Soil-borne Fusarium wilt disease causes damage to certain crops, but crop rotation may be an effective management strategy for this pest. Soil microbes may play an important role in this strategy, but the response of the soil microbial community to crop rotation is unclear. In a field experiment, we used high-throughput sequencing to study the effects of banana rotation with one of four other crops (pepper, sugarcane, wax gourd and pumpkin) or continuous cultivation of banana as a single crop on soil microbial community. Compared with monocropping, all crop rotation strategies led to a decrease in the incidence of Fusarium wilt of banana, while an increase in banana yields. The main bacterial phyla were Proteobacteria (24.96%), Acidobacteria (21.25%), Gemmatimonadetes (12.98%), and the fungal phyla was Ascomycota (72.54%), across the soil. These four crop rotation treatments also increased bacterial richness and the relative abundance of Acidobacteria, Gemmatimonadetes, Firmicutes, and Actinobacteria, while reducing the relative abundance of Proteobacteria, Chloroflexi, Parcubacteria, Cyanobacteria and Fusarium. Redundancy analysis showed that soil pH, organic matter and available phosphorus were the main factors affecting the composition of bacterial and fungal communities. Overall, we show that crop rotation can inhibit banana wilt and change soil microbial community composition.

Most studies about the effects of N addition on soil microbial biomass evaluate soil microbial and physicochemical characteristics using single-test methods, and these studies have not been integrated and analyzed to comprehensively assess the impact of N fertilization on soil microbial biomass. Here, we conduct a meta-analysis to analyze the results of 86 studies characterizing how soil microbial biomass C (MBC), N (MBN), and P (MBP) pools respond to exogenous N addition across multiple land use types. We found that low N addition (5–50 kg/hm²) rates significantly affect soil microbial biomass, mainly by increasing MBC but also by decreasing MBP and significantly increasing MBC/MBP. N addition affects soil physicochemical properties, significantly reducing pH and significantly increasing the soil dissolved organic N and inorganic N content. Our analysis also revealed that the effects of N application vary across ecosystems. N addition significantly decreases MBP and total P in planted forests but does not significantly affect soil microbial biomass in grasslands. In farmland soil, N addition significantly increases total P, NH₄⁺, NO₃⁻, MBN, and MBP but significantly decreases pH. Although N addition can strongly influence soil microbial biomass, its effects are modulated by ecosystem type. The addition of N can negatively affect MBC, MBN, and MBP in natural forest ecosystems, thereby altering global ecosystem balance.

Organic and inorganic nitrogen play important roles in plant nitrogen nutrition. However, how the coapplication of organic and inorganic nitrogen affects root growth, plant nitrogen metabolism, and soil nitrogen content is still unclear. Plant shoot and root growth, nitrogen uptake and metabolism, and soil nitrogen content were studied in maize (Zea mays L.) through pot experiments with different nitrogen treatments, including NH₄⁺ -N (Amm), NO₃⁻ -N (Nit), NH₄⁺ -N + NO₃⁻ -N (Amm + Nit), NH₄⁺ -N + NO₃⁻ -N + glutamate-N (Amm + Nit + Glu), and NH₄⁺ -N + NO₃⁻ -N + glycine-N (Amm + Nit + Gly). The results show that the shoot nitrogen uptake of maize treated with Amm + Nit + Gly was the highest among all the nitrogen treatments. In addition, the coapplication of glycine and inorganic nitrogen increased glutamine synthetase (GS) activity in the maize leaves, promoted nitrogen metabolism levels, and was conducive to the accumulation of amino acids and soluble protein in leaves. Compared with inorganic nitrogen, glycine combined with inorganic nitrogen increased the total root length and root surface area. A correlation analysis showed that total root length and root surface area had a significant positive effect on nitrogen uptake. When ammonium, nitrate, and glycine were applied together, the content of inorganic nitrogen and total nitrogen in soil was higher than that for other inorganic nitrogen treatments. Therefore, we conclude that glycine combined with inorganic nitrogen can increase soil nitrogen content, promote maize root growth, and thus facilitate nitrogen uptake and metabolism.

