植物功能性状与不同生活史阶段生长-存活权衡策略

The differentiation in the trade-off strategies of plants growth and survival between different tree species promotes the species coexistence in forest community. As quantitative indicators of life strategies, plants functional traits bridge the ecophysiological characters at species individual level and the structure and dynamics of forest community. Plants functional traits reflect the trade-off of plants strategies through the whole life history. Clarifying the relationships between plants functional traits and the plants strategies was the basic issue in exploring the effects of plants functional traits on the structure and dynamics of forest community. However, most previous studies focused on the relationships between plants functional traits and the plants strategies in a certain phase (e.g. adult tree), rather than the whole life history, resulting in partial conclusions. Additionally, community dynamics are controlled not only by plants functional traits, but also by environmental factors and density dependence. In this project, based on the 25 ha dynamic monitoring plot, we monitored the forest seed rain and the followed species survival and growth conditions of seedling, sapling and adult trees, measured a set of functional traits of plants in different phases of life history, collected the data of environmental factors, and aimed to (1) find out the key functional traits which controlled the plants survival and growth in different phases of plants life history; (2) clarify the effects of environmental factors and density dependence on the trade-off strategies of plants individual survival and growth; and (3) explore the key factors in determining the trade-off strategies of forest community, and further explain the mechanisms for community dynamics in subtropical forests. The project could help us to establish reliable relationships between plants functional traits and plants growth in different phases of life history, and could also provide new methods for calculating forest growth and carbon sink.

物种之间生长和存活权衡策略的不同促进森林树种的共存。植物功能生态学的发展将植物个体的生物学属性与群落动态结合起来。厘清功能性状如何影响植物个体采取的生态策略，是功能性状与群落动态关系研究的首要问题。在以往研究中，往往只关注了某一个生活史阶段，从而得到了片面的结果。而且，植物群落动态既取决于物种的功能性状，同时又受制于群落内的环境条件及密度制约效应。本项目基于八大公山25 ha动态监测样地种子雨数据以及幼苗、幼树、成树的生长、存活数据，物种的功能性状数据，结合环境因子，试图研究(1) 不同生活史阶段影响植物生长、存活的关键性状因子；(2)环境条件和密度制约效应对植物个体生长、存活权衡策略的影响；(3)寻找影响群落生长、存活权衡策略的关键因子，探讨亚热带山地森林群落动态和功能的机制。本项目的实施将会建立功能性状与植物生长的关系，可望为森林生长和碳汇计算提供新的方法。

物种的功能性状通过反映个体的建成、生长和存活等整个生活史策略来反映种群以及群落动态。厘清功能性状如何影响植物个体采取的生态策略，是功能性状与群落动态关系研究的首要问题。然而，以往的相关研究多局限于功能性状与大树的生长和存活的关系，发现功能性状对森林生长和存活的解释率极低。其可能的原因是某些功能性状只与生活史中某一阶段有显著关联，而在不同生活史阶段关系不明显甚至截然相反。同时，植物周围环境也会影响生长、存活的权衡策略。因此我们应该着眼于整个生活史周期来考察不同环境下功能性状和森林群落生长-存活权衡策略的关系。本研究关注了亚热带森林整个生活史周期的群落动态，找出每个阶段的限制因子，更加深入的了解森林群落的动态与植物功能性状的关系。通过本项目的实施，我们发现在植物生活史早期，不同功能群植物针对林下低光环境采取了不同生长适应策略，不同生长阶段幼苗也根据光环境的改变调整自身功能性状。八大公山常绿落叶阔叶林中的幼苗的生长主要受到氮素限制，且这种限制作用随着幼苗生长逐渐减弱。在小树阶段，仅有叶绿素含量与生长率显著相关。中树阶段，叶片干物质含量、叶片氮含量、磷含量显著相关。大树阶段，除比叶面积和叶绿素含量外，均呈显著相关。物种水平上仅磷含量与生长率存在显著相关。个体水平上生长率与叶片碳含量、干物质含量、叶绿素含量、磷含量、比叶面积、氮含量均存在极显著但微弱的相关。具有外生菌根的物种而言，生长被功能性状解释的程度更高，且其中性状对于生长变异的解释占比较多。该项目的实施整合了功能性状、环境因子和密度制约对群落动态的影响，拓展了生物多样性的研究内容；为结合植物功能性状、环境因子和密度制约来研究群落动态提供了可操作性的具体方案，建立了功能性状和植物生长的关系，为森林生长和碳汇计算提供了新的方法。