texas semiarid ecoregion

AbstractIntegrated crop‐livestock systems (ICLS) bring diversity to agricultural systems, enhancing soil ecosystem services, food production, and environmental sustainability. Resource utilization efficiency practices under semiarid ecoregions include dual systems that grow wheat (Triticum aestivum L.) for both grain and grazing (G) and recently complementary to wheat dual systems, cover crops (CC) for feeding both the soil and cattle during the fallow period. The latter continues to generate interest and there is a paucity of information on associated biochemical cycles. The objective was to evaluate the impact of CC and grazing thereof on soil microbiota structure, diversity, proliferation, and nutrient cycling. Introducing CC to no‐till (NT [NTC]) and grazing CC (NTCG [ICLS]), increased total PLFA biomass (TPB) for ungrazed CC (NTC) by 12%, and grazed CC (NTCG [ICLS]) by 20%; total bacteria biomass (TBB) by 10% for NTC and 24% for NTCG; total fungal biomass (TFB) by 9% for NTC and 21% for NTCG. The CC significantly increased Gram (−) bacteria biomass by 17% and 34% for NTC and NTCG, respectively; the CC significantly increased Gram (+) bacteria biomass by 6% and 12% for NTC and NTCG, respectively; and the CC significantly increased arbuscular mycorrhizal fungi by 55% and 89% for NTC and NTCG respectively, compared to NT fallow practice. Significant correlations were observed for NO3−–N, NH4+–N, water‐extractable organic nitrogen, total nitrogen, and water‐extractable organic carbon with TPB, TBB, and TFB using Haney soil health methods. Based on the measured parameters, the soil health status decreased in the order NTCG &gt; NTC &gt; NT &gt; CT, where NT is the no‐till, C is the cover crop, G is the grazing, and CT is the conventional‐till. Grazing CC enhanced soil bacterial biomass over CC in solitude.

Conversion of pure Chinese fir plantation to multi-layered mixed plantation increases organic phosphorus accumulation and transformation within soil aggregates

Evaluation of the impacts of environmental factors and microbial communities on soil organic phosphorus (Po) availability is needed to clarify P cycling and regulate plantations productivity. However, the effects on Po accumulation and transformation of converting pure Chinese fir plantation to multi-layered mixed plantation and their regulatory mechanisms remain unclear. The aim of this study was to examine the impacts of the transformation of pure stand of Chinese fir (Cunninghamia lanceolata; PP) to mixed plantation with multiple tree species (C. lanceolata, Castanopsis hystrix, and Michelia hedyosperma; MP) on Po accumulation and transformation within topsoil (0–10 cm) aggregates in subtropical China. Our results showed that the soil organic carbon (SOC), total nitrogen (TN), ammonium nitrogen (NH4+-N), and available phosphorus (AP), as well as the carbon‑nitrogen ratio of soil (C/Nsoil) and carbon‑phosphorus ratio of soil (C/Psoil) were significantly higher (P < 0.05) of all aggregates in MP than those in PP. The quantities of soil microbial biomass C, N, P (MBC, MBN, and MBP) in all different aggregates were significantly greater (P < 0.05) in MP than in PP. The phospholipid fatty acid contents related to bacteria, fungi, arbuscular mycorrhizal fungi (AMF), and actinomycetes were significantly greater in all aggregate classes (P < 0.05) in MP relative to PP. The activities of all tested C, N, and P hydrolytic enzymes, as well as labile organic P, moderately labile organic P, moderately resistant organic P, and highly resistant organic P contents, were significantly higher of most aggregate size classes in MP. Finally, redundancy analysis (RDA) suggested that Po fractions were primarily affected by the NH4+-N, litterfall biomass (LF), carbon‑nitrogen ratio of litter (C/Nlitter), SOC and fine root biomass (FR). Our findings suggest that converting pure Chinese fir plantations into multi-layered mixed plantations may represent an effective management strategy for promoting organic P accumulation and transformation by regulating soil and microbial properties in degraded soils of Chinese fir plantations.

