Xianjun Jiang

Tea plantations are one of the most intensive land-use systems in subtropical China, but the long-term effects on soil microbial functioning remain insufficiently understood. This study combined extracellular enzyme activity, ecoenzymatic stoichiometry, and partial least squares path modeling (PLS-PM) to assess the impacts of forest-to-tea conversion and plantation age on microbial nutrient acquisition and metabolic limitations. The results showed that tea plantations had significantly higher activities of carbon (C)-, nitrogen (N)-, and phosphorus (P)-acquiring hydrolases compared to adjacent pine forests, and oxidase activity increased significantly with plantation age, reaching a fivefold higher level in the oldest plantation. Soil acidification, decreased soil organic carbon, and shifts in microbial composition (decline in bacteria and actinomycetes, increase in fungi) were the main drivers of these changes. The study indicates that tea planting intensifies microbial limitations on carbon and phosphorus and shifts microbial metabolism toward oxidative pathways, which may destabilize soil carbon pools and reduce long-term fertility. These findings highlight the importance of balanced nutrient management in tea plantation practices. However, the study is limited by the short duration of field sampling. Future research should focus on long-term monitoring to better understand the sustained impacts of tea cultivation on soil microbial functions and explore the role of different management practices in mitigating these effects.

Introduction: Small molecule metabolites can act as soil conditioners to improve the soil environment and thereby promote crop growth. Like many other components of root exudates, succinic acid not only contributes to plant growth and stress resistance but also influences microbial growth in soil, thereby participating in the carbon cycle. Succinic acid is believed to act as a signaling molecule that bridges the host plant and microorganisms during their interactions. However, the mechanism by which succinic acid affects microbes, metabolites and their interaction in soil remains unclear.Methods: High-throughput sequencing and pseudotargeted metabolomics techniques were applied for exploring the effects of succinic acid in tobacco-planting soil and corresponding tobacco chemical composition.Results: The addition of succinic acid improved the soil chemical properties for increasing the available potassium, total nitrogen, total phosphorus and total potassium, and had a positive impact on soil fertility. In the microbial communities, fungi were more sensitive to succinic acid than bacteria. The relative abundance of Proteobacteria in the bacterial community was significantly decreased, while that of Chloroflexi was significantly increased. The relative abundances of Actinobacteriota and Acidobacteriota also showed a decreasing trend. The relative abundances of Ascomycota and Basidiomycota in the fungal community increased significantly, while the relative abundance of Chytridiomycota decreased significantly. The microbial function prediction indicated that 0.4% succinic acid may affected the nutrients and carbon-nitrogen cycles. In the soil metabolomics, the absolute contents of monosaccharide, disaccharide, sugar alcohol and trehalose in soil metabolites increased significantly. The 47 characteristic metabolites were significantly enriched in amino acid metabolism and carbohydrate metabolism. Correlation analysis showed that soil microbes were mainly positively correlated with amino acids and sugars. In addition, the relative abundances of monosaccharide, disaccharide and sugar alcohol increased in tobacco leaf, while alkaloid and amino acid decreased for improving the tobacco chemical composition.Conclusion: This study demonstrated that the addition of succinic acid affected soil chemical property, microbial communities and the composition of soil metabolites, and then improved crop chemical components.

Whether nitrogen (N)-metabolic versatility is a common trait of N-transforming microbes or if it only occurs in a few species is still unknown. We collected 83 soil samples from six soil types across China, retrieved 19 publicly available metagenomic marine sample data, and analyzed the functional traits of N-transforming microorganisms using metagenomic sequencing. More than 38% and 35% of N-transforming species in soil and marine ecosystems, respectively, encoded two or more N-pathways, although N-transforming species differed greatly between them. Furthermore, in both soil and marine ecosystems, more than 80% of nitrifying and N-fixing microorganisms at the species level were N-metabolic versatile. This study reveals that N-metabolic versatility is a common trait of N-transforming microbes, which could expand our understanding of the functional traits of drivers of nitrogen biogeochemistry.

Nitrogen (N) fertilizers are increasingly being used to meet crop demand for the expanding human population. However, historical N‐use efficiency (NUE) is low for rice paddy fields compared to upland ecosystems. This study aimed to investigate the fate of N fertilizer and compared NUE under different tillage regimes in a rice‐based agroecosystem. A long‐term field study of tillage regimes (i.e. flooded paddy field, conventional tillage and ridge tillage) and ¹⁵ N isotope tracer methods (in situ and incubation) was used to determine N fertilizer fate and uptake. Nitrogen uptake by rice (which represents NUE) significantly differed between tillage regimes ( p < .05). Nitrogen‐use efficiency was 31% of applied N fertilizer for ridge tillage, which was the highest among the three tillage regimes, while the lowest NUE occurred for conventional tillage (17%). The soil residual N for ridge tillage was significantly higher (21%), than for the flooded paddy field or conventional tillage. The total gaseous N loss was highest for ridge tillage (28%) and lowest for conventional tillage (17%). Ammonia (NH ₃ ) volatilization accounted for the largest proportion of gaseous loss from N fertilizer for all three tillage regimes. However, the largest loss of applied N was with water (runoff and leaching), where N loss accounted for 20% of applied N for ridge tillage but up to 54% for conventional tillage. Ridge tillage changed the soil micro‐topography and water regimes leading to better N conservation. Based on these results, adoption of ridge tillage should significantly improve NUE for rice paddy fields.

Ammonia oxidizing bacteria (AOB), Ammonia oxidizing archaea (AOA) and methane oxidizing bacteria (MOB) play cogent roles in oxidation and nitrification processes, and hence have important ecological functions in several ecosystems. However, their distribution and compositional differences in different long-term flooded paddy fields (FPFs) management at different soil depths remains under-investigated. Using qPCR and phylogenetic analysis, this study investigated the abundance, niches, and compositional differences of AOA, AOB, and MOB along with their potential nitrification and oxidation rate in three soil layers from three FPFs (ShaPingBa (SPB), HeChuan (HC), and JiDi (JD)) in Chongqing, China. In all the FPFs, CH₄ oxidation occurred mainly in the surface (0–3 cm) and subsurface layers (3–5 cm). A significant difference in potential methane oxidation and nitrification rates was observed among the three FPFs, in which SPB had the highest. The higher amoA genes are the marker for abundance of AOA compared to AOB while pmoA genes, which is the marker for MOB abundance and diversity, indicated their significant role in the nitrification process across the three FPFs. The phylogenetic analysis revealed that AOA were mainly composed of Nitrososphaera, Nitrosospumilus, and Nitrosotalea, while the genus Nitrosomonas accounted for the greatest proportion of AOB in the three soil layers. MOB were mainly composed of Methylocaldum and Methylocystis genera. Overall, this finding pointed to niche differences as well as suitability of the surface and subsurface soil environments for the co-occurrence of ammonia oxidation and methane oxidation in FPFs.