The use of biochar and lime (CaO) is a common approach to mitigating soil acidification. However, little is known about how biochar and lime amendments impact N₂O emissions and potential microbial mechanisms. We conducted a 45-day microcosm incubation experiment to examine N₂O emission and associated functional guilds to biochar and lime amendment in an acidic tea plantation soil. Results show that lime and biochar treatments significantly reduced cumulative N₂O emissions by 49.69% and 63.01%, respectively, while significantly increasing cumulative CO₂ emissions by 27.51% and 19.35%, respectively. Additionally, lime and biochar treatments significantly decreased the abundances of bacterial nirK, nirS, nosZ and fungal nirK genes, while increasing that of the ammonia-oxidizing bacteria (AOB) and the complete ammonia-oxidizing bacteria (comammox) amoA genes. The stimulated or inhibitory effects of biochar on functional genes abundances were higher than lime. The N₂O emission rate was positively linked with the abundance of the fungal nirK gene but was negatively correlated with AOB and comammox amoA genes abundances. The random forest and linear regression analysis revealed that fungal denitrifiers were the most important predictors of N₂O emissions. Lime and biochar amendments reduced the alpha diversity and altered the community composition of nirK-harboring fungal denitrifiers. Ascomycota was the dominant fungal denitrifiers belonging to the families Nectriaceae, Aspergillaceae, and Chaetomiaceae, and the relative abundances of genera Chaetomium, Penicillium and Fusarium were positively correlated with N₂O emissions. Overall, our findings suggest that biochar is more effective than lime in reducing N₂O emissions, and this is likely due to the powerful effects it has on community traits of nirK-harboring fungal denitrifiers.

Soil amendments have been extensively employed for the purpose of remediating soils contaminated with cadmium (Cd). However, the potential impacts of soil amendments on soil chemical properties, soil Cd bioavailability, total Cd accumulation by rice, and rhizosphere bacterial community in Cd-contaminated paddy fields located in a tropical region is still at its infancy. In this study, a commercial MgO-CaO-SiO₂ conditioner (A), biochar (B), and a combination of the commercial MgO-CaO-SiO₂ conditioner and biochar with a ratio of 1:1 (C) were applied at two different doses [2250 kg ha⁻¹ (A150, B150, C150), 4500 kg ha⁻¹ (A300, B300, C300)] to investigate their impacts on soil Cd stabilization and total Cd uptake of rice straw and grain in a Cd-contaminated remediation field experiment. Rhizosphere bacterial community diversity and composition were also assessed using high-throughput sequencing based on 16S rRNA genes. Compared with non-amendment treatment (CK), soil pH, cation exchange capacity (CEC), organic matter (OM), total nitrogen (TN), available nitrogen (AN), and nitrate (NO₃⁻) concentrations were significantly elevated, whereas ammonium (NH₄⁺) and soil available Cd concentrations were reduced by soil amendment treatments. Meanwhile, soil amendments significantly decreased concentrations of total Cd in both rice straw and grain, with the lowest Cd concentration in the C300 treatment. Soil pH and CEC were significantly and negatively associated with soil Cd availability and rice straw and grain Cd concentrations, while NH₄⁺ concentration was positively correlated with soil available Cd concentration, and OM, TN, and NO₃⁻ concentrations were positively linked with rice grain Cd concentration. Soil amendments significantly increased bacterial Chao 1 and Shannon indexes and altered bacterial community composition in rhizosphere soil, due to changes in the composition of the community primarily influenced by variations in soil pH, CEC, and soil available Cd, NH₄⁺, available phosphorous (AP) and available Potassium (AK) concentrations. Furthermore, the abundant bacterial species (Pseudomonas) and rare bacterial species (Bacillus, Candidatus_Solibacter and Streptomyces) have been up-regulated by different soil amendments, which might be in favour of soil Cd immobilization. A structural equation model also showed that soil amendments could improve bacterial diversity and change soil pH and CEC, which were conducive to hindering the removal and conversion of Cd. Overall, these results indicate that biochar-(MgO-CaO-SiO₂) mixed amendments at high dosage exerted better performance compared with single application soil amendment A and B. The changes in soil chemical properties, available Cd content, and rhizosphere bacterial community assembly induced by soil amendments are closely correlated with the decrease in rice’s ability to accumulate Cd.