*2.1. Study Sites*

This study was conducted at the Qianyanzhou Ecological Research station in Taihe County, Ji'an City, Jiangxi Province, China (115◦0329.2" E, 26◦4429.1" N). The research site is a typical red hilly region with subtropical monsoonal climate. The annual average precipitation is up to 1600 mm and the annual average temperature is approximately 18 ◦C [41]. The experimental site is within the native distribution of Chinese fir. The study was conducted in an experimental Chinese fir plantation that was established approximately 15 years ago. The coverage of the sample plot was between 75 and 85%, and the slope was between 20 and 30◦. The natural atmospheric N deposition in this area was 49 kg N ha−<sup>1</sup> year<sup>−</sup><sup>1</sup> [42].
