模拟氮沉降对长白山岳桦林下草本植物和土壤肥力的短期影响

选取长白山岳桦林中的岳桦-蟹甲草群落（Comm.Betula ermanii-Parasenecio forrestii）、岳桦-藜芦群落（Comm.Betula ermanii-Veratrum nigrum）和岳桦-小叶章群落（Comm.Betula ermanii-Deyeuxia purpurea）开展野外模拟氮沉降实验，采用野外原位模拟实验方法，设置对照（0 kg·hm^-2·a^-1）、低氮（30 kg·hm^-2·a^-1）、中氮（50 kg·hm^-2·a^-1）和高氮（100 kg·hm^-2·a^-1）4个氮处理水平，测定草本植物生长状况和土壤肥力，研究岳桦林下草本层植物和土壤肥力对氮沉降的短期响应。结果显示：（1）岳桦林下草本植物随氮沉降量的增加而加速生长，小叶章对氮沉降的响应较为敏感，藜芦次之，蟹甲草最弱；（2）氮添加造成林下土壤肥力发生变化，有机质含量下降，特别是岳桦-小叶章群落下的土壤有机质含量下降最明显；土壤总氮和速效氮含量增大，岳桦-蟹甲草群落下的土壤总氮和速效氮增加最多；土壤总磷和速效磷含量减小，岳桦-小叶章群落下的土壤总磷和速效磷含量的减少最多。本研究结果表明氮添加在短期内会促进长白山岳桦林下草本植物生长，尤其是小叶章的生长，加快土壤有机质的分解和磷的释放，逐步改变土壤肥力并反馈给植物，促使其进一步变化。

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.