Tracing Rhizodeposition Contributions to Soil Organic Carbon under Long-Term Tillage in a Wheat–Maize System Using Stable Isotope Labeling

Transferring photosynthetic C to soil organic C (SOC) via rhizodeposition is essential for soil health and soil C sequestration. This study employed ¹³C isotope labeling to quantify rhizodeposition C transfer and examined its relationship with soil properties and microbial communities in a 15-year long-term tillage experiment. The treatments included no-tillage (NTS), plow tillage (CTS), and rotary tillage (RTS), all implemented with straw return. The results showed that the rhizodeposition C transfer and microbial community compositions varied between wheat and maize. Rhizosphere-specific taxa, such as Galbitalea in wheat and Priestia in maize, were enriched under NTS. Compared to CTS, RTS increased rhizosphere ¹³C-SOC by 65% in wheat, while NTS increased it by 99% in maize, thereby enhancing rhizodeposition C transfer. Furthermore, NTS facilitated fungal community stability and DOC turnover, collectively promoting rhizodeposition C transfer. Optimizing crop-specific tillage strategies can enhance C transfer, improve soil health, and mitigate climate change.