Nano-Bioremediation of Arsenic and Its Effect on the Biological Activity and Growth of Maize Plants Grown in Highly Arsenic-Contaminated Soil.

Arsenic (As)-contaminated soil reduces soil quality and leads to soil degradation, and traditional remediation strategies are expensive or typically produce hazardous by-products that have negative impacts on ecosystems. Therefore, this investigation attempts to assess the impact of As-tolerant bacterial isolates via a bacterial Rhizobim nepotum strain (B1), a bacterial Glutamicibacter halophytocola strain (B2), and MgO-NPs (N) and their combinations on the arsenic content, biological activity, and growth characteristics of maize plants cultivated in highly As-contaminated soil (300 mg As Kg-1). The results indicated that the spectroscopic characterization of MgO-NPs contained functional groups (e.g., Mg-O, OH, and Si-O-Si) and possessed a large surface area. Under As stress, its addition boosted the growth of plants, biomass, and chlorophyll levels while decreasing As uptake. Co-inoculation of R. nepotum and G. halophytocola had the highest significant values for chlorophyll content, soil organic matter (SOM), microbial biomass (MBC), dehydrogenase activity (DHA), and total number of bacteria compared to other treatments, which played an essential role in increasing maize growth. The addition of R. nepotum and G. halophytocola alone or in combination with MgO-NPs significantly decreased As uptake and increased the biological activity and growth characteristics of maize plants cultivated in highly arsenic-contaminated soil. Considering the results of this investigation, the combination of G. halophytocola with MgO-NPs can be used as a nanobioremediation strategy for remediating severely arsenic-contaminated soil and also improving the biological activity and growth parameters of maize plants.

Fire-deposited charcoal enhances soil microbial biomass in a recently harvested subtropical plantation forest

Charcoal, a byproduct of biomass burning, is widely and heterogeneously distributed in fire-affected ecosystems. However, few field studies have been conducted to evaluate the effects of fire-deposited charcoal on the post-fire soil quality. In this study, we aimed to investigate whether charcoal generated during post timber harvest broadcast burning influenced the recovery of individual soil properties and overall soil quality in subtropical forest plantations. Broadcast burning was conducted on experimental Pinus massoniana plantation timber harvest sites in southern China. Surface soils (0–10 cm) were collected in plots established on the burnt sites five years after the disturbance event. Plots were established immediately after burning with three different levels of charcoal input (C0, removal of all visible charcoal; C1, charcoal retained in-situ; C2, charcoal removed from C0 added to C2) and an unburnt control (UB). Thirty-two soil indicators representing soil physical, chemical, and biological properties were determined. The results showed that 11 indicators exhibited significant differences among the treatments, with significantly lower SOM, microbial biomass carbon (MBC), peroxidase (POD) and leucine aminopeptidase (LAP) activities for the C0 and C1 plots than the UB plots (P < 0.05), while no significant difference was observed between the UB and C2 plot (P > 0.05). The soil available N, P and exchangeable nutrient contents were not significantly different among the treatments (P > 0.05). Our results indicate that SOM and microbial attributes did not recover five years after the disturbance event and that charcoal appeared to play a positive role in the post-fire soil restoration. Whether the accelerated recovery of soil restoration induced by charcoal might contribute to higher forest productivity needs to be testified in combination with plant growth and performance analysis in the future.

Differential carbon accumulation of microbial necromass and plant lignin by pollution of polyethylene and polylactic acid microplastics in soil

