过去和现在气候条件下东南亚地区松属稀树草原和森林的生物地理和生物多样性研究

Pine stands of Pinus kesiya and Pinus merkusii occur as isolated patches across Southeast Asia, from China to Indonesia. They are found growing in both savannas and forests. Both pine species appear to require fire for natural regeneration, and they possess the juvenile grassy stage, an adaptation for coping with frequent fire. In forest stands there is little evidence of juvenile pine recruitment. Together this information suggests that at least part of the Pine savanna area is old, while the closed-canopy forests are a temporary successional stage. Pine savannas in other parts of the world support high herb diversity, but herbaceous diversity in Asia is poorly understood and more research is needed. The two pine species have different distributions, suggesting their ecological niches are different, but no comparative study has yet been attempted. Pine stands occur at higher, cooler elevations, indicating that they are relicts of more extensive distributions during the last glacial period. Pollen records support this. The genetic structure and diversity of these species provides a historical record of their advance across the region and their subsequent retraction after the Pleistocene. Environmental change in the Anthropocene will impact some biomes more severely than others. SE Asian pine savannas consist of C3 woody plants and C4 grasses, and are threatened by increases in both rainfall and atmospheric CO2 levels that will tilt the competitive balance in favor of C3 trees, and hence shift savannas towards forests. Understanding how future climates might affect these communities is essential for devising mitigation strategies to protect them.In this project, we aim to compare these two pine species and their associated savanna and forest communities across their geographical ranges in Southeast Asia. We will use genetic analyses to understand how their populations expanded and contracted in the past, and their capacity for climatic adaptation. We will measure their floristic and functional diversity to identify drivers and assess differences between the two Pinus communities and between savanna and forest vegetation types. These analyses will then help parameterize species distribution models and dynamic global vegetation models to predict future changes to the distribution of savannas and test possible management strategies. These assessments will inform conservation priorities and management needs in Southeast Asia.

思茅松和南亚松利用火来进行自然更新，其生态位不同，但在东南亚稀树草原和森林生态系统中都有分布，我们在森林中没有发现其幼苗，因此与热带稀树草原相比，郁闭林只是暂时的演替阶段。因为稀树草原生态系统的独特性，东南亚松属稀树草原具有重要要的生物多样性保护价值。由于全球变化，降水和二氧化碳浓度的增加使得C3树木更利于生长，因此稀树草原生态系统可能向森林转变，故了解未来气候对这些群落的影响对保护这一特有的生态群落至关重要。本项目将比较研究东南亚地区这两种松属植物为代表的稀树草原和森林的群落结构，利用遗传分析来探索这两种松属物种的种群扩散和回缩的历史以及对气候的适应能力，从而建立参数化的物种分布模型和全球动态植被模型，预测稀树草原的未来分布，为东南亚地区生态系统管理和保护提供意见。

本项目聚焦思茅松（Pinus kesiya）和苏门答腊松（P. merkusii）两种热带松属植物的种群历史及其周围的植物群落多样性，以及这两种树种及其所在的稀树草原群落在气候变化影响下的未来走势。项目的大部分工作原计划在东南亚进行，但由于新冠肺炎疫情持续了三年，占用了项目的主要时间，而位于东南亚的各国都实施了旅行限制，导致我们无法进行大量的实地调查。尽管如此，我们还是对云南省内的思茅松及其近源种云南松（P. yunnanensis）进行了谱系地理分析，并且将生物多样性分析转移到不同冠层覆盖度下云南松林地植物群落的差异，同时通过分别使用SDM和DGVM模拟了这三种松树及其所在的稀树草原植被分布的未来景象。..主要结果：.1.通过谱系地理分析，我们发现云南松种群间存在着大量的基因流，而思茅松则表现出强烈的种群结构，与其在东南亚的间断分布相呼应。两种松在云南南部的一个杂交区显示出二者线粒体基因流的不对称渗入。同时，我们分别在云南松和思茅松种群中鉴定出40个（占200,37个SNPs的0.2%）和1538个可能受到选择的SNPs（7.7%），所观察到的基因组变异与年平均气温和温度季节性的关系最为密切。..2. 我们分析了云南六个地点54个样地的地层植物多样性。草本植物多样性以喜光的C4植物为主；因此，从开放的稀树草原变为郁闭的森林，草地覆盖率和生物量都将减少。大量的形态种出现在以草本植物为主的地块，表明了在松林中保持开放景观的必要性。..3. SDM分析表明，思茅松和苏门答腊松在末次冰期占据了东南亚的大部分地区，此后在全新世期间他们的存在范围有所缩小。对未来分布的预测表明，这两种东南亚松树的生存空间范围将继续缩小，一些种群将面临灭绝。..4..使用DGVM对东南亚地区稀树草原与森林之间的动态变化分析表明，大气CO2浓度的增加将导致稀树草原的面积大幅下降，但林火可以使干热草原处于开放状态，防止其向森林转换。

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