Biology and Fertility of Soils最新文献

Soil gross mineral N production and consumption processes are crucial regulators of plant productivity and N loss from croplands. Substituting synthetic fertilizers by integrating legumes in cultivation systems is common in organic farming, but research on its long-term impact on dynamics of gross soil N transformation and associated environmental N loss is scarce. In particular, studies at a temporal resolution that allows for a mechanistic understanding of long-term effects of organic farming are missing. Therefore, we determined gross N turnover rates of ammonification, nitrification, and ammonium and nitrate immobilization at monthly temporal resolution during a full green rye-maize cropping sequence. Measurements were carried out at sites with same pedo-climatic background but organic farming (OF) and integrated farming (IF) history. During green rye growing, N turnover rates for OF and IF were low and not significantly different, likely owing to low temperatures. During silage maize growing, IF exhibited significantly higher average N turnover rates of 1.86, 4.46, and 5.57 mg N kg⁻¹ dry soil d⁻¹ for gross ammonification, ammonium immobilization, and nitrate immobilization, respectively, compared to OF values of 1.11, 1.80, and 2.90 mg N kg⁻¹ dry soil d⁻¹. The significantly higher N turnover rates were likely due to higher soil organic C, N and microbial biomass which result from different long-term management practices. Especially the increased immobilization potential on the IF site contributed to significantly lower area-scaled N₂O emissions (1.45 vs. 4.36 kg N ha⁻¹) during periods of high nitrification. This shows that for low SOC soils, integrated farming history with high C return enhances soil N cycling and reduces the risk of N losses in the form of N₂O emission.

Acetochlor (ACE), one of the widely used herbicides in northeastern China, has raised concerns due to its residual presence in the soil. In this study, a pot experiment was conducted to investigate the effects of adding vermicompost on the degradation efficiency and pathways of acetochlor in black soil under dark conditions. The results showed that the vermicompost addition increased the degradation rate of acetochlor, shortened its degradation half-life, and altered the composition of the bacterial community. The influence of vermicompost on bacterial community diversity is minimal, but it can increase the relative abundance of acetochlor degradation bacteria, promoting the collaboration between exogenous and indigenous bacteria to enhance acetochlor utilization. GC-MS analysis revealed the formation of seven metabolites during the acetochlor degradation process, including 2-chloro-N-(2-ethyl-6-methylphenyl) acetamide, 2-ethyl-6-methylaniline, 4-amino-3-ethyl-5-methylpheno, 2-ethyl-6-methylcychexa-2,5-diene-1,4-diol, 2-ethyl-6-methylcychexa-2,5-diene-1,4-dione, N-(2-ethyl-6-methylphenyl)hydroxylamine and 1-ethyl-3-methyl-2-nitrobenzene. The synergistic action of Sphingomonas, Rhodococcus, Bacillus, Arthrobacter, Methylobacillus, and Streptomyces probably lead to the gradual decomposition of acetochlor into H₂O and CO₂. Comparative analysis of functional genes in the KEGG metabolic pathways showed upregulation of hyaB/hybC, hyaA/hybO, nfsA, nfnB/nfsB, and nemA in the soil treated with vermicompost. These functional genes could promote -NHOH conversion to -NO₂. Additionally, redundancy analysis revealed that soil organic matter and pH were the main driving factors for bacterial community variation. These findings suggest that vermicompost can be used as a bioremediation measure to reduce acetochlor in black soil.

Despite the crucial role of microbial communities in agroecosystem functioning, a clear picture of how nitrogen shapes rhizosphere microbial complexity and community structure across diverse maize lines remains elusive. To address this gap, we conducted 16S amplicon sequencing of the rhizosphere microbial communities across a diverse range of maize inbred lines (305 genotypes) and their F1 hybrids (196 genotypes) cultivated in both low-nitrogen (unfertilized) and high-nitrogen (fertilized) soils. Our findings reveal that N fertilizer treatment had contrasting effects on the rhizosphere microbial communities of inbreds and hybrids. N fertilization increased alpha diversity but decreased the abundance of Pseudomonas taxa in inbred lines, while the opposite was true for hybrids. The proportion of variance determined by plant host factors was also better explained under low-N, demonstrating that N fertilization reduced the influence of the host over the rhizosphere microbial community. Microbial networks revealed significant differences in the number of nodes and clustering coefficients between the rhizosphere microbial communities of inbred and hybrid maize, with these differences being further differentiated by changes in nitrogen levels. Overall, our study reveals the interplay among rhizosphere microbiomes, abiotic stress induced by low soil nitrogen, and plant host factors facilitating the identification of stable microbial communities in response to environmental stress. These findings contribute to the potential engineering of resilient microbial consortia highlighting the importance of the influence of plant genotype and the environment on the rhizosphere microbiome.