The wide microplastics (MPs) occurrence affects soil physicochemical and biological properties, thereby influencing its carbon cycling and storage. However, the regulation effect of MPs on soil organic carbon (SOC) formation and stabilization remains unclear, hindering the accurate prediction of carbon sequestration in future global changes under continuous MP pollution. Phospholipid fatty acids, amino sugars and lignin phenols were used in this study as biomarkers for microbial community composition, microbial necromass and plant lignin components, respectively, and their responses to conventional (polyethylene; PE) and biodegradable (polylactic acid; PLA) MPs were explored. Results showed PLA MPs had positive effects on soil microbial biomass, while the positive and negative effects of PE MPs on microbial biomass varied with MP concentration. PE and PLA MPs increased microbial necromass contents and their contribution to SOC, mainly due to the increase in fungal necromass. On the contrary, PE and PLA MPs reduced lignin phenols and their contribution to SOC, mainly owing to the reduction in vanillyl-type phenols. The response of microbial necromass to PLA MPs was higher than that to PE MPs, whereas the response of lignin phenols was the opposite. MPs increased SOC level, with 83%–200% and 50%–75% of additional SOC in PE and PLA treatments, respectively, originating from microbial necromass carbon. This finding indicates that the increase in SOC pool in the presence of MPs can be attributed to soil microbial necromass carbon, and MPs increased capacity and efficacy of microbial carbon pump by increasing microbial turnover and reducing microbial N limitation. Moreover, the increase in amino sugars to lignin phenols ratio in PE treatment was higher than that in PLA treatment, and the increase in SOC content in PLA treatment was higher than that in PE treatment, indicating a high possibility of SOC storage owing to PLA MPs.

Edaphic factors mediate the responses of forest soil respiration and its components to nitrogen deposition along an urban-rural gradient

Exploring the influences of nitrogen deposition on soil carbon (C) flux is necessary for predicting C cycling processes; however, few studies have investigated the effects of nitrogen deposition on soil respiration (Rs), autotrophic respiration (Ra) and heterotrophic respiration (Rh) across urban-rural forests. In this study, a 4-year simulated nitrogen deposition experiment was conducted by treating the experimental plots with 0, 50, or 100 kg·ha−1·year−1 of nitrogen to check out the mechanisms of nitrogen deposition on Rs, Ra, and Rh in urban-rural forests. Our finding indicated a positive association between soil temperature and Rs. Soil temperature sensitivity was significantly suppressed in the experimental plots treated with 100 kg·ha−1·year−1 of nitrogen only in terms of the urban forest Rs and Ra and the rural forest Ra. Nitrogen treatment did not significantly increase Rs and had different influencing mechanisms. In urban forests, nitrogen addition contributed to Rh by increasing soil microbial biomass nitrogen and inhibited Ra by increasing soil ammonium‑nitrogen concentration. In suburban forests, the lack of response of Rh under nitrogen addition was due to the combined effects of soil ammonium‑nitrogen and microbial biomass nitrogen; the indirect effects from nitrate‑nitrogen also contributed to a divergent effect on Ra. In rural forests, the soil pH, dissolved organic C, fine root biomass, and microbial biomass C concentration were the main factors mediating Rs and its components. In summary, the current rate of nitrogen deposition is unlikely to result in significant increases in soil C release in urban-rural forests, high nitrogen deposition is beneficial for reducing the temperature sensitivity of Rs in urban forests. The findings grant a groundwork for predicting responses of forest soil C cycling to global change in the context of urban expansion.

Impacts of Climate change on soil microbial diversity, distribution and abundance

Climate change, driven by anthropogenic activities, has far-reaching consequences for our planet. Among its many impacts, changes in temperature, elevated carbon dioxide levels, and shifts in greenhouse gas concentrations significantly affect soil ecosystems. In particular, soil microbial communities play a pivotal role in nutrient cycling, organic matter decomposition, and overall soil health. Soil microbial communities respond differently to the effects of climate change, like elevated warming and precipitation. The change in climatic conditions is reported to be adversely affecting soil biological activity directly through either drying or wetting of soil or affecting their associated plants. This review delves into the intricate relationship between climate change and soil microbial abundance, diversity, and distribution. The paper also discusses climatic change pressure on soil enzymatic activity and microbial biomasses, as well as soil faunal activity, as they are key indicators of soil health in a changing climate. Soil microbial communities cope with climate change by changing their diversity and physiological characteristics and by changing their symbiotic plants, which indicates the role of soil microbes in withstanding the negative impact of climate change.

