热带丛生竹种适应季节性干旱的生理生态机制

Bamboos play an important role in social economy and ecosystems. Most clumping bamboo species are shallow-rooted, highly sensitive to the changes of water and temperature, and mainly distributed in tropical areas. However, the climate in most of their growth and distribution regions changes seasonally, with a long and distinct dry season. As monocotyledonous perennial plants, bamboos lack vascular cambium, so the cavitated vessels induced by drought could not be replaced by developing new water conducting tissues. Therefore, under drought stress, it is particularly important for bamboos to maintain normal physiological functions by improving their resistance to xylem embolism or the capability of refilling the cavitated vessels. However, little is known about the eco-physiological mechanisms of how tropical clumping bamboos adapt to seasonal drought. In the present study, we will select five common tropical clumping bamboo species in a tropical seasonal rain forest in Xishuangbanna, Yunnan Province. The seasonal changes of hydraulic conductivity, leaf water status, leaf osmotic adjustment and root pressure will be monitored. Leaf and branch xylem vulnerability to cavitation induced by drought, their vessels anatomical characteristics and pit structural features will also be investigated. The knowledge of this study is important for us to understand the effect of seasonal drought on water transport and leaf gas exchange of tropical clumping bamboos, the roles of osmotic adjustment and root pressure in keeping their physiological functions, and the relationship between the resistance to xylem embolism and the anatomical structure of their vessels. The investigation on how tropical clumping bamboos adapt to seasonal drought will provide a scientific basis for the protection and utilization of bamboo species.

竹子在社会经济和生态系统中具有重要作用。竹类植物中的丛生竹种根系较浅，对水热条件敏感，且主要分布于热带地区。然而，在其生长和分布的大部分区域，气候季节性明显，干季时间较长。作为单子叶多年生植物，竹子无形成层，不能通过形成新的水分输导组织替代干旱引起的气穴化导管，因此提高木质部栓塞抗性或有效修复气穴化导管对其干旱胁迫下生理功能的维持尤为重要，但目前对热带丛生竹种适应季节性干旱的机制知之甚少。本研究拟对西双版纳地区常见的五种热带丛生竹水分传导、叶片水分状况、叶片渗透调节及根压的季节动态变化进行研究，了解季节性干旱对热带丛生竹水分运输和气体交换的影响，揭示渗透调节和根压对干旱胁迫下其生理功能维持的作用，结合竹子木质部栓塞脆弱性和导管及导管壁上纹孔结构特征，探讨热带丛生竹导管抗气穴化能力与其解剖结构的内在关系。本项目将阐明热带丛生竹适应季节性干旱的生理生态机制，为竹类植物的保护与利用提供科学依据。

竹子在社会经济和生态系统中具有重要作用。竹类植物中的丛生竹种根系较浅，对水热条件敏感，且主要分布于热带地区。然而，在其生长和分布的大部分区域，气候季节性明显，干季时间较长。作为单子叶多年生植物，竹子无形成层，不能通过形成新的水分输导组织替代干旱引起的气穴化导管，因此提高木质部栓塞抗性或有效修复气穴化导管对其干旱胁迫下生理功能的维持尤为重要，但目前对热带丛生竹种适应季节性干旱的机制知之甚少。本项目以黄金间碧竹为实验材料，通过使用热消散探针的方法，监测了其茎秆的液流（Fd），并分析了白天的和夜间的Fd在旱季和雨季的动态变化。此外，同步监测了这种木本竹子的根压、茎秆周长（直径）及气孔导度（gs）的日间变化。研究结果发现：（1）无论是在旱季还是雨季，白天的竹子茎秆液流（Fd）对饱和蒸汽压差（VPD）的响应呈现出以指数方式增加，并且当VPD开始增加时，Fd则呈现出快速的初始增长。在上午时段，当光强和VPD增加时， Fd和gs也都开始快速增加，但是一旦达到它们的最大值后就开始大幅下降。相比于生长在同一研究地点的几种具有代表性的树木和棕榈，竹子白天的Fd对VPD的响应更快速，这表明竹子茎秆液流和气孔对周围环境气象因子变化有较快反应。（2）在竹子茎秆较高和较低部位，上午时段的Fd几乎是同时开始增加，然而在下午时段，相比于茎秆较低位置的Fd，茎秆较高位置的Fd则要较高。与此相一致的是下午时段的茎秆周长表现出明显降低。不同于一般树木，竹子的茎秆储存水并没有被用于上午时段的蒸腾，而是被用于下午时段，并且竹子的夜间液流与其根压几乎同步发生。本项目揭示了竹子通过较快的茎秆液流和气孔调节来应对光强和蒸腾的需求，同时茎秆中的储存水被用于下午时段的蒸腾，而根压似乎是对竹子茎秆储存水在夜间再补充的一种机制。本项目阐明了热带丛生竹适应季节性干旱的生理生态机制，也为竹类植物的保护与利用提供科学依据。