关键词: 氮添加, 围封草地, 刈割草地, 土壤呼吸, 自养呼吸, 异养呼吸

Abstract: Soil respiration, a pivotal process of the carbon cycle in terrestrial ecosystems, comprises autotrophic respiration (R_a) and heterotrophic respiration (R_h), and is influenced by land use patterns and environmental changes. However, the response of soil respiration to grassland utilization patterns under the background of nitrogen (N) deposition remains unclear. In this study, we examined the effects of N addition on the rates of soil respiration (R_s) and its components (R_a and R_h) in long-term enclosed and mown grasslands during the growing season in the Hui River Basin of Hulunbuir. There were four levels of N addition, including 0 (N0), 2 (N2), 5 (N5), and 10 g·m^-2·a^-1 (N10). The results showed that N addition and grassland utilization patterns did not alter the temporal dynamics of soil respiration rate, with peak values observed in July-August. Nitrogen addition and grassland utilization patterns significantly affected R_s, R_a, and R_h (P<0.05), while had no effects on the ratio of R_a/R_h (P>0.05). Furthermore, there was no interactive effect of N addition and grassland utilization patterns in affecting soil respiration rate (P>0.05). The N2 treatment did not affect R_s or R_a (P>0.05). However, the N5 treatment significantly increased R_s (by 13.8% and 13.1%) and R_a (by 29.8% and 28.3%) in both enclosed and mown grasslands, respectively (P<0.05). The N10 treatment significantly increased R_s (by 7.0%) in mown grassland (P<0.05). Additionally, N addition did not affect R_h in either enclosed or mown grasslands (P>0.05). Mowing significantly increased soil respiration rates (P<0.05). R_s in mown grassland was significantly higher than in enclosed grassland under the N0, N5, and N10 treatments, while R_a was significantly higher in mown grassland only under the N0 treatment (P<0.05). Soil moisture was the main regulator of soil respiration and its components under N addition, whereas grassland utilization patterns regulated soil respiration and its components primarily through altering soil temperature and belowground biomass. Compared to fencing, mowing increased the moisture and temperature sensitivity of R_h and R_a. Moreover, N addition in enclosed grasslands enhanced the moisture and temperature sensitivity of R_a and the moisture sensitivity of R_h, but decreased the temperature sensitivity of R_h. In mown grasslands, N addition increased the moisture sensitivity of R_a but decreased its temperature sensitivity. Our results enhance the mechanistic understanding of the responses of soil respiration and its components to N addition and grassland utilization patterns in meadow steppe, which can provide a theoretical basis for the scientific management of grassland ecosystems.

Key words: nitrogen addition, enclosed grassland, mown grassland, soil respiration, autotrophic respiration, heterotrophic respiration