Nitrous oxide (N₂O) is one of the most important climate-forcing gases, and a large portion of global anthropogenic N₂O emissions come from agricultural soils. Yet, how contrasting global change factors and agricultural management can interact to drive N₂O emissions remains poorly understood. Here, conducted within a rice–wheat cropping system, we combined a two-year field experiment with two pot experiments to investigate the influences of elevated atmospheric carbon dioxide (eCO₂) and crop straw addition to soil in altering N₂O emissions under wheat cropping. Our analyses identified consistent and significant interactions between eCO₂ and straw addition, whereby eCO₂ increased N₂O emissions (+ 19.9%) only when straw was added, and independent of different N fertilizer gradients and wheat varieties. Compared with the control (i.e., ambient CO₂ without straw addition), eCO₂ + straw addition increased N₂O emission by 44.7% and dissolved organic carbon to total dissolved nitrogen (DOC/TDN) ratio by 115.3%. Similarly, eCO₂ and straw addition significantly impacted soil N₂O-related microbial activity. For instance, the ratio of the abundance of N₂O production genes (i.e., nirK and nirS) to the abundance of the N₂O reduction gene (i.e., nosZ) with straw addition was 26.0% higher than that without straw under eCO₂. This indicates an increased denitrification potential and suggests a change in the stoichiometry of denitrification products, affecting the balance between N₂O production and reduction, leading to an increase in N₂O emissions. Taken together, our results emphasize the critical role of the interaction between the specific agronomic practice of straw addition and eCO₂ in shaping greenhouse gas emissions in the wheat production system studied, and underline the need to test the efficacy of greenhouse gas mitigation measures under various management practices and global change scenarios.

Graphical abstract

Nitric oxide (NO) is a key substance in atmospheric chemistry, influencing the formation and destruction of tropospheric ozone and the atmosphere's oxidizing capacity. It also affects the physiological functions of organisms. NO is produced, consumed, and emitted by soils, the effects of soil NO concentrations on microbial C and N cycling and associated trace gas fluxes remain largely unclear. This study describes a new automated 12-chamber soil mesocosm system that dynamically changes incoming airflow composition. It was used to investigate how varying NO concentrations affect soil microbial C and N cycling and associated trace gas fluxes under different moisture conditions (30% and 50% WFPS). Based on detection limits for NO, NO₂, N₂O, and CH₄ fluxes of < 0.5 µg N or C m⁻² h⁻¹ and for CO₂ fluxes of < 1.2 mg C m⁻² h⁻¹, we found that soil CO₂, CH₄, NO, NO₂, and N₂O were significantly affected by different soil moisture levels. After 17 days cumulative fluxes at 50% WFPS increased by 40, 400, and 500% for CO₂, N₂O, and CH₄, respectively, when compared to 30% WFPS. However, cumulative fluxes for NO, and NO₂, decreased by 70, and 40%, respectively, at 50% WFPS when compared to 30% WFPS. Different NO concentrations tended to decrease soil C and N fluxes by about 10–20%. However, with the observed variability among individual soil mesocosms and minor fluxes change. In conclusion, the developed system effectively investigates how and to what extent soil NO concentrations affect soil processes and potential plant–microbe interactions in the rhizosphere.

Denitrification is a major source of the greenhouse gas N₂O. As a result of spatial heterogeneity of organic carbon, oxygen and nitrate, denitrification is observed even under relatively dry conditions. However, it is unclear whether denitrification potentials of microbial communities exhibit spatial patterns relative to variations in distance to soil pores facilitating oxygen exchange and nutrient transfer. Thus, we determined genetic and process-level denitrification potentials in two contrasting soils, a cropland and a grassland, with respect to the distance to air-filled pores. An X-ray computed tomography aided sampling strategy was applied for precise sampling of soil material. Process-level and genetic denitrification potentials in both soils were spatially variable, and similar with respect to distance to macropores. In the cropland soil, a minor increase of process-level potentials with distance to pores was observed and related to changes in NO₃⁻ rather than oxygen availability. Genetic denitrification potentials after the short-term incubations revealed a certain robustness of the local community. Thus, distance to macropores has a minor impact on denitrification potentials relative to the observed spatial variability. Our findings support the notion that the impact of macropore induced changes of the environmental conditions in soil does not overrule the high spatial variability due to other controlling factors, so that the rather minor proportion of spatial heterogeneity of functional genes and activity potentials related to macropore distances in soil need not be considered explicitly in modelling denitrification.

