近日，中科院华南植物园生态系统管理创新研究组鲁显楷博士和莫江明研究员等在鼎湖山国家级自然保护区开展的最新研究发现：大气氮沉降通过诱导土壤酸化效应，引起“富氮”（N-rich）森林生态系统的植物多样性显著减少。
当今学术界普遍认为，大气氮沉降将降低“氮限制”（N-limited）生态系统的生物多样性而对“富氮”生态系统的影响则甚微。以上观点主要来源于“竞争排斥机制”（Competitive exclusion mechanism）理论以及在温带和北方地区（通常为“氮限制”的生态系统）开展的相关研究。该理论认为，在“氮限制”的生态系统中，氮的增加更有利于喜氮植物种类的生长，使其在竞争中处于优势从而排斥其它物种，最终导致生物多样性的降低；而在“富氮”的生态系统中，因植物长期适应“富氮”状态，氮的增加对植物生长的影响不大。
此项研究首次报道了氮沉降对“富氮”森林的植物多样性的影响，其结果不仅填补了国际上热带和亚热带区域氮沉降对森林植物多样性影响研究的空白，同时表明了氮沉降可能威胁“富氮”森林的植物多样性。
该成果已在线发表在全球变化研究领域的权威杂志Global Change Biology 上。(生物谷Bioon.com)
生物谷推荐原文出处：
Global Change Biology DOI 10.1111/j.1365-2486.2010.02174.x
Effects of experimental nitrogen additions on plant diversity in an old-growth tropical forest
XIANKAI LU * , JIANGMING MO * , FRANK S. GILLIAM?, GUOYI ZHOU * and YUNTING FANG *
Response of plant biodiversity to increased availability of nitrogen (N) has been investigated in temperate and boreal forests, which are typically N-limited, but little is known in tropical forests. We examined the effects of artificial N additions on plant diversity (species richness, density and cover) of the understory layer in an N saturated old-growth tropical forest in southern China to test the following hypothesis: N additions decrease plant diversity in N saturated tropical forests primarily from N-mediated changes in soil properties. Experimental additions of N were administered at the following levels from July 2003 to July 2008: no addition (Control); 50 kg N ha?1 yr?1 (Low-N); 100 kg N ha?1 yr?1 (Medium-N), and 150 kg N ha?1 yr?1 (High-N). Results showed that no understory species exhibited positive growth response to any level of N addition during the study period. Although low-to-medium levels of N addition (≤100 kg N ha?1 yr?1) generally did not alter plant diversity through time, high levels of N addition significantly reduced species diversity. This decrease was most closely related to declines within tree seedling and fern functional groups, as well as to significant increases in soil acidity and Al mobility, and decreases in Ca availability and fine-root biomass. This mechanism for loss of biodiversity provides sharp contrast to competition-based mechanisms suggested in studies of understory communities in other forests. Our results suggest that high-N additions can decrease plant diversity in tropical forests, but that this response may vary with rate of N addition.
