红壤丘陵区人工针叶林植物水分利用及其对间伐的响应机制

Thinning is a potential forest management to increase the drought tolerance of the coniferous plantation in red soil hilly region. However, thinning will improve the understory growth, increase the competitive interaction of water sources among different life forms, and thus weaken the effectiveness of thinning on the improvement of tree drought tolerance. Understanding the interspecific differences in water-use strategy and clarifying the responses of overstory transpiration and understory evapotranspiration (ET) to thinning are crucial to optimize the ecosystem ET allocation. This project will study the anatomical features, morphological plasticity, and physiology properties of the root-stem-leaf water transport channel during wetting and drying processes. Combined with the stable isotope method and sap flow measurements, we explore the water-use strategy (e.g., drought-adaption strategy, water sources, and water-use efficiency) of dominant plant species and their responses to thinning of a coniferous plantation in red soil hilly region. Two water flux observation sites will be employed to study the genuine effects of thinning on the ecosystem ET. Combined with the studies of soil water dynamics and the interspecific differences of water-use strategy, we will illustrate the mechanism of thinning effects on the ecosystem ET allocation. The shrubs, with different water sources from trees, high drought tolerance and water-use efficiency, will be identified and should be maintained after thinning. The findings will have important implications in optimizing the ET allocation after thinning and improving the effectiveness of thinning on the improvement of tree stability against drought events.

间伐是缓解红壤丘陵区人工针叶林季节性干旱胁迫的重要措施，但也会促进林下植被生长。乔木与林下植被的水源竞争会削弱间伐对保留木水分胁迫的缓解作用。明晰间伐后植物种间水分利用的异同，揭示乔木蒸腾和林下蒸散对间伐的响应机制，是优化间伐后生态系统耗水分配的理论基础。本项目研究土壤干湿交替过程中植物根-茎-叶水分传输通道的解剖特征、形态可塑性和生理属性，结合碳、氢、氧稳定同位素法和茎干液流法等，探讨亚热带人工针叶林优势乔灌水分利用(对干旱的适应策略、水分来源和水分利用效率)的种间差异及其对间伐的响应机制；用双通量塔观测法研究生态系统蒸散，结合乔木蒸腾、土壤水分动态和植物水分利用种间差异，阐明亚热带人工针叶林生态系统耗水分配对间伐的响应机制；筛选间伐后被动耐旱、水分来源与乔木差异大、水分利用效率高的林下灌木。研究结果对优化间伐后生态系统耗水分配格局、提升间伐对林木干旱胁迫的缓解效应具有重要的指导意义。

间伐在缓解红壤丘陵区季节性干旱对林木胁迫的同时，也会激发林下植被生长。林下植被与乔木间的水分竞争会削弱间伐对保留木水分胁迫的缓解作用。明晰间伐后乔灌植物水分利用及干旱适应策略的种间差异，是优化间伐后生态系统耗水分配的理论基础。本项目依托40ha的针叶林间伐试验平台，基于植物根系形态与分布，水分来源及其季节动态，水力学运输和存储，叶片水势、光合等多器官属性测定，开展了整株植物干旱适应性的方法、机理与应用研究。明晰了间伐后林下植物与保留木间的水分竞争机制；明确深层水分利用能力是研究区植物干旱适应性的关键根系属性，指明植物水力学存储和碳存储是权衡关系，发现整株植物干旱适应性与经济谱的联系，揭示了植物避旱性与生长策略的协同关系。基于上述理论成果，识别了间伐后与保留木水分竞争大的林下灌木物种。研究结果对科学开展林下植被管理，优化间伐后生态系统耗水分配格局，提升研究区人工林生态系统质量具有重要的指导意义。 本研究回答了整株植物干旱适应性研究长期未解决的关键科学问题，相关研究成果发表在New Phytologist, Tree Physiology和Agricultural Forest Meterology 等主流期刊上，包括1篇New Phytologist（IF=8.512）亮点文章，1篇美国ESI数据库高被引论文，在国际上取得重要影响。