Decades of no-till coupled with warming improves topsoil soil organic matter accrual via stimulating microbial carbon use efficiency

Conservation tillage such as no-till has been recommend as a potential strategy to sequester soil organic matter (SOM) and mitigate climate change, but how this alternative farming altered SOM biochemistry remains elusive, particularly under simulated warming condition. Here, we uncovered the SOM composition and origins, and underlying microbial-mediated processes from a conservation tillage trial under warming in North China. Soil samples (i.e., 0-5, 5-15, and 15-30 cm) were collected from four treatments: moldboard plow (MP), moldboard plow with warming (MPw), no-till (NT), and no-till with warming (NTw). Considering tillage effects, NTw (cf. MPw) increased both bacterial and fungal biomass in topsoil. Further, NT (cf. MP) decreased oligotrophic K-strategists, including Chloroflexi and Gemmatimonadetes. Regardless of warming, no tillage enhanced the relative abundance of recalcitrant dissolved organic matter (DOM), but decreased biodegradable DOM compounds such as carbohydrates, proteins in topsoil. Both biomarker (higher total lignin phenols) and ¹³C-nuclear magnetic resonance (higher aromatic and phenolic group) collectively revealed the enhanced preservation of lignin phenols in NTw (cf. MPw). No tillage (NT and NTw) significantly increased glomalin-related soil protein (GRSP) in the surface soil, while warming have no effects on those molecules. Moreover, NT enhanced bacterial and fungal necromass relative to MP in the topsoil. Considering warming effects, warming decreased catabolic enzymes activities (β-1,4-glucosidase and leucine aminopeptidase) under two tillage systems, while exerted the strong positive influence on microbial carbon use efficiency. Collectively, NTw (cf. MPw) may have the potential to enhance the process of bacterial anabolism and in vivo turnover (reflecting by microbial necromass and GRSP), thus improve microbial carbon pump efficiency and OM formation in a future warmer world. Moreover, no-till treatments (NT, NTw) increased the fraction of refractory DOM (i.e., condensed aromatic structures and tannin) relative to conventional farming. Our work provides insights into the potential benefits of conservation agriculture for long-term carbon sequestration because no tillage improves resilience to the effects of climate warming.