Abstract: The increase of nitrogen (N) deposition would obviously disturb the soil respiration, further make important influences on the carbon (C) budget and C sequestration in the terrestrial ecosystem. Taking a subtropical Pinus elliottii Plantation in China as the research object, a quantitative study about the responses of the root autotrophic respiration, microbial heterotrophic respiration to the varying N availability was conducted by field simulation control experiment based on the distinction of different components of soil respiration, and a preliminary discussion on the biogeochemistry and microbiological mechanism of the response were also made. Results showed that:(1) The dynamic characteristics of the total soil respiration, root respiration and microbial respiration displayed obvious single peak curve in both 2015 and 2016, with the maximum respiration rates observed in July or August. Simulated N deposition had no significant influence on the seasonal pattern of soil respiration rates. (2) The annual average rates of the total soil respiration, root respiration and microbial respiration were 3.91, 2.30 and 1.73 μmol/(m²·s), respectively under CK (0), LN treatment (60 kg/(hm²·a)) and HN treatment (120 kg/(hm²·a)); The annual average root respiration and microbial respiration of CK, LN, HN were 1.41, 0.87, 0.66 μmol/(m²·s) and 2.50, 1.44, 1.07 μmol/(m²·s), respectively. The total soil respiration and its two components were inhibited obviously under simulated N deposition, and the total soil respiration, root respiration and microbial respiration all decreased obviously along with the increase of N input levels. (3) Under CK treatment, the proportion of microbial respiration to total soil respiration (P_m) was 65.2%, but under LN and HN treatments, the P_m values were decreased significantly with 62.6% and 62.1%. The N input showed a greater inhibitory effect on microbial respiration than on root respiration. A year after N application, the inhibitory effect of N input on soil respiration was declining. (4) N application had no significant effect on the contents of total organic carbon (TOC), NH₄⁺, NO₃^-, dissolved organic carbon (DOC), dissolved organic nitrogen (DON), microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) in surface soil at the depth of 0-10 cm. Simulated N deposition reduced soil pH value, acidized surface soil of P. elliottii Plantation, inhibited the activities of soil urease and soil invertase significantly, and futher affected soil microbial activity, which resulted in the reduction of soil microbial respiration. This may be the key mechanism for the response of soil respiration to N addition in this study.