The Effect of Litter Addition on Soil Organic Carbon Fractions with Intensified Grassland Degradation

Litter decomposition plays a critical role in the formation and turnover of soil organic carbon (SOC) and its fractions. However, the effects of litter on SOC dynamics across grassland degradation remain poorly understood. The objectives of this study were to investigate the responses of SOC and its fractions, including particulate organic carbon (POC) and mineral-associated organic carbon (MAOC), to litter decomposition in lightly, moderately, and highly degraded grasslands. A 240-day incubation experiment using Leymus chinensis litter incubated on day 0, 23, 60, and 240 was conducted to investigate the biotic and abiotic factors regulating SOC stability. Grassland degradation significantly reduced POC and MAOC concentrations; moreover, litter addition in degraded grasslands further reduced SOC. In the lightly and moderately degraded grasslands, litter addition modulated POC and MAOC via both microbial and physicochemical pathways. In the highly degraded grasslands, litter addition influenced POC and MAOC not only indirectly through microbial and physicochemical pathways but also directly by promoting MAOC formation. Overall, although litter decomposition altered SOC and its fractions, its effects were constrained by the degree of grassland degradation. These findings indicate that restoration strategies should prioritize enhancing microbial biomass and activity in lightly and moderately degraded grasslands while increasing litter inputs in highly degraded grasslands to improve soil carbon sequestration.