Elevated silicon concentrations accelerate decomposition of the dominant silicon-rich grass litter in grassland ecosystems

Litter decomposition is a fundamental process in terrestrial carbon (C) cycling, influencing atmospheric CO₂ levels, soil organic matter formation, and nutrient turnover. While nitrogen (N) concentration and C/N ratios have traditionally been considered primary drivers of decomposition, how other factors such as silicon (Si) concentration affect litter decomposition remains poorly understood, particularly in grassland ecosystems. We conducted a concurrent pot experiment with N and Si additions in the laboratory, along with a multi-point sampling field experiment, to obtain litter samples with varying N and Si concentrations in grasses and legumes. Two subsequent incubation experiments using natural ¹³C tracing techniques were performed to explore litter biodegradability and the formation of new soil C. Our results showed that short-term N addition did not significantly affect litter biodegradability for either grass or legume species. In contrast, Si addition significantly increased the biodegradability of grass litter by 12.1 % and marginally enhanced the formation of new soil C in grasses. Grass litter biodegradability was positively correlated with Si concentration and Si-related stoichiometric ratios (Si/C, Si/N, Si/phenol, and Si/lignin), but not with traditional metrics such as C/N or lignin/N ratios. These results suggest that Si plays a critical role in regulating decomposition of the Si-rich grass litter. Our findings highlight the need for further research to elucidate the mechanisms by which Si influences litter decomposition and soil C formation, with implications for understanding grassland ecosystem functioning under global change scenarios.