Fertilization makes strong associations between organic carbon composition and microbial properties in paddy soil

Soil microbial carbon and nitrogen limitation constraints soil organic carbon stability in arid and semi-arid grasslands

Microorganisms play dual roles in soil organic carbon (SOC) decomposition and accumulation. Despite advancing insights into their involvement in the carbon cycle, understanding the impact of microbial community structure and physiological traits on SOC stabilization in arid and semi-arid grasslands remains elusive. Here, we analyzed arid and semi-arid grasslands SOC stability by comparing the ratio of mineral-associated organic carbon (MAOC) to particulate organic carbon (POC) across a grassland transect in north-south Ningxia, encompassing various grassland types and a broad climatic gradient (ΔMAP = 450 mm). By combining phospholipid fatty acid (PLFA) analysis, enzyme activity vector models and stoichiometric theory, the influence of soil microbial community compositions, metabolic constraints, and carbon use efficiency (CUE) on SOC stability were explored. Results showed that SOC stability was the lowest in desert areas and decreased with increasing mean annual precipitation (MAP) in other grasslands. Microbial physiological traits, including microbial carbon (C) limitation, nitrogen (N) limitation, CUE, and lignocellulose index (LCI) varied among grasslands, with significantly higher LCI and CUE and lower C and N limitation in steppe desert. The variation of microbial physiological characteristics accounted for 53.28% of the variation in SOC stability. Distinct microbial metabolic limitations were evident in these grasslands, with N and C limitation prevailing and exerting strong negative impacts on CUE. Decreased fungal/bacterial (F/B) ratios also reduced microbial CUE and indirectly diminished SOC stability. In addition, clay content emerges as a major factor influencing the stabilization of SOC across environmental gradients. Collectively, our work suggests that mitigating microbial C and N limitation and enhancing microbial CUE under the influence of MAP and clay content are the key mechanisms governing SOC stabilization in regional grasslands. These findings bear significant implications for understanding microbial-mediated carbon cycling processes in arid and semi-arid grasslands.

Organic amendments alter microbiota assembly to stimulate soil metabolism for improving soil quality in wheat-maize rotation system

Straw retention (SR) and organic fertilizer (OF) application contribute to improve soil quality, but it is unclear how the soil microbial assemblage under organic amendments mediate soil biochemical metabolism pathways to perform it. This study collected soil samples from wheat field under different application of fertilizer (chemical fertilizer, as control; SR, and OF) in North China Plain, and systematically investigated the interlinkages among microbe assemblages, metabolites, and physicochemical properties. Results showed that the soil organic carbon (SOC) and permanganate oxidizable organic carbon (LOC) in soil samples followed the trend as OF > SR > control, and the activity of C-acquiring enzymes presented significantly positive correlation with SOC and LOC. In organic amendments, bacteria and fungi community were respectively dominated by deterministic and stochastic processes, while OF exerted more selective pressure on soil microbe. Compared with SR, OF had greater potential to boost the microbial community robustness through increasing the natural connectivity and stimulating fungal taxa activities in inter-kingdom microbial networks. Altogether 67 soil metabolites were significantly affected by organic amendments, most of them belonged to benzenoids (Ben), lipids and lipid-like molecules (LL), and organic acids and derivatives (OA). These metabolites were mainly derived from lipid and amino acid metabolism pathways. A list of keystone genera such as stachybotrys and phytohabitans were identified as important to soil metabolites, SOC, and C-acquiring enzyme activity. Structural equation modeling showed that soil quality properties were closely associated with LL, OA, and PP drove by microbial community assembly and keystone genera. Overall, these findings suggested that straw and organic fertilizer might drive keystone genera dominated by determinism to mediate soil lipid and amino acid metabolism for improving soil quality, which provided new insights into understanding the microbial-mediated biological process in amending soil quality.