潮间带红树植物水力结构和功能及其与气孔调控行为的关系

Coastal mangrove forests have important ecological roles and economic value. They grow on extreme harsh habitats of tropical and subtropical intertidal zones, with high salt concentrations in the soil and sea water, anoxia in soil, high transpiration demand because of high temperature and irradiance and strong wind. Therefore, their xylems are subjected to high tension so that can be easily suffered from embolism and consequently hydraulic dysfunction. Our preliminary studies have shown some mangrove species have high xylem embolism resistance and some species are able to photosynthesize at rather lower water potential. It is unclear that how mangrove plants manage to transport water safely through the optimal hydraulic design and regulation of canopy transpiration. This project focuses on the hydraulic structure and stomatal regulation behavior of main Chinese mangrove tree species with different salt management mechanisms (salt exclusion, salt exclusion plus salt secretion, and semi-mangrove species). We will measure the anatomical and hydraulic characteristics of branch stems and leaves, canopy stem sap flow, photosynthetic gas exchange and ABA concentration of canopy leaves, water potential of plants, and environmental variables. We will also measure some terrestrial species of Rhizophoraceae for comparison. The objectives of this project are: (1) to characterize hydraulic structure and function in stems and leaves of main Chinese mangrove tree species with different salt management mechanisms; (2) to clarify stomatal regulation behavior of the main mangrove species; (3) to clarify the relationship between the vulnerability to embolism and stomatal regulation behavior and salt tolerance. The findings of this project will provide novel understanding on the mechanisms of mangrove trees in adaptation to the extreme intertidal harsh habitats, and provide important references for the conservation and sustainable utilization of biodiversity resources of mangrove forests, and for predicting their response to environmental change.

海滨红树林具有重要生态功能和经济价值，生长在土壤和水分盐分高、缺氧，蒸腾压力大的热带亚热带潮间带极端生境。因此，红树运输组织水分张力大，可能易发生气栓，使水分运输受阻。我们初步研究表明红树抗气穴能力很强，有些种能在低植物水势情况下维持较高的光合作用。红树植物如何通过水分运输系统优化设计和冠层蒸腾的调控解决水分运输的安全性仍是不解科学之谜。本项目以红树植物水力结构和气孔调节行为为主线，测定我国主要的具有不同盐分管理机制（排盐，排盐加泌盐，半红树）的红树植物木质部和叶片解剖结构和水力学功能，树冠液流、叶片光合气体交换、叶片脱落酸含量、植物水势、和环境因子。与红树科陆生种做比较。揭示红树植物枝条木质部和叶片解剖结构特点及其与水力学功能的关联；阐明红树植物气孔的调节行为，及其与耐气穴化能力、耐盐性的关系。为红树植物对极端生境的适应机制提供新认识，为红树林生物多样性资源的保护和持续利用提供科学依据。

生长在遭受盐分多重胁迫条件下，红树植物如何维持水分运输和利用安全，水分运输系统与叶片生理功能协同关系尚未研究过。按计划项目开展了下列研究：广西、海南15种红树木质部水力结构和功能，包含根系拒盐、叶片排盐树种，正红树和半红树；16种红树植物叶片解剖结构和生理功能特征；6种红树连续2年的树干液流测定；9种红树的气孔调节行为；12种红树植物叶片和细根的耐失水特性。在计划书之外，还增加了下列测定：红树养分计量学特征；不同种源红树幼苗对高温和低温胁迫的生理响应；菲律宾萨兰加尼湾典型红树的水力性状和叶片功能；澳大利亚两个广布红树种沿纬度梯度水力学特征的表型差异。项目阐明红树普遍具有小导管，水分运输效率较低，而抗栓塞化能力特别强。同时具有根系拒盐和叶片排盐的红树受盐胁迫较轻，植物水势较高，导水率较高，而抗栓塞能力稍弱。在北热带地区，红树水分运输效率与安全性呈权衡关系，而低纬度红树没有此权衡关系。红树林水分蒸腾消耗量在热带森林低值范围。红树叶片具有肉质性特点，较厚，较普遍具有储水组织，叶片耐失水能力强。大部分种气孔分布在叶下表皮，部分种为等面叶。红树叶脉密度较低，而光合能力较强。它们气孔调节行为可分为等水势、变水势行为和中间类型，气孔开度受植物水力特征和叶片脱落酸含量、光强、大气饱和水汽亏调控。红树细根耐失水，且有储水功能。红树叶片富集Ｐ、Ｃa、Ｍg、Ｎa、Ｓ元素，但是，缺N、Fe、Ｓi、Ｚn。叶片中的核酸磷、有机磷对于红树适应低温冷害起重要作用，叶黄素循环对于红树抗高温胁迫起重要作用，耐热性与耐冷性存在权衡。随生长地点温度升高，红树导管增大，提高导水效率，适应高蒸腾的要求，同时水分运输安全性增强。项目揭示红树植物具有特殊生理结构和功能和适应策略，其适应多重胁迫生理和分子机制值得进一步研究。研究结果对于红树林的保护、利用、生态修复以及认识其对全球环境变化的响应有重要参考意义。