氮添加对森林植物磷含量的影响及其机制

氮沉降对森林生态系统磷循环产生了不可忽视的影响, 尤其是加剧了植物生长的磷限制, 从而使得氮沉降背景下植物磷含量变化备受关注。该文综述了氮添加对森林植物磷含量的影响, 认为氮添加通过促进土壤磷酸酶活性进而提高土壤有效磷含量, 有利于植物的磷吸收并增加植物磷含量。同时, 森林植物磷含量对氮添加的响应还受物种、生活型以及施氮时间长短等因素的影响。基于森林植物磷含量对氮添加响应的差异性, 该文进一步探讨氮富集背景下森林植物磷含量变化的可能机制: 1)外源氮输入通过改变土壤中有效磷含量从而对植物磷的来源产生影响; 2)通过影响植物的根系分泌物、菌根共生和根系形态结构等进而影响植物的磷吸收能力; 3)通过影响植物的磷养分再分配、磷养分重吸收对植物磷利用效率产生影响。综上所述, 外源氮输入使植物磷含量发生改变, 首要原因是土壤有效磷含量的改变, 其次是植物磷吸收能力和磷利用效率的改变起调控作用。

Impacts of nitrogen addition on plant phosphorus content in forest ecosystems and the underlying mechanisms

Nitrogen (N) deposition has profound impacts on the phosphorus (P) cycling in forest ecosystems. Especially, the aggravated P limitation on tree growth under N addition has caused much attention to researchers. This article reviews the effects of N addition on plant P content in forest ecosystems. The result showed that N addition increased soil available P and facilitated the absorption of P by plants by promoting soil phosphatase activity, thereby increasing plant P content. Furthermore, changes in tree P content following N addition were also affected by species, life forms as well as experimental duration. Due to the inconsistency, the underlying mechanisms of changes in P content under N addition were further summarized as follows: 1) changes in soil available P content induced by exogenous N input affected the source of plant P; 2) N input affected the P uptake capacity of plants by affecting plant root exudates, mycorrhizal symbiosis and root morphological structure; 3) plant P utilization efficiency was also influenced with changes of P re-distribution and P re-absorption. Overall, for the changes in plant P under increasing exogenous N inputs, alterations of soil available P under N addition was the primary factor, while changes in plant P uptake capacity and P utilization efficiency ulteriorly regulated plant P content.