Responses of temperate steppe to simulated nitrogen deposition: from community structure to ecosystem functions

Effect of nitrogen deposition on terrestrial ecosystems are one of the hot spots in the study of global change, and the significantly different responses were reported widely among different ecosystems. In this study, field simulated nitrogen deposition experiment was carried out in a temperate steppe, norther China from 2011 to 2018. Treatments were designed as: CK (0 g N/m²), N2 level (2 g N/m²), N5 level (5 g N/m²), N10 level (10 g N/m²), N25 level (25 g N/m²) and N50 level (50 g N/m²). The results showed that the N addition did not cause a noticeable change in the net primary productivity and soil acidification. N addition caused a significant decline in community biodiversity with a major shift in species composition. N utilization strategy, photosynthetic capacity, and water use efficiency of three dominant species behaved differently under N deposition. Soil was the major sink for N deposition testified by the ¹⁵N isotope tracer experiment. N addition decreased soil microorganism and plant ¹⁵N recovery and increased soil of 30-40 cm layer ¹⁵N recovery. N saturation of the temperature steppe would occur when N deposition rate reached 5.4-8.4gN m^-2a^-1.