Effect of Different Organic Sources on Seed Yield of rabi Fennel (Foeniculam vulgare P. Mill.) under Organic Farming

The present study is titled “Effect of different organic sources on seed yield of rabi fennel (Foeniculam vulgare P. Mill.) under organic farming. It was carried out at Agronomy Instructional Farm of the Chimanbhai Patel College of Agriculture, Sardarkrushinagar Dantiwada Agricultural University, Sardarkrushinagar, Gujarat during Rabi season of the year 2015-16, 2016-17 and 2019-20. Foeniculum vulgare, commonly known as fennel, is a widely recognized and essential medicinal and aromatic plant from the Apiaceae family. This study also examines the impact of organic sourcess in fennel cultivation, highlighting their potential to improve soil structure and microbial biomass. Organic sources, derived from both animal and plant sources, are considered eco-friendly alternatives with long term benefits. Results from the study indicate that for growing rabi fennel under organic farming application of 75% RDN (67.5 kg N/ha) either through castor cake or FYM at the time of sowing along with seed inoculation with Azotobacter and PSB @ 5 ml/kg seed for obtaining higher seed yield and net returns. These findings suggest the potential of organic manures to improve the growth and yield of fennel. In conclusion, this provides an extensive overview of fennel, addressing its botanical characteristics, chemical composition, pharmacological attributes, traditional uses, and agricultural practices. The experimental data highlights the positive impact of organic manures on fennel growth parameters, offering valuable insights for sustainable cultivation practices.

Arbuscular mycorrhizal fungi attenuate negative impact of drought on soil functions.

Although positive effects of arbuscular mycorrhizal (AM) fungi on plant performance under drought have been well documented, how AM fungi regulate soil functions and multifunctionality requires further investigation. In this study, we first performed a meta-analysis to test the potential role of AM fungi in maintaining soil functions under drought. Then, we conducted a greenhouse experiment, using a pair of hyphal ingrowth cores to spatially separate the growth of AM fungal hyphae and plant roots, to further investigate the effects of AM fungi on soil multifunctionality and its resistance against drought. Our meta-analysis showed that AM fungi promote multiple soil functions, including soil aggregation, microbial biomass and activities of soil enzymes related to nutrient cycling. The greenhouse experiment further demonstrated that AM fungi attenuate the negative impact of drought on these soil functions and thus multifunctionality, therefore, increasing their resistance against drought. Moreover, this buffering effect of AM fungi persists across different frequencies of water supply and plant species. These findings highlight the unique role of AM fungi in maintaining multiple soil functions by mitigating the negative impact of drought. Our study highlights the importance of AM fungi as a nature-based solution to sustaining multiple soil functions in a world where drought events are intensifying.

Factors driving microbial biomass and necromass relationships display ecosystem‐dependent responses

AbstractMicroorganisms help govern soil organic carbon (SOC) turnover and accumulation. Whilst it is increasingly clear that microbial necromass is a precursor of SOC formation, the relationship between living microorganisms, necromass turnover and SOC persistence remains elusive. In this study, we used phospholipid fatty acids and amino sugars to quantify living versus dead microbial carbon concentrations and evaluated the utility of each pool as an indicator of SOC persistence across a range of climates (low‐, mid‐ and high‐latitude sites) and ecotypes (old‐growth forests vs. managed croplands). We found that microbial necromass was higher in forest than in cropland soils and was positively correlated with soil moisture, SOC and total nitrogen (TN). However, the flow of microbial biomass into necromass and SOC was decoupled in forest sites, likely because the high soil SOC/TN ratio accelerated necromass turnover and recycling by living microorganisms. In contrast, microbial biomass and necromass pools were tightly coupled in croplands and influenced by multiple environmental and biological factors (e.g., necromass concentrations exhibited greater variability in soils with more bacteria than fungi, and those with more gram‐positive than gram‐negative taxa). Contrasting our expectations, the proportion of microbially‐derived necromass in SOC was decoupled from soil properties and microbial biomass in both ecotypes. Whilst SOC and pH appear to be universal drivers of necromass cycling, feedbacks between living biomass, necromass and SOC are shaped by local factors. Our results contribute to ecological theory by highlighting the environmental and biological factors underpinning SOC formation and turnover that can be used to inform land‐management practices that optimize below‐ground carbon sequestration.

