Biochar is useful for soil organic carbon (SOC) sequestration. However, the effects of biochar aging and addition rates on SOC stabilization are unclear. A field experiment with four biochar application rates (0% (control), 1% (LB), 2% (MB), and 4% (HB) of dry fluvo-aquic soil) was conducted. Soil samples were sampled after 8, 12, and 24 months of its application to clarify the question. In general, SOC gradually increased with the biochar application rate. SOC with HB was higher than that in other treatments, while the ratio of microbial biomass carbon (MBC)/SOC and readily oxidizable carbon (ROC)/SOC with HB was lower than that in other treatments (p < 0.05), indicating a positive effect of HB for C stabilization over time. The effects of biochar on the soil carbon pool management index (CPMI) changed from negative to positive after 8 and 24 months of biochar application. The activities of β-D-glucosidase (βG), cellobiohydrolase (CBH), and β-N-acetylglucosaminidase (NAG) under HB were higher than with other treatments after 12 and 24 months of biochar application (p < 0.05) and negatively correlated with the ratio of MBC/SOC and ROC/SOC over time. The CPMI was positively related with βG and CBH activities after 8 and 24 months of biochar application, respectively (p < 0.05). HB increased the relative abundance of oligotrophs, including Acidobacteria, Actinobacteria, and Chloroflexi, but decreased the relative abundance of copiotrophs, including γ-Proteobacteria and Bacteroidetes over time (p < 0.05). The ratio of dissolved organic carbon (DOC)/SOC was positively correlated with the bacterial oligotroph/copiotroph ratio and significantly affected the oligotrophic and copiotrophic bacterial communities, especially after 8 and 12 months of biochar application (p < 0.05). These findings reinforce that increasing the biochar application rate and time enhances SOC stabilization by decreasing the proportions of labile organic carbon and making oligotrophic/copiotrophic communities and enzyme activities more conducive to C sequestration.

Female panicles (FPs) play an important role in the formation of yields in maize. From 40 days after sowing to the tasseling stage for summer maize, FPs are developing and sensitive to drought. However, it remains unclear how FPs respond to drought stress during FP development. In this study, FP differentiation was observed at 20 and 30 days after drought (DAD) and agronomic trait changes of maize ears were determined across three treatments, including well-watered (CK), light drought (LD), and moderate drought (MD) treatments at 20, 25, and 30 DAD. RNA-sequencing was then used to identify differentially expressed genes (DEGs) in FPs at 30 DAD. Spikelets and florets were suppressed in LD and MD treatments, suggesting that drought slows FP development and thus decreases yields. Transcriptome analysis indicated that 40, 876, and 887 DEGs were detected in LD/CK, MD/CK, and MD/LD comparisons. KEGG pathway analysis showed that ‘biosynthesis of other secondary metabolites’ and ‘carbohydrate metabolism’ were involved in the LD response, whereas ‘starch and sucrose metabolism’ and ‘plant hormone signal transduction’ played important roles in the MD response. In addition, a series of molecular cues related to development and growth were screened for their drought stress responses.

Identifying the potential factors associated with the impact of long-term drip irrigation (DI) on soil ecosystems is essential for responding to the environmental changes induced by extensive application of DI technology in arid regions. Herein, we examined the effects of the length of time that DI lasts in years (N_DI) on soil bacterial diversity as well as the soil bacterial community assembly process and the factors influencing it. The results showed that long-term DI substantially reduced soil salinity and increased soil bacterial diversity while affecting the soil bacterial community structure distinctly. Null model results showed that the soil bacterial community assembly transitioned from stochastic processes to deterministic processes, as N_DIincreased. Homogeneous selection, a deterministic process, emerged as the dominant process when N_DIexceeded 15 years. Both random forest and structural equation models showed that soil salinity was the primary factor affecting the bacterial community assembly process. In summary, this study suggested that soil bacteria respond differently to long-term DI and depends on the N_DI, influencing the soil bacterial community assembly process under long-term DI.

The impacts of rhizosphere microorganisms on the turnover of nutrients are affected by many environmental factors. In this study, rice plants were subjected to deep flooding and heat stress for one week at the jointing stage. Rhizospheric soil was sampled for the analysis of rice rhizosphere bacterial assembly and functional groups responsible for carbon and nitrogen transformation. Compared with the control, both deep flooding and heat stress increased bacterial alpha diversity. Moreover, heat stress and the interactions of heat stress and deep flooding improved the bacterial cooperation. Heat stress reduced the relative abundance of Actinobacteria and Firmicutes, which are responsible for organic carbon decomposition. The relative abundance of the gene encoding lignin-degrading catalases under deep flooding and heat stress treatments reduced by 6% and 8%, respectively. The interaction of heat stress and deep flooding increased the relative abundance of the nifD gene by 5%, may slowed down nitrate reduction to nitrite. Our results highlight the effects of heat and flooding stress on the bacteria-mediated mechanisms responsible for regulating organic carbon sequestration and nitrogen cycling in rhizosphere of paddy fields.

Exploring the impact of subsurface drainage on microbial community structures in saline-alkali soils is of great significance for maintaining the sustainability of saline-alkali fields. In this study, seven field treatments were designed in cotton fields: two drain depth (0.8 and 1.1 m) and three drain spacing (10, 20, and 30 m) treatments, as well as no drainage (control). Soil samples were obtained in the seedling and flowering and boll-setting (FBS) stages, and the soil properties and microbial communities (bacteria and fungi) were analyzed. The results displayed that compared with the control group, soil salt was significantly decreased in all subsurface drainage treatments. Subsurface drainage treatments have no effect on microbial richness and diversity. Both drain depth and spacing had significant effects on bacterial and fungal composition structures in the seedling stage, but only drain depth significantly altered soil microbial composition structures in the FBS stage. Based on the null model, the assembly of soil microbial communities was mainly driven by stochastic processes. The contributions of the deterministic process for soil bacterial community assembly at the seedling stage and FBS stage were 18.1% and 22.1%, respectively. In contrast, soil fungal community assembly was mainly determined by dispersal limitation and drift.

The global demand for cotton makes sustainable cotton production an important issue that can be improved by a better understanding of the influence of soil microbes on cotton growth. We collected cotton field soils at the seedling and flowering/boll-setting (FBS) stages in order to obtain soil properties and cotton growth indices. Bacterial and fungal community compositions were assessed by high-throughput sequencing of 16S rRNA and internal transcribed spacer genes, respectively, after which the differences in microbial functions and their influencing factors at different growth stages were analyzed. Both the diversity and composition of soil bacterial and fungal communities were found to be significantly different between the seedling and FBS stages. Microbes in the seedling stage had significantly higher richness and biomass than those in the FBS stage. Compared with the seedling stage, the stability of the soil bacterial communities was decreased. The cotton growth indices at both the seedling and FBS stages were associated with compositional shifts in the bacterial community and but not the fungal community. The abundance of specific soil microbial taxa (e.g., Pseudarthrobacter, Thiobacillus, Cephalotrichum, Chaetomium, and Fusarium) were correlated with cotton growth indices at the seedling stage, being mainly regulated by soil salinity and nitrate content. Our results highlight the importance of soil microbial communities in mediating cotton growth and will be useful in providing better strategies for the improvement of cotton agriculture.