In a greenhouse experiment, we examined the behavior of biochar in arable soil to demonstrate that these supplements can boost soil carbon storage, as well as to track changes in microbial biomass and identify the microbial communities that use these biochars. In order to ascertain if biochar can consistently alter soil microbial activities, we studied the impact of biochar combination treatments on 16S rRNA gene diversity. In soil treated with biochar, there was a rise in the relative abundance of taxa belonging to the phyla Actinobacteria and Gemmatimonadetes, despite the overall diversity decreasing with biochar addition. According to all of these observations, pyrogenic carbon has a major effect on the composition of the soil microbial community and enriches keystone taxa within the parent soil microbial community. Certain species experienced increases throughout the biochar-amended incubation period, despite the total diversity declining following biochar amendments. The phyla Actinobacteria and Gemmatimonadetes increased in the relative abundance of bacteria in soil treated with biochar, according to DNA sequencing of these species. In summary, these findings show that biochar significantly impacts the constitution and composition of the soil microbial community and enriches important taxa within the parent soil microbial community.

Quantifying greenhouse gas intensity (GHGI) and soil carbon sequestration is a method to assess the mitigation potential of agricultural activities. However, the effects of different fertilizer amendments on soil carbon sequestration and net GHGI in a rice-wheat cropping system are poorly understood. Here, fertilizer treatments including PK (P and K fertilizers); NPK (N, P and K fertilizers), NPK + OM (NPK plus manure), NPK + SR (NPK plus straw returning), and NPK + CR (NPK plus controlled-release fertilizer) with equal N input were conducted to gain insight into the change of soil organic carbon (SOC) derived from the net ecosystem carbon budget (NECB), net global warming potential (GWP), and GHGI under rice-wheat rotation. Results showed that compared with NPK treatment, NPK + OM significantly increased wheat yield and NPK + SR caused significant increase in rice yield. Meanwhile, NPK + SR and NPK + CR treatments reduced net GWP by 30.80% and 21.83%, GHGI by 36.84% and 28.07%, respectively, which suggested that improved grain production could be achieved without sacrificing the environment. With the greatest C sequestration, lowest GHGI, the NPK plus straw returning practices (NPK + SR) might be the best strategy to mitigate net GWP and improve grain yield and NUE in the current rice-wheat rotation system.

Long-term positioning tests can systematically reveal the evolution characteristics of soil fertility and crop productivity, and reflect the spatiotemporal changes in soil quality and their driving factors. While soil microorganisms mediating nutrient cycling are crucial for maintaining crop productivity and the long-term resilience of agricultural ecosystems, how prolonged use of different fertilization strategies affects their functional capacity remains insufficiently understood. In this study, we applied metagenomic sequencing to investigate how three fertilization treatments, namely (i) N0 receiving only phosphorus (P) and potassium (K) fertilizers, (ii) N250 receiving conventional urea + P and K, and (iii) F250 receiving humic acid urea + P and K, influence soil microbial communities, functional genes related to C and N cycling, and associated soil properties in a long-term field experiment. The F250 treatment significantly increased average annual yields of wheat and maize to 7166.21 kg hm⁻² and 8309.96 kg hm⁻², respectively. These values were 148.66% and 73.47% higher than those under N0, and 8.22% and 11.64% higher than those under N250. Compared with N0, both N250 and F250 signally augmented soil nitrate, ammonium, total nitrogen (TN), and soil organic carbon (SOC), altered microbial community composition, and enhanced the relative abundance of genes engaged in C fixation and methane oxidation. Both treatments also promoted denitrification and dissimilatory nitrate reduction to ammonium (DNRA). Relative to N250, F250 specifically enriched the beneficial bacterial genus Pedobacter, further increased the abundance of the C fixation gene pccA, and markedly upregulated the DNRA gene nrfA. Soil TN and SOC were identified as the key environmental factors regulating microbial community structure and the functional potential of C and N cycling pathways. Collectively, our findings provide a mechanistic understanding of how long-term application of humic acid urea enhances crop productivity by modulating the genetic potential of soil microorganisms in biogeochemical cycles, offering a biological foundation for optimizing fertilization strategies in sustainable agriculture.

The decomposition of crop residue is indispensable for carbon (C) cycling in agricultural ecosystems, and nitrogen (N) application has a pronounced effect on this by regulating the C/N ratio and microbial growth strategy. This study investigated how different inorganic and organic nitrogen sources interact with soil properties to regulate straw decomposition, nutrient release, microbial community assembly, and microbial interaction networks across typical cropland soils of the North China Plain. Five treatments, i.e., no N addition, urea, calcium nitrate, yeast derivatives, and glutamate, were conducted in fluvo-aquic soil, lime concretion black soil, cinnamon soil, and yellow-cinnamon soil. We found that soil type strongly regulated straw decomposition dynamics, with cumulative decomposition rates varying greatly among the four soil types after 180 days, ranging from 55.78% to 68.75%. In particular, the lime concretion black soil exhibited the highest straw decomposition and C release rates, which harbored higher relative abundances of potential straw-decomposing taxa, including Luteibacter, Chitinophaga, Dothideomycetes, and Leotiomycetes. Bacterial community assembly shifted from stochastic dominance at early stages to deterministic selection at later stages, whereas fungal community assembly remained predominantly stochastic with increasing dispersal limitation during late decomposition. The dominant bacterial phyla were Proteobacteria and Bacteroidota, and the fungal community composition succeeded from Alternaria, Rhizopus, Cladosporium and Meyerozyma to Chaetomium, Schizophecium and Apodus. Compared with no N addition, yeast derivatives significantly increased the straw decomposition rate in fluvo-aquic soil, lime concretion black soil, and cinnamon soil by 15.00, 10.66, and 12.19 percentage points, respectively, within 14 days. This is related to the enhanced complexity of the bacterial co-occurrence network, among which Altererythrobacter, Sphingomonas, Candidatus_Xiphinematobacter, Devosia, and Chitinophaga were identified as key microbial groups. Glutamate stimulated later decomposition by modifying the fungal community structure and strengthening fungal interactions centered on Alternaria and Schizothechium. These findings reveal how N forms regulate straw decomposition through soil-dependent microbial assembly and interaction networks, providing a mechanistic basis for optimizing nitrogen management strategies for efficient straw nutrient recycling.