¹⁵N tracing was carried out on sandy loam soil amended with (i) mineral nitrogen-phosphorus-potassium fertilizer (NPK) alone, (ii) half mineral N and half N from chicken manure (HFC), or (iii) half mineral N and half N from cattle manure (HCM), for 8 years. Cumulative N₂O emissions during incubation were 30.2 µg N kg^− 1 in the NPK treatment, which increased to 37.8 and 51.3 µg N kg^− 1 in the HFC and HCM treatments, respectively. The majority of N₂O emissions in all the treatments were attributed to nitrification (81.0% in the NPK treatment, 83.0% in the HFC treatment, and 85.1% in the HCM treatment). Compared with NPK, HCM treatment caused a significant increase in the gross rate of nitrification, while HFC treatment slightly enhanced the rate of dissimilatory NO₃⁻ reduction to NH₄⁺. Additionally, HFC treatment achieved higher gross rates of organic N mineralization, and both HFC and HCM treatments had higher NH₄⁺ mineralization-immobilization turnover (MI_AT) rates than NPK treatment. The results suggest that application of cattle or chicken manure increased soil NH₄⁺ availability. The gross rate of NO₃⁻ adsorption in the HCM treatment was greater than that in the NPK treatment, while the release of adsorbed NO₃⁻ in the HFC treatment was slower than that in the NPK treatment, indicating that application of cattle or chicken manure lowered the potential for NO₃⁻ leaching in soil. Overall, combining cattle or chicken manure with mineral fertilizer decreased NO₃⁻ availability but increased NH₄⁺ availability, leading to higher N₂O emissions through nitrification. Our results suggest that organic manures should be applied with nitrification inhibitors in sandy loam soil containing low organic carbon to increase soil fertility and mitigate N₂O emissions.

It remains unclear whether microbial carbon limitation exists in the rhizosphere, a microbial hotspot characterized by intensive labile carbon input. Here, we collected rhizosphere soils attached to absorptive and transport roots and bulk soils in three alpine coniferous forests and evaluated the limiting resources of microbes based on the responses of microbial growth (¹⁸O incorporation into DNA) and respiration to full-factorial amendments of carbon, nitrogen, and phosphorus. The results showed that adding carbon enhanced microbial growth and respiration rates in the rhizosphere soils by 1.2- and 10.3-fold, respectively, indicating the existence of carbon limitation for both anabolic and catabolic processes. In contrast, the promoting effects of nutrient addition were weak or manifested only after the alleviation of carbon limitation, suggesting that nutrients were co-limiting or secondarily limiting resources. Moreover, the category and extent of microbial resource limitations were comparable between the rhizosphere of absorptive and transport roots, and between the rhizosphere and bulk soils. Overall, our findings offer direct evidence for the presence of microbial carbon limitation in the rhizosphere.

We investigated the potential of earthworm casts to emit N₂O, hypothesizing that emission levels are influenced by the species of earthworm and their ecological category. This study examined casts a broad taxonomic and ecological coverage of tropical earthworms, i.e., 16 different species across four ecological categories. We quantified the potential nitrification, N₂O production and consumption as well as the abundance of N-related microbial functional groups, including ammonia-oxidizers, nitrite-reducers, and distinct clades of N₂O-reducers, along with casts chemical properties to determine cast organic matter quality and substrate availability. Earthworm casts exhibited significantly higher concentrations of carbon, nitrogen, and nitrate compared to control soil, while humification index were lower. A negative correlation between humification index and potential N₂O production suggests that more labile substrates in the casts promote higher N₂O flux. Net potential N₂O emissions were higher in the casts of 7 out of 16 species compared to control soil, and all species’ casts showed higher gross potential N₂O production, with substantial interspecific variability. The abundance of nitrite and N₂O reducers was significantly higher in the casts and positively correlated with potential N₂O emissions. Casts from epigeic and mixed categories displayed higher carbon and nitrogen content, abundance of nitrite and N₂O reducers, ammonia-oxidizing bacteria, and potential N₂O production compared to anecic and endogeic categories, which exhibited higher values of humification index. Structural equation modeling indicated that gross potential N₂O production was primarily explained by the abundance of nitrite reducers and substrate availability indicators such as humification index and nitrate concentration. Our study demonstrates significant interspecific variability in N₂O potential emissions from a broad range of tropical earthworm casts, influenced by species feeding behavior, microbial communities, and substrate availability.

Soil microbial necromass carbon (C) is a crucial component of the soil organic C pool. The impact of both straw mulching treatments and years on the soil microbial necromass C accumulation remains unclear. We investigated factors driving soil microbial necromass C accumulation and its role in improving yield by analyzing the dynamic response of microbial necromass C, total organic C (TOC) and available nutrients, genes encoding carbohydrate-degrading enzymes and fruit yield of citrus under different straw types of mulching (wheat, rice, oilseed rape, no mulch) from 2019 to 2022. Annual rainfall was the main factor affecting the soil bacterial necromass C (BNC) accumulation. Straw mulching treatments were the main factor affecting the soil fungal necromass C (FNC) accumulation. Increased annual rainfall and high soil moisture levels hindered the soil microbial necromass C accumulation, especially BNC. No correlation was found between BNC and the relative abundance of genes encoding peptidoglycan (bacteria-derived biomass) degrading enzymes. Decreased relative abundance of genes encoding chitin (fungal-derived biomass) degrading enzymes, particularly GH18, favored the accumulation of FNC. Actinomycetes were the most significant contributors of the GH18 gene among microbial phyla. Moreover, oilseed rape and rice mulching treatments reduced the relative abundance of genes encoding enzymes degrading chitin. Microbial necromass C, especially BNC, was key for sustaining TOC, supplying nutrients, and enhancing citrus fruit yield. Our results provide new information for optimizing straw mulch type and application time in citrus orchards to improve soil microbial necromass accumulation.