Long-term precipitation manipulation enhances carbon sink strength and differentially drives C3 / C4 species biomass in a desert steppe: Five-year results

Desert steppe ecosystems are very sensitive to climate change. Although precipitation is known to promote carbon exchange and biomass production, quantitative assessments of C₃/C₄ species dynamics and carbon-water coupling mechanisms under long-term precipitation manipulation remain limited. Here, we conduct a five-year rainfall control experiment in the Stipa breviflora desert in Inner Mongolia, China, employing four treatments: 50 % reduced precipitation, natural precipitation, 50 % increased precipitation, and 100 % (doubled) precipitation. We measured gas exchange in each plot with a portable photosynthesis system Li-6400 and measured aboveground biomass of C₃ and C₄ species during the growing season (May–October). The results demonstrated that elevated precipitation enhanced ecosystem carbon exchange, driven by a linear increase in C₃ species biomass, with a 100 % precipitation increase significantly strengthening carbon sink capacity. Conversely, the carbon sink function of C₄ species declined under drought (reduce precipitation by 50 %). These findings suggest that C₃ biomass dominates carbon-water coupling, while C₄ species buffers drought effects, collectively stabilizing ecosystems under extreme precipitation.