新疆荒漠区树木的干旱死亡机制

Drought-induced plant mortality is a particularly prominent problem in arid desert regions under the background of global change, but the mechanism of drought-induced plant mortality in arid desert areas remains unclear. Ebinur Lake area plays important roles in ecological maintenance and stability of the north China due to it belonging to the one of Chinese sand storm source areas. However, the unreasonable use of water in the middle reaches causes the reductions in lake area and the local groundwater level, and subsequent to eliminate millions of hectares of local desert forest in recent years. In this project, the community samples will be firstly set up in Ebinur Lake area. Then species composition and quantitative characters of the plant communities, soil moisture content and the underground water level will be investigated. Additionally, based on community characteristics, soil moisture content and the underground water level, the community samples will be classified into different drought tolerance community types. Within each species of each community sample, the hydraulic traits and nonstructural carbohydrate, and an iso- to anisohydric continuum of stomatal regulation would be measured and established, respectively, in order to explore the different mechanisms of drought-induced plant mortality among communities, among life form, as well as between the individual developmental stages. Our project results are advantageous to improve the theoretical level of plant physiology, and to reveal the interactional mechanism of hydraulic failure and carbon starvation. Our results also play the major roles in desert forest protection and management in arid desert regions.

全球气温升高背景下，干旱引起树木死亡现象在荒漠区尤为突出，但当前死亡机制不明。新疆艾比湖流域作为我国沙尘起源地之一，生态作用巨大。然而，近年当地不合理水利用使湖面退缩和地下水位下降后，植物可利用水量减小，干旱胁迫加剧，造成大片荒漠森林死亡。但目前没有成果关注这一现象。本项目拟在艾比湖流域的自然保护区内设置样地，在调查土壤含水量、地下水位和群落数量特征的基础上，将样地归成不同干旱程度的群落类型。之后，测量每样地内每木本物种的水力性状和非结构性碳量，建立等水-非等水植物的水力性状和非结构性碳的变化谱，试图揭示艾比湖流域不同的群落间、生活型间、以及个体发育阶段上的树木干旱死亡机制。本项目成果，对揭示水力失衡和碳饥饿两种死亡机制在干旱荒漠区的交互作用、丰富植物生理学理论、保育和管理干旱区荒漠森林生态系统等，都具有十分重要的现实和理论意义。

本项目在新疆艾比湖国家湿地自然保护区的东大桥管护站附近，垂直于阿奇克苏河从河岸至沙漠设置了非干旱、轻度、中度和严重干旱4个水分梯度，之后利用土壤含水量和地下水位验证梯度；随后，测定了系列水力结构、水力性状和碳代谢特征等，分析干旱引起树木死亡机制在干旱梯度上的变化。本项目发现：1. 干旱梯度上群落内木本植物的水力性状和非结构性碳存在显著差异，水分调节策略也存在不同；2. 不同木本植物生活型以及木本植物发育过程中功能性状显著不同，面对干旱胁迫时采用不同的策略；3. 干旱引起乔木的死亡率显著高于灌木；4. 小树的死亡率显著高于大树；5. 相对灌木，乔木具有更多元化的水力策略以应对干旱胁迫；6. 当地的乔木种胡杨在个体发育中，干旱死亡机制从水力失败逐渐向碳饥饿转移。综上可知，不同木本植物面对干旱胁迫时其水分调节策略存在差异；干旱环境中，乔木主要受到干旱胁迫的影响，灌木处了干旱胁迫外，还面临着其它环境胁迫；木本植物发育前中期不仅要面对干旱胁迫还受到自身发育的影响，发育后期主要受到干旱胁迫的影响。本研究成果，对于揭示干旱荒漠区中木本植物水分调节策略、丰富植物生理学理论、保育和管理干旱区荒漠森林生态系统等，都具有十分重要的现实和理论意义。