Soil biological fertility evolution in a chronosequence under long‐term rice cultivation after land reclamation in China

AbstractLand use significantly affects soil biological fertility through impacts on carbon (C) and nitrogen (N) cycling. The present study investigated the effects of long‐term rice cultivation after tidal flat reclamation on soil C and N metabolism, microbial biomass and biological fertility. Eighteen composite topsoil (0–20 cm) samples were identified in a chronosequence of coastal reclamation areas (0–700 years old) in subtropical monsoon climate zone, namely tidal flat (T0), salt marsh soil (S10) and paddy soil (P50, P100, P300 and P700). Using ANOVA analysis, mono‐exponential regression model, and multiple linear regressions, soil organic matter (SOM), total nitrogen (TN), cumulative C mineralization content (Ct) and N mineralization content (Nt), basal soil respiration (BSR) and microbial biomass C and N (MBC and MBN) in the P50‐P700 samples were significantly higher than those in the T0 and S10 samples, whereas C metabolic quotients (qCO2) in the P50‐P700 were significantly lower than those in the T0 and S10 samples. The time to steady state for SOM and TN are 357 years and 80 years, respectively; 133 and 221 years for Ct and Nt, respectively; and 318 and 183 years for MBC and MBN, respectively. Also, a soil biological fertility index (SBFI) was calculated on the basis of SOM, BSR, Ct, MBC, qCO2 and qCM. P100‐P300 samples had the highest SBFI score (28.7) and ranked in the class V (very high) of biological fertility, achieving steady‐state conditions after 146 years. SBFI was significantly positively correlated with SOM, TN, MBC, MBN, BSR, Ct and Nt, whereas it was significantly negatively correlated with pH, qCO2 and C mineralization quotient (qCM). MBC and qCM were two independent variables with considerable positive effects on SBFI. Long‐term rice cultivation could facilitate C and N accumulation and enhance biological fertility in soils via microbial activity, especially within 300 years. Our findings demonstrate that rice cultivation has the potential to enhance soil C and N accumulation. Carbon‐related SBFI is suitable for assessing soils under long‐term rice cultivation, mainly because the rice paddy field is an intensive and conservative system.

Non-linear responses of the plant phosphorus pool and soil available phosphorus to short-term nitrogen addition in an alpine meadow

Nitrogen (N) enrichment is expected to induce a greater phosphorus (P) limitation, despite the acceleration of soil P cycling. However, the changing patterns in plant P and soil available P after N enrichment, and their regulatory mechanisms, remain poorly understood in alpine meadows. Here, we conducted a field experiment with four N addition rates (0, 5, 10, and 15 g N m-2 yr-1) in an alpine meadow, and investigated the P in plants, microorganisms, and soil to determine their patterns of change after short-term N addition. Our results showed that N addition significantly increased plant biomass, and the plant P pool showed a non-linear response to the N addition gradient. Soil available P initially increased and then declined with increasing N addition, whereas the occluded inorganic P decreased markedly. The critical factors for soil available P varied with different N addition rates. At lower N addition levels (0 and 5 g N m-2 yr-1), soil acidification facilitated the mobilization of occluded inorganic P to increase soil available P. Conversely, at higher N addition levels (10 and 15 g N m-2 yr-1), the elevated soil microbial biomass P intensified the competition with plants for soil P, leading to a decline in soil available P. This study highlights the non-linear responses of the plant P pool and soil available P concentration to N addition rates. These responses suggest the need for developing ecosystem models to assess different effects of increasing N rates, which would enable more accurate predictions of the plant P supply and soil P cycling under N enrichment.

Canopy and understory nitrogen additions differently affect soil microbial residual carbon in a temperate forest.

