Effects of nitrogen application on soil respiration and its components in a Pinus tabulaeformis plantation

The study site is located in the Ziwuling region (35°03′–36°07′N, 108°10′–109°18′E) on the Loess Plateau, China. In September 2015, a 40-year-old P. tabulaeformis plantation was chosen as the research site. The experiment included four N application levels: no N (CK), low N (LN), medium N (MN), and high N (HN), corresponding to 0, 5, 10, and 20 g N m−2 a−1, with three replicates per level. N fertilization, applied as granular urea (46% N). In September 2019 and September 2020, all annual samples were collected prior to N application, and relevant physicochemical factors were subsequently determined. Rs and its components were measured at September 2019 and September 2020 using a portable infra-red gas analyzer (LI-COR 8100) with soil chamber (LI-COR Inc., USA).