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 C-13 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 C-13 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 C-13 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.