Long-term cover cropping mitigates the soil carbon saturation deficit by accumulating plant-derived POC and microbial-derived MAOC in an apple orchard - Tongtong Guan; Pengpeng Li; Shuangcheng Wang; Narasinha Shurpali; Muhammad Kamran; Yuan Ma; Yuying Shen; Yan Zhang (Soil and Tillage Research, 2026)