亚热带森林植物高生长对策与物种共存机制

Plant height reflects the ability of light capture for securing carbon profits, is one of the most important functional traits in plant ecology. It is common to find many plant species with close stand stature can coexist within a forest community, and even the same niche, suggesting plant maximum height can't fully reflect their competitiveness. Therefore we think the different height growth process (height growth trajectory) may interpret the intrinsic mechanism of species coexistence in a community, analyzing the costs and benefits of different plant height growth strategies will open a breakthrough to explain the formation of species coexistence. Three typical forest communities (with three dominant families as Fagaceae, Lauraceae, Theaceae) of evergreen broad-leaved forests located in southwest China is to be selected in this research project. The height growth trajectory with time will be monitored for all seedlings and saplings of all woody species (mainly of sun and shade-tolerant of shrubs and trees) in the community. Their related branching manners, architecture properties and some important tree traits will be studied at both plant and twig scales along with plant ontogeny. The relationships between the pace of height increasement and important leaf and stem morphological, anatomical and eco-physiological traits will be studied. Height growth strategies of different species with apparent different light-capture properties will be categorized. The quantization of boundary effects of the benefit and cost analysis for the twigs in sun and shade positions are expected to link the strategy combinations among isolate strategy of height growth as well as leaf and twig traits, together with community phylogeny. Consequently, the integrations of above work are on understanding of species coexistence, community dynamics and diversity maintenance of the forest community.

高度与植物对光资源的竞争能力密切相关，是植物最重要的功能属性之一。森林植物有很多物种的高度非常接近，却都能共存于同一个群落之中，甚至是同一个小生境中，表明植物的最终高度并不能完全反映植物的竞争能力。我们认为物种间不同的高生长节律，即高生长的过程（轨迹）的差异，应该是森林群落物种共存的一个重要机制，探索植物不同高生长对策的成本与收益将可能为解释这一机制的形成打开突破口。本项目拟以亚热带三种典型森林群落（壳斗科、樟科、山茶科植物为建群种）为研究对象，观测林中木本物种（主要是阳生和耐荫灌木和乔木物种）的幼苗或幼树的树高、分枝和构型对策，并通过对建群种不同光位置小枝尺度上的形态、生理生态相关功能属性的研究，描绘高生长的节律，量化不同光策略的植物高生长的边际成本与收益，分析不同物种与光竞争和利用策略相关的高生长对策类型，并解析其与群落系统发育的关系，从而阐释森林群落中物种共存和生物多样性维持机制。

按照项目任务完成了对亚热带常绿阔叶林3个典型群落70多种植物共2000多棵植株连续4年每月1次的树高生长监测，并对常绿阔叶林下代表性的物种进行了叶-茎功能属性的动态研究，结合林内光资源分布与物种在群落中的地位之间的关系进行了深入分析，主要研究进展和成果为：1）树高生长具有显著的季节动态，通过对林下物种按照阳生木本植物（落叶物种、部分常绿灌木或小乔木物种）、耐荫木本植物（大多灌木）、冠层乔木物种幼苗-幼树阶段的几种生活型物种进行高生长对策的描述，以及对所有个体生长动态数据的分析表明，春季的生长量占全年总生长量的75.0%，夏天为13.9%，秋季8.3%，冬季为2.8%。其中又以4月和5月生长量最高，不同生活型、生长型以及处于不同群落地位的物种之间树高生长季节性节律差异显著。常绿植物的月均生长量较落叶植物高；阳生木本植物70%以上的生长量在春季完成，一些耐阴灌木在夏秋季生长全年25%以上的生长量，部分物种在冬季的生长量达到20%。因此归纳出四种不同的树高生长模式：春季抽生模式、春夏抽生模式、缓慢生长模式、冬春抽生模式。2）在个体发育尺度上，树高的生长率与初始标记树高具有显著的正相关关系，而不同高度的幼树自疏（死亡）高峰发生在10-20cm与90-100cm，2月和7月是其死亡高峰期，揭示个体发育尺度上树高生长、存活与光资源有效性以及限制光资源条件下植物个体碳收支平衡的关系；3）通过对典型物种与光资源获取相关的叶-茎功能属性关系研究显示，不同生活型和耐荫性物种的光合、生物量分配与营养含量分配等对策的生理生态机理，揭示了常绿阔叶林林下物种的多样性共存现状与其潜在机制。