氮添加对红松人工林草本层植物多样性的影响

氮沉降是驱动生物多样性变化的重要因素之一。为了探索氮添加对红松（Pinus koraiensis）人工林草本层植物多样性的影响及其驱动机制，以黑龙江凉水国家级自然保护区红松人工林为研究对象，设置N0（对照处理，0 kg hm^-2 a^-1）、N20（低氮处理，20 kg hm^-2 a^-1）、N40（中氮处理，40 kg hm^-2 a^-1）和N80（高氮处理，80 kg hm^-2 a^-1）4个施氮水平，进行6年的氮添加实验。结果表明：（1）氮添加显著降低草本层3个功能群的密度和盖度，而对高度无显著影响；（2）6年氮添加使对照与施氮处理间群落相似度随施氮水平的增加而减小；（3）氮添加显著降低草本植物的丰富度和Shannon-Wiener多样性指数，而未对蕨类和木本植物的丰富度和Shannon-Wiener多样性指数产生显著影响，对草本层3个功能群的Pielou均匀度指数均无显著影响；（4）氮添加对草本植物的C、N、P含量、N：P、C：P产生显著影响，对木本植物的P含量、N：P、C：P产生显著影响，对蕨类植物的C：N：P生态化学计量均无显著影响；（5）草本植物多样性与土壤化学性质无显著的相关关系，草本植物丰富度、Shannon-Wiener多样性指数与植物盖度、密度呈显著的正相关关系，丰富度与植物N含量呈显著的负相关关系，Shannon-Wiener多样性指数与植物N：P呈显著的负相关关系。研究表明6年氮添加改变植物草本层中物种组成和群落结构，3个功能群密度和盖度显著降低，高度未产生显著变化，仅降低草本植物的丰富度和多样性。造成该现象的原因可能是，不同物种对于氮的利用特性和耐受程度存在差异，氮添加引起草本植物养分失衡，改变物种组成和群落结构，从而影响草本植物多样性。研究结果可为我国温带森林生态系统持续性管理提供数据和理论基础。

Effects of nitrogen addition on species diversity of the understory plants in the Korean pine plantation

Nitrogen deposition is one of the important driving factors of biodiversity change. To explore the effect of nitrogen addition on the understory plants diversity of the Korean pine (Pinus koraiensis) plantation and its driving mechanism, we simulated N deposition with four levels of N addition rate N0 (control treatment, 0 kg hm^-2 a^-1), N20 (low nitrogen treatment, 20 kg hm^-2 a^-1), N40 (medium nitrogen treatment, 40 kg hm^-2 a^-1) and N80 (high nitrogen treatment, 80 kg hm^-2 a^-1) for 6 years, based on the Korean pine plantation in Liangshui National Nature Reserve in Heilongjiang Province. The results showed that:(1) nitrogen addition significantly reduced the density and coverage of the three functional groups in the understory plants, but had no significant effect on the height. (2) The 6-year nitrogen addition reduced community similarity between control and nitrogen application treatment decreased with the increase of nitrogen application level. (3) Nitrogen addition significantly reduced the Shannon-Wiener diversity index and species richness of herbs in the Korean pine plantation. Nitrogen addition had no significant effect on the species richness and Shannon-Wiener diversity index of woody plants and ferns. Nitrogen addition had no significant effect on the Pielou evenness index of the three functional groups of herbs. (4) Nitrogen addition had significant effects on the contents of C, N, P, N:P and C:P of herbs. Nitrogen addition had significant effect on the contents of P, N:P and C:P of woody plants, and it had no significant effect on C:N:P ecological stoichiometry of ferns. (5) There was no significant correlation between herb diversity and soil chemical properties. There was significantly positive correlation between species richness of herbs, Shannon Wiener index and coverage, density of herbs. There was significantly negative correlation between species richness of herbs and plant N content, and between herb Shannon Wiener index and plant N:P. The 6-year nitrogen addition changed the species composition and community structure in the understory plants, significantly reduced the density and coverage of the three functional groups, and had no significant change on the height, and it only reduced the species richness and Shannon-Wiener diversity index of herbs. The reason for this phenomenon may be that different species have different nitrogen utilization characteristics and tolerance, and nitrogen addition causes nutrient imbalance of herbs, changes species composition and community structure, and affects herbs diversity. The results provide data and theoretical basis for the sustainable management in temperate forest ecosystems in China.