Effect of N addition and litter manipulation on plant community productivity in the semiarid sandy grassland

Plant community productivity is a major expression of grassland ecosystem services and functions. In the background of intensified atmospheric nitrogen deposition, studies on the productivity of semiarid sandy grassland with fragile ecological environments have mainly focused on the short-term effects of nitrogen addition, and most of them had concentrated on the aboveground, with relatively few studies on the belowground. In this study, we conducted long-term (from 2014 to 2022) experiment of nitrogen addition (10 g N m(-2) year(-1)) and litter manipulation (litter removal(C1), litter doubling(C2) on sandy grassland in northern China, and measured plant community composition and productivity in 2022 to provide a scientific basis for plant restoration and management of semiarid sandy grasslands. The results were found: (1) Nitrogen addition significantly increased plant community height, coverage, aboveground biomass and total biomass, while litter removal significantly reduced plant coverage by 32.61% (P < 0.01) and significantly decreased the aboveground biomass of grasses by 40.24% (P < 0.05). (2) Nitrogen addition and aboveground litter had no significant effect on belowground biomass at different soil depths and belowground biomass. (3) Grasses were the main contributors to the productivity of plant communities in semiarid sandy grasslands. The belowground biomass was mainly concentrated in the 0-10 cm soil depth, and its proportion was 54% similar to 78%. (4) The structural equation model showed that nutrient addition indirectly affected the total biomass through a significantly positive effect on soil nitrate nitrogen, dissolved organic carbon and community height. Litter manipulation indirectly affected the total biomass through a significantly negative effect on nitrate nitrogen. Overall, in sandy grassland, long-time litter removal can reduce the aboveground productivity of dominant functional group grasses, while appropriate nitrogen addition management can help to improve the productivity of grassland and promote its recovery and sustainability. Our findings highlight the importance of soil environmental characteristics and plant community characteristics in driving the long-term response of sandy grassland ecosystem productivity to climate change.