严重侵蚀区干旱驱动马尾松水力输导障碍与碳饥饿研究

Hydraulic failure and carbon starvation hypotheses, among others, are suggested to explain the physiological mechanism underlying drought-induced plant mortality. In the hydraulic-carbon feedback loop that functions between these two mechanisms, transport and utilization of non-structural carbohydrates are critical for loop coupling. On the basis of previous studies, we plan to impose four different degrees of drought, by in situ experimental throughfall reduction, on P. massoniana, in serious soil erosion area in Changting of Fujian Province where drought stress and thus vulnerability of the ecosystem both exacerbate. By exploring the hydraulic failure and carbon starvation characteristics during the drought-induced plant mortality to determination of sap flow, hydraulic conductivity,photosynthesis and respiration rates. And we also look at the sources of non-structural carbohydrate,which is transported by the phloem.By measuring parameters relating to hydraulic failure and carbon starvation, and recording physical and chemical properties of soil, we aim to reveal the main drought-driven physiological mechanisms cotrolling the death of P. massoniana and look at the threshold value at which drought will cause P. massoniana to die. Our work will serve as direct reference to predict the future P. massoniana mortality in the event of extreme drought, and to provide more scientific information and help with respect to subtropical forest management under global climate change.

干旱胁迫驱动植物死亡的主要生理机制有水力输导障碍和碳饥饿，这两个生理机制间具有水力-碳反馈回路，非结构性化合物的运输和利用是耦合这条回路的关键环节。福建长汀严重土壤侵蚀区面临干旱胁迫加剧的威胁，森林生态系统脆弱性增加。在前期研究基础上，本项目拟以该地区森林生态系统的关键种-马尾松为研究对象，利用野外原位人工隔离降水技术，模拟4种干旱胁迫梯度下马尾松死亡的过程，通过测定树干液流、水力导度以及光合/呼吸速率研究马尾松水力输导障碍、碳饥饿的发生发展特征，通过稳定碳同位素技术，研究韧皮部运输的非结构性碳水化合物的来源。以上研究将揭示导致马尾松死亡时的干旱阈值；阐明干旱胁迫导致马尾松死亡的水力输导障碍和碳饥饿的耦合机制。研究结果可为解释干旱导致植物死亡的生理机制提供重要证据，为预测未来极端干旱事件发生时马尾松的死亡率提供直接参考，为制定亚热带森林应对气候变化的管理措施提供科学依据。

福建长汀严重土壤侵蚀区的生态环境脆弱，未来干旱可能威胁到这一地区植物的生存，本项目旨在研究干旱导致马尾松死亡的主要生理机制，我们发现马尾松具有很强的抗旱能力，在进行人工隔离降雨两年后才开始发现个别马尾松死亡，研究揭示了马尾松抵御干旱的主要机制有:降低叶片水势，从而增加和土壤的水势差，使其仍能维持连续的液流；通过夜间的水分流动补充生理活动所需的水分；将叶片的光合产物被更多地分配到枝条用于维持细胞间的渗透压平衡；以及更多地利用地下水和雾水。而在马尾松死亡时水分输导完全停止，而非结构性碳水化合物库并没有完全枯竭，碳饥饿致死也许并不是整个植株水平上发生的，而是某一组织或器官降低到一定的阈值后即发生渗透调节失效或其他一系列代谢原因而引起死亡。