Individual and interactive effects of nitrogen addition and drought on carbon uptake and allocation in terrestrial plants

Abstract The increasing frequency of drought events and elevated nitrogen (N) deposition both affect plant carbon (C) utilization, but whether their individual and interactive effects promote, inhibit, or have no effect on C uptake and allocation remains unclear. We conducted a meta-analysis using 1247 observations from 84 published articles to assess how N addition and drought jointly affected plant photosynthesis, biomass allocation, and nonstructural carbohydrates (NSC) allocation. Our results showed that N addition overall increased plant net photosynthetic rate (Pn) and biomass accumulation, but decreased whole plant total NSC storage. Conversely, drought overall decreased Pn and biomass accumulation while increased whole plant total NSC storage. N addition significantly increased aboveground biomass allocation, whereas drought significantly reduced leaf biomass (LB). Although N addition and drought did not have significant interaction on Pn, biomass allocation, and NSC allocation in terrestrial plants, their interaction significantly increased the root biomass of evergreen broadleaf plants, the LB of deciduous broadleaf plants, and the root-to-shoot ratio of annual herbs. In conclusion, N addition and drought had opposite effects on C uptake, biomass accumulation, and NSC storage in terrestrial plants. The interaction of N addition and drought on biomass allocation was affected by plant functional types. This study enhances our understanding of plant C utilization strategies under multiple environmental changes.