地下生态系统中氮素的循环及影响因素

The nitrogen cycle and factors affecting it in the belowground ecosystem

氮素是陆地生态系统初级生产力的主要限制因子之一。地下生态系统中绝大部分氮素以不溶的聚合物形式存在,不能直接被植物吸收,因此其转化为可吸收的离子氮的生态过程受到人们越来越多的关注。本文主要综述了土壤生物与非生物两个自然因素在地下生态系统氮素循环过程中发挥的重要作用。土壤生物通过自身代谢和分泌各种酶类来加速各种形态氮素相互转化;植物根系可以通过影响土壤物理结构和分泌大量有机物质,实现与地下生态系统氮素循环之间的"相互交流";而由于生物生存与环境因子有直接联系,二者之间的相互作用也对土壤氮素循环起着特殊作用。目前,由于土壤生物种类繁多、营养流通途径复杂、分子生物学实验技术较昂贵以及在全球气候变化背景下对许多自然规律的响应变化认识有限,因此,尚不能完全在分子水平形成一张氮素在地下生态系统的流通网络图,这应该成为今后相关研究工作的方向和重点。

Nitrogen（N）is one of the main factors limiting primary productivity in terrestrial ecosystems due to its role in plant growth and development.In belowground ecosystems,most nitrogen exists in the form of complex polymers,but these forms of nitrogenous compounds cannot be absorbed and assimilated directly by plants.Hence,the ecological process from complex polymers to simple inorganic substances has always been a focus of research;this process is regulated and controlled by a series of complex biogeochemical reactions that occur belowground via symbiotic associations between plant roots and bacteria（e.g.,biological nitrogen fixation）.In this paper,we summarize the effects of soil biotic and abiotic factors on the belowground nitrogen cycle.Soil organisms promote the belowground nitrogen cycle through metabolism and release of various enzymes;Plant roots change the soil properties and secrete organic matter.The development of soil organisms is strongly restricted by abiotic factors,so the interaction between organisms and some abiotic factors also exerts important influences on the belowground nitrogen cycle.Currently,due to the high abundance of soil organism species,the complexity of nutrient circulation patterns,the limited understanding regarding the response of nature to global climate change,and the expense of molecular biotechnology,it is still difficult to define the whole nitrogen nutrition circulation network in the belowground ecosystem at the molecular level.This review summarizes our current understanding regarding the belowground nitrogen cycle and how it is regulated by biotic and abiotic factors.