Abstract
The impact of increased deposition of atmospheric nitrogen on forest soil respiration is one of the focal issues amid global climatic changes. However, the impact of increased atmospheric nitrogen deposition on soil respiration (Rs) in the subtropical Abies georgei (Orr) Forest remains unknown. Hence, a 3-year field experiment was conducted in the subtropical Abies georgei (Orr) Forest from 2019 to 2021 to quantify the impact of three forms of nitrogen source ((NH4)2SO4, NaNO3, NH4NO3) at four rates (0, 5, 15, and 30 kg N.ha−1.yr−1) on Rs. We found that at the early stage of nitrogen application (1–9 months), nitrogen addition increased microbial respiration (Rm) and root respiration (Rt) by 10.12% and 8.14% on average, respectively. The increase in Rm and Rt induced by nitrogen deposition resulted in an increase of 18.16% in Rs. At the later stage of the study (18–36 months), nitrogen application resulted in a significant reduction of 17.39% in Rm and an 18.17% reduction in Rs. However, no significant effect on Rt was observed during the later stages of nitrogen deposition. The annual emission flux of Rs increased by 7.23% in the first year, remained unchanged in the second year, and decreased by 4.43% in the third year. Moreover, the results showed that biological (i.e., soil microorganisms and plant roots) and abiotic (i.e., soil temperature and moisture) factors jointly controlled Rs. A structural equation model showed that soil temperature, soil microbial biomass carbon, and nitrogen were the key controlling factors for Rs, Rm, and Rt, respectively. Therefore, these findings suggest that interactions between these drivers, as well as the contributions of Rm and Rt, are necessary for the assessment of the impact of nitrogen deposition on Rs and soil carbon processes in the context of global climate change.
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