多空间尺度热带山顶矮林植物功能性状分异及其对环境变化响应的研究

Tropical dwarf forest (TDF) is a most completely conserved forest in tropical regions, which harbors a unique biodiversity and special habitats. Trees in TDF are considered to be susceptible to environmental changes, and thus are characterized by unique ways adapting to these environments. Additionally, functional traits have been thought to objectively express plant adaptation to environments, and therefore, are regarded as effective indicators to environmental changes. In this study, we established the typical TDF plots with environmental gradients (e.g. air temperature, precipitation and soil factors) at different parts of Hainan Island, and measured functional traits for each individual tree in addition to environmental factors. We predicted that variation in tree functional traits in TDF at island scale would exhibit different patterns from those at local community scale, and impacts of environments on functional traits at island scale would show different patterns from those at local community scale. We tested our hypotheses according to the following two steps. Firstly, we examined variation in distribution for each trait at intraspecific level, interspecific level, community level and site level, as well as variation in phylogenetic signals for each functional trait at division level, order level, family level, genus level and species level, using a method of hierarchical variance partition. Then we compared the above variation in functional traits at the island scale with that at the local community scale, and assessed TDF plant strategies and their patterns. Secondly, we tested how the phylogeny and environments impacted on variation in functional traits both at the island and local community scales, using a general linear mixed model. Then we explored how the environments at different spatial scales impacted on functional traits by untangling the phylogenetic effects. Meanwhile, we examined the impacts of different environments on functional traits using a partial Mantel test, and assessed the mechanisms of tree response to environmental changes in TDF. This study can contribute to the developments of functional trait knowledge and their application to community ecology. The results and data will be helpful for the study on how the global changes influence on ecosystem structure and its functioning.

热带山顶矮林是热带地区保存最完整的一种森林类型，存在特有生物多样性和特殊生境；其植物对环境变化敏感，可能存在独特的适应环境方式。植物功能性状能客观表达植物对外部环境的适应性，是指示环境改变的有效工具。本研究在海南岛有环境梯度（如温度、降水和土壤因子）的热带山顶矮林分布区设置典型样地，通过基于个体水平的植物功能性状和环境因子测定，在本地群落和全岛尺度，分析功能性状在种内、种间、群落和样地水平的分布特征及其在门、目、科、属和种水平的系统发育信号强弱，探索不同空间尺度热带山顶矮林植物的适应策略及其变化规律；比较系统发育和环境因子对功能性状分异特征的影响，然后除开系统发育因素，探索不同空间尺度环境因子对功能性状的影响规律，阐明热带山顶矮林植物对环境变化的响应机理。项目能推动我国功能性状理论在群落生态学的应用，有助于探索全球变化对生态系统结构和功能的影响。

热带山顶矮林分布在海拔1200m以上的山顶，是保存最完整的一种森林类型。其物种多样性、环境特征及植物对环境的适应方式可能与低海拔热带森林不同。在海南岛霸王岭、尖峰岭、黎母山和五指山热带山顶矮林建立2.12 ha样地。测定了木材密度、比叶重、叶氮含量等13个植物功能性状；测定了植物DNA条形码，建立系统发育进化树；测定了空气温湿度、冠层开阔度、土壤有机质等9个环境因子。PCA分析表明，空气温度、土壤氮磷含量、林冠开阔度等因子是热带山顶矮林主要环境因子。以rbcL、matK、trnH-psbA和ITS为DNA条码构建系统发育树，发现rbcL，matK，trnH-psbA和ITS的PCR扩增成功率在50%以上，测序成功率分别为在45%以上，4个片段都有较好的通用性；ITS对热带山顶矮林的物种鉴别成功率最高（47.20%±6%），rbcL最低（41.50%±3%）；rbcL+matK+trnH-psbA组合能构建热带山顶矮林最优系统发育进化树。高度、叶面积、比叶重（LMA）、叶绿素含量（Chl）、叶片厚度（LTh）和木材密度间都显著正相关，回归斜率与1或-1都有显著差异，表现为异速生长关系。LMA-Chl和 LMA-LTh的回归斜率不随群落组织水平及样方大小变化，没有尺度依赖特征；相反，其它功能性状组合的回归斜率随群落组织水平及样方大小水平变化，有尺度依赖特征。系统分类水平上功能性状的分异主要表现在物种水平，而群落组织水平上功能性状的分异主要表现在种内和种间水平。分析热带山顶矮林物种在不同样方大小的共有度，发现不同多度及径级物种都呈现非随机聚集，且较大样方尺度的聚集度最大，反映植物空气低温和土壤低磷胁迫，物种间表现为促进关系。计算物种比叶面积和最大物种高度平均值的观测值与预期值间的效应大小，发现热带山顶矮林中比叶面积小和高度大的物种有生存优势，分别受由空气温度筛和光照的驱动。多元回归分析环境因子对植物功能性状的影响，发现热带山顶矮林土壤磷和氮影响植物功能性状分异。结合系统发育进化树检测物功能性状的系统发育信号，发现比叶重、木材密度、叶片氮磷比受系统发育显著影响；分析此三个功能性状的PIC值与环境因子关系，发现土壤全磷对比叶重有显著影响，土壤有机质、全磷、全氮对叶片氮磷比都有显著影响，全氮的影响较大。