Short-term effects of simulated nitrogen deposition on herbaceous plants and soil fertility in the Betula ermanii Cham. forest of Changbai Mountain

To investigate the effects of nitrogen deposition on herb-layer plants and soil fertility in a Betula ermanii Cham. forest, we carried out simulated nitrogen deposition experiments on the B. ermanii-Parasenecio forrestii, B. ermanii-Veratrum nigrum, and B. ermanii-Deyeuxia purpurea communities in the B. ermanii forest of Changbai Mountain. We established control (0 kg·hm^-2·a^-1), low nitrogen (30 kg·hm^-2·a^-1), medium nitrogen (50 kg·hm^-2·a^-1), and high nitrogen (100 kg·hm^-2·a^-1) treatment gradients to assess the status of herbaceous plants and soil fertility. Results suggested that:(1) Growth of herbaceous plants in the B. ermanii forest was accelerated by nitrogen addition, with B. ermanii-D. purpurea being the most sensitive, followed by B. ermanii-V. nigrum, and B. ermanii-P. forrestii. (2) In regard to changes in soil fertility caused by nitrogen deposition, soil organic matter decreased, especially in the B. ermanii-D. purpurea community. In addition, total and available nitrogen increased, whereas total and available phosphorus decreased with the increase in nitrogen addition. Total and available nitrogen increased most in the B. ermanii-P. forrestii community, whereas total and available phosphorus decreased most in the B. ermanii-D. purpurea community. Thus, we concluded that nitrogen addition could promote the growth of the understory herbaceous plants in the B. ermanii forest, especially D. purpurea, and accelerate the decomposition of soil organic matter and release of phosphorus, which could gradually change soil fertility and further influence plant growth.