不同热带云雾林分布区植物群落构建机制：基于系统发育及功能性状研究

Assessing the ecological processes underlying the community assembly is vitally important for us to understand the community structures and ecosystem stability. The typical tropical cloud forest (TCF) in Hainan Island is tropical montane dwarf forest. Trees in these forests are deformed, elfin and covered in epiphytes. Environmental conditions are characterized by low air temperature, strong winds, frequent fog and relatively high levels of ultraviolet radiation compared with low altitudinal tropical forests. Community assembly processes in TCF, such as environmental filterings and biotic interactions, are assumed to be different from the low-altitude tropical forests. In this study, we will establish dynamic plots in 5 TCF distribution areas in Hainan Island, with environmental gradients such as air temperature, precipitation and soil conditions. We will survey plant species diversity and measure functional traits for all individual plants and species, as well as measuring DNA barcode information for all species, and environmental factors. We predict (1) that the community membership both within and among the 5 TCFs would significantly differ related to ecological strategies and phylogenetic relatedness; and (2) that within- and among-TCF community would be organized with different ecological processes according to patterns of trait dispersion, functional and phylogenetic similarity, and that these processes would change with spatial scales and environments. We will test our hypotheses according to the following steps. First, we will create phylogenetic trees for each and overall 5 TCFs, using DNA barcode information. After identifying plant response traits and effect traits, and assessing the phylogenetic signs for each functional trait, we will explore the membership of plant species by testing both within- and among-TCF patterns of intraspecific and interspecific variation in functional traits, as well as testing patterns of functional diversity and phylogenetic diversity after partitioning them into alpha and beta components. Second, we will examine how the environments affect plant species’ ecological strategies and evolutional relatedness by testing the relationships between environmental factors and functional traits, functional diversity and phylogenetic diversity. Third, we will examine the within- and among-TCF assemblages by testing trait dispersion at the intraspecific and interspecific levels, and functional and phylogenetic similarity, using null models. Finally, we will assess the scale-dependence/independence of community assembly processes and how these processes change with environmental gradients by testing the relationships between trait dispersion, functional and phylogenetic similarity and environmental factors at different fine spatial scales, using mixed-effects models. This study will help us understand the plant species distribution in TCFs from multiple functional trait axes and evolutional relatedness. The Results are expected to improve our knowledge on the scale-dependent/independent mechanisms of the high altitudinal tropical forest community assemblage and their patterns with environment changes, and thus will enrich the theory of tropical forest community ecology, and will be helpful for the forest biodiversity conservation and forest managements.

热带云雾林通常分布在海拔1300 m以上的山顶或山脊，存在特殊生境和特有生物多样性，其群落构建机制可能与低海拔热带林不同。本项目拟在海南岛有环境梯度的5个不同的热带云雾林分布区建立固定样地，测定植物功能性状、DNA条形码信息及环境因子。通过构建系统发育进化树和分析功能性状的谱系信号，比较不同面积大小的群落内部及群落间功能性状、功能多样性及谱系多样性，分析它们与环境因子的关系，探究不同群落中物种的生态策略及谱系关系变化规律；分析不同面积大小群落中种内水平及种间水平功能性状的趋同/趋异性、功能相似性及谱系相似性变化及其与环境因子的关系，辨识作用于每个群落构建的生态过程类型，比较影响不同群落构建的生态过程异同，探究这些过程随空间尺度及环境梯度的变化规律。项目有望揭示高海拔热带森林群落结构的功能性状及进化基础，阐明物种多样性维持机制，有助于丰富热带林群落生态学理论和森林植物多样性的保育。

探究森林群落的构建机制是生态学研究的热点。由于生境及物种组成的特殊性，位于热带地区高海拔山顶和山脊的热带云雾林具有独特的群落构建机制。项目以海南热带云雾林为研究对象，调查了群落的物种组成（累计调查20402株），收集了7个环境因子、18项功能性状和1690条DNA片段等数据，构建了云雾林群落系统发育树并检测了性状的系统发育信号，分析了群落的谱系结构、植物功能性状及其多样性特征并识别了对群落特征起主要影响的环境因子，揭示了群落的构建机制及其变化规律。结果显示，基于rbcL + matK + trnH-psbA组合所构建的系统发育树支持率最高，trnH-psbA片段的PCR扩增成功率和测序成功率最高，ITS片段的物种鉴定成功率最高。植物功能性状的系统发育信号大多不显著，表明植物的谱系生态位保守性低。霸王岭云雾林群落的谱系多样性高于黎母山和尖峰岭云雾林群落，它们分别具有最高的功能丰富度、功能均匀度和RaoQ功能多样性指数。相比物种多样性与谱系多样性，功能多样性与地上生物量的关联性更强。植物木材密度的变化主要来源于种间，叶性状变化的种内与种间来源比例相似。植物叶片氮磷比大于17，表明植物普遍面临低磷胁迫。基于功能性状的主成分分析表明植物在资源获取型与资源保守型策略之间存在权衡。株高、比叶重和木材密度两两之间的标准化主轴回归斜率在个体、物种和群落水平之间无显著差异，表明植物普遍存在异速生长的特性。土壤磷素对群落谱系结构、功能多样性和植物的生态权衡具有显著影响, 是影响群落构建的关键环境因素。植物的性状特征和谱系关系在不同的物种库、空间尺度和分布区均呈聚集格局，说明环境筛选是群落构建的驱动过程。该过程在较大的物种库和较小的尺度上更明显；黎母山和霸王岭的环境筛选程度分别因坡度和土壤磷含量而异。基于种内性状变异的进一步研究表明植物的生态适应能力具有很强的可塑性。研究成果有助于解密海南高海拔热带森林群落的物种共存与多样性维持机制，对森林生物多样性保育和生态系统管理具有指导意义。