冬季栓塞抵抗和修复对长白山林区常见树种生产力和抗逆性影响的研究

In forest ecosystems of relatively high latitudes, freeze-thaw cycles frequently occur in the cold seasons and often induce xylem embolism in overwintering organs of trees, i.e. the blockage of water conducting conduits by air bubbles. Xylem embolism caused by freeze-thaw cycles can result in reduced hydraulic conductivity and even hydraulic failure and thus often cause tree damage, mortality or even large-scale forest decline in temperate regions. Keeping hydraulic integrity through enhancing winter embolism resistance or by an effective winter embolism repair process is critical to temperate forest tree species but the underlying mechanisms are still waiting for further investigations. For this proposed project, xylem hydraulics related to winter embolism resistance and repair will be investigated at the Forest Ecosystem Research Station of Changbai Mountain using a combination of three approaches, i.e. a common garden comparative study among dominant tree species, a intra-specific comparative study across the altitudinal gradient, and a seedling experiment under controlled light conditions. We have three major objectives for this project: 1) to clarify the structural and functional differences in traits related to hydraulic architecture and find out whether differences in the way of coping with winter embolism result in interspecific differences in productivity and stress tolerance; 2) to investigate the pattern of coordinated changes between structural growth and storage of non-structural carbohydrates along the environmental gradient where different risks of winter embolism are expected to occur; and 3) to investigate the mechanistic association between winter embolism refilling and non-structural carbohydrate storage and remobilization. Besides its own merits in tree physiological studies, this project will provide a sound scientific basis for improving practices in forestry, such as the selection of more suitable tree species for afforestation according to local environmental conditions, enhancement forest productivity, and dealing with the problem of natural regeneration failure for some founder species in natural forests of Northeast China.

在较高纬度地区树木越冬过程中频繁经历冻融交替，该过程可通过诱导木质部产生气穴化栓塞而严重威胁树木的水分传输安全，从而造成树木越冬伤害、死亡，甚至引发森林衰退等林业问题。在该环境中，越冬过程中木质部栓塞的抵抗力和修复作用对树木的存活和生长至关重要，但相关过程和机理仍不明确，亟需开展相关的树木生理研究。本项目拟依托长白山森林生态系统研究站，通过同质园测定、跨海拔梯度测定和幼苗实验，开展树木木质部冬季栓塞相关的抗逆生理研究。将明确该区主要造林树种的木质部水力结构差异，揭示水分传输效率和安全性对树木生产力和抗逆性的影响机制；探讨冬季栓塞风险随环境梯度发生变化时，光合产物在结构性生长和非结构性碳水化合物储存间分配的变化规律；揭示幼苗碳水化合物储存和再活化对冬季栓塞修复的影响机制。以期为该区造林树种选育、森林生产力提高、林下更新障碍解除等林业实践提供科学依据。

在较高纬度地区树木越冬过程中频繁经历冻融交替，该过程可通过诱导木质部产生气穴化栓塞而严重威胁树木的水分传输安全，从而造成树木越冬伤害，甚至引发森林衰退等问题。在该环境中，越冬过程中木质部栓塞的抵抗力和修复作用对树木的存活和生长至关重要，但相关过程和机理仍不明确。本项目以长白山具有不同栓塞抵抗和修复机制的优势阔叶树种为对象，主要从越冬水力安全角度分析了树木的相关功能性状和生理学过程，并分析了其对树木生产力和抗逆性的影响机制。获得了如下几方面的主要研究结果：1）在同质园条件下，冬季末树木组织可溶性糖含量与其栓塞修复力存在显著正相关，而与径向生长速率之间存在显著的负相关，揭示了冬季栓塞修复碳投入的种间差异及其介导的生长和水力安全之间的权衡机制。2）长白山不同树种木质部导管直径与其海拔分布上限呈显著负相关，高海拔分布上限的树种木质部特征更有利其抵抗冬季栓塞，揭示了水力功能性状决定树种海拔分布上限具有重要意义。3）发现环孔材和散孔材树种的早春物候差异和水力安全维持具有密切关联。由于环孔材树种水力系统对冻融交替高度敏感，早春寒潮的存在使其进化出较晚的物候以规避木质部栓塞风险。虽然环孔材树种发芽晚，但其具有更高的水力导度和叶片气体交换速率，在相对较短的活跃生长期内能够获得更大的碳收益，比散孔材树种具有更高的生产力，但其抗寒性相对较差，相对散孔材树种具有更低的海拔分布。本项目针对较高纬度地区冻融交替这一重要环境因素开展了树木水力结构研究，并取得了具有较高区域特色的创新性研究结果，特别是有关木质部正压对栓塞修复机制，以及树种的生产力和抗逆性与水力结构间的关联等的研究结果，对揭示较高纬度地区树木的抗逆生理机制和破解温带森林生产力形成的制约机制具有重要参考价值。