Atmospheric nitrogen (N) deposition in forests can affect soil microbial growth and turnover directly through increasing N availability and indirectly through altering plant-derived carbon (C) availability for microbes. This impacts microbial residues (i.e., amino sugars), a major component of soil organic carbon (SOC). Previous studies in forests have so far focused on the impact of understory N addition on microbes and microbial residues, but the effect of N deposition through plant canopy, the major pathway of N deposition in nature, has not been explicitly explored. In this study, we investigated whether and how the quantities (25 and 50 kg N ha-1 year-1) and modes (canopy and understory) of N addition affect soil microbial residues in a temperate broadleaf forest under 10-year N additions. Our results showed that N addition enhanced the concentrations of soil amino sugars and microbial residual C (MRC) but not their relative contributions to SOC, and this effect on amino sugars and MRC was closely related to the quantities and modes of N addition. In the topsoil, high-N addition significantly increased the concentrations of amino sugars and MRC, regardless of the N addition mode. In the subsoil, only canopy N addition positively affected amino sugars and MRC, implying that the indirect pathway via plants plays a more important role. Neither canopy nor understory N addition significantly affected soil microbial biomass (as represented by phospholipid fatty acids), community composition and activity, suggesting that enhanced microbial residues under N deposition likely stem from increased microbial turnover. These findings indicate that understory N addition may underestimate the impact of N deposition on microbial residues and SOC, highlighting that the processes of canopy N uptake and plant-derived C availability to microbes should be taken into consideration when predicting the impact of N deposition on the C sequestration in temperate forests.

Termite mound soil based potting media: a better approach towards sustainable agriculture.

Termite mound soils are known to possess unique physico-chemical and biochemical properties, making them highly fertile. Considering their rich nutrient content, the objective of the current experiment is to assess the physico-chemical properties and enzyme activities of termite mound based potting media and evaluate theirperformance for further exploration in floriculture. Potting media consisting of termite mound soil (TS) of a subterranean termite, Odontotermes obesus were prepared in 7 different combinations with garden soil (GS), sand (S) and farmyard manure (FYM) and a control (without termite mound soil), i.e., T1 (TS, GS, S, FYM (v:v:v:v /1:2:1:1)), T2 (TS, GS, S, FYM (v:v:v:v / 2:1:1:1)), T3 (TS, S, FYM (v:v:v / 2:1:1)), T4 (TS, GS, FYM (v:v:v / 2:1:1)), T5 (TS, GS, S (v:v:v / 2:1:1)), T6 (TS, S, FYM (v:v:v / 3:1:1)), T7 (TS, S, FYM (v:v:v / 1:1:2)) and control (GS, S, FYM (v:v:v / 2:1:1)). The samples were then analysed in laboratory. Experimental analysis on physico-chemical and biological parameters revealed superiority of T7 (TS, S, FYM (v:v:v / 1:1:2)) in terms of pH (7.15), organic carbon (2.13%), available nitrogen (526.02 kg ha-1), available phosphorus (56.60 kg ha-1), available potassium (708.19 kg ha-1), dehydrogenase activity (18.21 μg TTF g-1 soil day-1), Phosphomonoesterase (PME) activity (46.68 54 μg p-nitrophenol/gsoil/h) and urease activity (3.39 μg NH4-N g-1 soil h-1). Whereas T4 (TS, GS, FYM (v:v:v /2:1:1)) registered superiority in terms of PME activity (50.54 μg p-nitrophenol/gsoil/h), Fluorescein diacetate (FDA) activity (11.01 μgfluorescein/gsoil/h) and Soil Microbial Biomass Carbon (SMBC) (262.25 μg/g). Subsequent to the laboratory analysis, two best potting mixtures (T7 & T4) were selected and their performance was assessed by growing a test crop, Tagetes erecta cv. Inca Orange. Considering the growth parameters, the potting media: T7 was found to be significantly superior in terms of plant spread (39.64 cm), leaf area index (4.07), fresh weight (37.72 g), yield (317.81 g/plant), and diameter (9.38 cm) of flower over T4 & control. The Benefit:Cost (B:C) ratio meaning the ratio of net returns to total cost of cultivation was determined. The B:C ratio of raising marigold flower as potted plant in T7 was 1.10 whereas the B:C ratio of the potting mixture of T7 was 2.52. This shows that T7 potting media is also economically viable choice for commercial purposes.