Nitrogen input drives carbon flow in desert ecosystems: mechanisms of photosynthetic carbon allocation response to nitrogen deposition

Against the backdrop of continuously increasing global nitrogen (N) deposition, the changes in photosynthetic carbon (C) allocation patterns of desert plants and their underlying mechanisms affecting soil C sequestration remain poorly understood. This study selected two representative species from desert ecosystems: the non-vascular moss Syntrichia caninervis and the vascular ephemeral plant Erodium oxyrhinchum as research subjects. Three N deposition levels were implemented: 0 (N0), 10.0 (N10), and 30.0 kg N ha^-1 a^-1 (N30), combined with ¹³C stable isotope labeling technique, to systematically investigate the effects of N deposition on plant photosynthetic C allocation and soil C sequestration. The experiment demonstrated that: (1) Aboveground ¹³C content in both species decreased significantly with increasing N input (P < 0.05); (2) N deposition significantly promoted photosynthetic C transfer to soil, with soil ¹³C allocation increasing from 0.8% (N0) to 4.0% (N30) for S. caninervis, and from 5.0 to 12.2% for E. oxyrhinchum (P < 0.01). N deposition alters photosynthetic C allocation strategies in desert plants, significantly enhancing belowground C transfer and strengthening soil C sink function. This study provides crucial experimental evidence for evaluating arid region C cycle dynamics under global N deposition scenarios.