陆地生态系统植物多样性对矿质元素输入的响应

人类活动的加剧改变了陆地生态系统矿质元素(如氮、磷、钾等)循环的速度和方向,并且对生态系统的结构和功能也产生重要影响。如今,矿质元素输入量的改变及其产生的后续效应对陆地生态系统生物多样性的影响备受学者们的关注。从4个方面综述了全球氮沉降背景下主要矿质元素输入的改变对陆地植物多样性的影响及其机理:1)矿质营养元素限制的概念、确定方法以及与植物多样性的耦合关系;2)概述了氮、磷、钾等主要矿质元素输入对陆地植物多样性的影响:主要表现为负面效应;3)探讨了矿质元素输入影响植物多样性的可能机制,包括生态系统水平上的机制(如竞争排斥、酸化铝毒、物种入侵、同质性假说,间接诱导机制等)和植物个体水平上的机制(如元素失衡和环境敏感性增加等);4)根据目前研究现状,指出了已有研究的局限性,分析了未来可能的研究方向和重点。

Responses of terrestrial plant diversity to elevated mineral element inputs

Biodiversity is the basis for ecosystems normal functioning and for the existence and development of human beings. During the past decades, however, anthropogenic activities have greatly altered the direction and magnitude of mineral elements (such as nitrogen N], phosphorus P], and potassium K]) cycling in terrestrial ecosystems, causing great impact on the structure and functioning of these systems and further declining biodiversity therein. It is projected that N deposition will become the third largest driver of biodiversity loss by the year 2100, following land-use change and climate change. With the rapid development of industry and intensification of agriculture, the rates of nutrient inputs are expected to continue increasing in the future. The responses of terrestrial plant diversity to elevated mineral element inputs are of increasing global concern, especially with the globalization of atmospheric N deposition. However, information regarding the effect of mineral element input on terrestrial biodiversity is very limited in China. Based on available literature, we summarized the effect of nutrient element inputs on plant diversity in terrestrial ecosystems. The objective is to enhance our understanding about the effects of mineral element inputs on terrestrial biodiversity and to provide scientific base for sustainable ecosystem management. This review includes the following four aspects. (1) The concept of "limiting nutrient" and the coupling relationships between nutrient availability and plant diversity. Increase in productivity after nutrient addition is used as a common mode to determine if an individual or a community is limited by certain element. In general, nutrient enrichment changes the balance of elements in plants and affects their growth rate. The competition mechanism is commonly suggested to be responsible for the changes in biodiversity for the long term. Meanwhile, loss of diversity can affect mineral nutrient cycling by changing both nutrient absorption and release processes. (2) We summarized the results from the experimental studies about the effects of individual nutrient addition (especially for N, P, and K) or the combined nutrient addition on terrestrial plant diversity. Plant diversity generally declines in response to excessive nutrient inputs, depending on the quality and duration of nutrient inputs and on the ecosystem types. Compared to N, P availability may have stronger effect on the plant diversity, at least in some temperate regions. Mineral elements may also interact with some other factors such as CO₂ and further shape the responses in biodiversity. Lichens and mosses are suggested to be the most sensitive to external nutrient inputs, followed by herbaceous plants, shrub, and trees. (3) We discuss the mechanisms responsible for altering plant diversity induced by nutrient addition, at the ecosystem level and at the individual level. At the ecosystem level, competitive exclusion is widely accepted, because some fast-growing species become dominant in a plant community under nutrient enrichment. By decreasing the heterogeneity of soil nutrients, element inputs reduce the possibility of coexistence of different species. Soil acidification and subsequent aluminum toxicity are also suggested to decline plant diversity. In addition, nutrient enrichment can have indirect effects on local/regional plant diversity through promoting alien species invasion. At the individual level, elevated element inputs may lead to nutrient imbalance and increase sensitivity to biotic and abiotic stresses. The above mechanisms may also work together to cause species loss in the long term. (4) Lastly, we point out the limitations of the current research and present the potential research prospects in view of biodiversity protection and ecosystem management in the future.