Afforestation-driven soil organic carbon stabilization in a hyper-arid desert: nonlinear dynamics and microbial...

Desertification and soil carbon loss threaten arid ecosystem sustainability, yet the long-term stability of soil organic carbon (SOC) following afforestation in hyperarid regions remains poorly understood. Here, we investigated SOC dynamics across a 22-year Populus alba chronosequence at the Taklimakan Desert edge, combining physical fractionation particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) with microbial phospholipid fatty acid (PLFAs) and enzymatic analyses. Afforestation significantly increased SOC content by 50.97 %-108.05 %, with MAOC surging 100.94 %-160.59 % after 22 years (P < 0.01). SOC stability (MAOC/POC ratio) peaked at 12 years before declining. Random forest modeling identified total nitrogen (TN) and available phosphorus (AP) as key drivers. Meanwhile, microbial metabolic limitations, assessing by the stoichiometric of soil extracellular enzymes, shifted from phosphorus (P) limitation to carbon-phosphorus (C-P) colimitation suppressed decomposition activity, enhancing SOC stability. This study provides the quantification of nonlinear SOC stability trajectories in hyperarid plantations, offering critical insights for optimizing afforestation age to enhance the stability of SOC. Our findings advance mechanistic understanding of SOC persistence in water-limited ecosystems and directly inform desertification control policies under climate change scenarios.