科尔沁沙地主要防风固沙树种衰退死亡风险及其生理机制研究

The problem about widespread tree decline and mortality across many forests of the world in the context of climate warming has received increasing attention. The increasing drought stress caused by climate warming is considered to be an important cause of tree death in water-deficient areas, but the trend and mechanisms of tree decline and mortality resulted from drought are still unclear. Therefore, it is urgent to carry out relevant physiological and ecological researches under climate warming. This proposed project is planned to study the main windbreaks and sand-fixation tree species in Horqin Sandy Land, a key area for windbreaks and sand-fixation in northern China, relying on two ecological research stations of Institute of Applied Ecology, CAS. First, the differences of the adaptation of main tree species to dry environment will be identified by investigating the hydraulic architecture and related important functional traits. Then, the resistance and recovery of major tree species to extreme drought and their relationship with tree decline and death will be assessed using dendrochronological technique from a longer time scale. Last, the quantitative relationship between tree radial growth and climatic factors will be explored using simple correlation analysis. Based on the above analyses, the features and trends of main wind-proof and sand-fixing species responses to climate change will be predicted in the Horqin Sandy Land under the background of climate warming. The expected results of this project will provide theoretical and scientific basis for the selection of sand-fixing and afforestation tree species and the prevention and control of land desertification in water-deficient areas of northern China.

气候变暖背景下全球大范围内树木衰退死亡的问题受到了普遍关注，其中气候变暖带来的干旱胁迫加剧被认为是水分匮乏地区树木死亡的重要原因，但干旱导致树木衰退死亡发生的趋势以及相关机制仍不明确，亟需在气候变暖背景下开展相关生理生态学研究。本项目拟以我国北方防风固沙重点区域—科尔沁沙地的主要防风固沙树种为研究对象，依托我单位地处该区的生态研究站，通过树木水力结构及相关重要功能性状的测定分析，明确主要树种对干旱环境的适应性差异；采用树木年轮分析技术，从较长时间尺度评估主要树种对极端干旱的抵抗与恢复能力及其与树木衰退死亡间的关联；采用相关分析法，探讨树木径向生长与气候要素间的量化关系，预测气候变暖背景下科尔沁沙地防风固沙树种对气候变化的响应规律和趋势。该研究的预期成果将为我国北方水分受限区域生态建设与林业经营实践中固沙造林树种的选育、土地沙化防治等方面提供理论科学依据。

近几十年来全球范围内出现了广泛的树木衰退死亡现象，这种现象在水分受限区域尤为显著。与气候变化相关的干旱胁迫加剧被认为是造成树木死亡的重要原因，但干旱导致树木衰退死亡的发生趋势及相关机制仍不明确，迫切需要开展相关的生理生态学研究。本项目研究以我国北方防风固沙重点地区—科尔沁沙地及其附近的樟子松、油松和华北落叶松等主要防风固沙树种为研究对象，依托位于该区域的重要生态站，利用树木年轮和水力结构分析方法等关键技术手段，研究了这些树种的生长衰退风险及其水分生理机制。通过对科尔沁沙地水分条件不同的两个样地（章古台-半湿润区、乌兰熬都-半干旱区）樟子松和油松径向生长指标（如胸高断面积增量）的对比分析发现，与相对湿润的样地相比，更干旱的样地具有更明显的生长下降趋势和更大的衰退风险；树轮气候关系分析显示，更干旱样地的树轮生长对5-7月降水量和均温均更为敏感，表明树木生长衰退可能与温度上升导致的水分胁迫有关；此外，更干旱样地具有更低的水力导度（边材比导率和叶片比导率）和更高的导水功能丧失百分比，表明严重的水力限制可能是导致防风固沙树木衰退的重要生理机制。同一样地树种间的对比分析发现，樟子松相比油松具有更高的水力导度和径向生长速率，但更易遭受水分胁迫的不利影响。因此，在水分受限较严重的沙化区域，油松可能比樟子松具有更强的存活和防风固沙能力。通过对科尔沁沙地西南侧的塞罕坝地区最重要的防风固沙树种华北落叶松和樟子松沿海拔梯度的生长及水力特征的分析发现，在中、高海拔区前一树种具有更高的水力导度和径向生长速率（胸高断面积累积增量），但在较低海拔区更干旱的环境下后一树种具有更高的径向生长速率和更低的导水功能丧失百分比，表明在水分匮缺较严重的环境条件下后一树种可能更适合用于造林和防止土地沙化。该项目研究揭示了研究区主要防风固沙树种衰退死亡的生理机制，可为水分受限区域造林树种的选择和土地沙化防治提供科学参考。