限流耐旱树种木质部结构与耐旱性关系研究

Drought tolerance by restricting sap flow in the xylem is a new water-saving strategy for plants. The relationships between this strategy and xylem structures, hydraulic traits as well as ecophysiological characteristics need further research, which would improve the theory of drought resistance for plants and vegetation restoration. In this study, typical drought-tolerant tree species in the Loess Plateau will be selected as the materials and new equipment such as Cochard Cavitron Centrifuge, Low Pressure Flow Meter with multi-channels as well as Cryo-SEM will be used. First, vulnerability to cavitation of tree species with drought resistance by restricting sap flow in the xylem and those without restricting sap flow will be analyzed through comparative experiments. Meanwhile, xylem structures will be measured, which includes conduit wall thickness and ultrastructure of pit membrane.Moreover,variations and differences in xylem structures, hydraulic traits and physiological characters of each selected tree species cultured in soils at different water potentials will be investigated. The aim is to explore the strategy of the drought-tolerant tree species by restricting sap flow in the xylem in adapting to water shortage in soil from the xylem structures and hydraulic traits points of view, and to reveal the relationships between xylem ultrastructure and characteristics of the drought-tolerant tree species. Lastly, a new system of selecting and breeding drought-tolerant tree species would be formed. This would provide new theoretical evidences for selecting and breeding tree species best suitable for arid and semi-arid areas.

限流耐旱作为一种新的植物抗旱策略，其与木质部结构、水力特性及生理生态特征之间的关系亟待探究，这对完善植物抗旱理论，促进植被恢复意义重大。本研究拟选取黄土高原地区典型耐旱树种，采用全新的Cochard Cavitron离心机技术、多通道低压液流计技术、冷冻扫描电镜技术等，通过对比试验、测定分析限流耐旱树种与非限流耐旱树种栓塞脆弱性；木质部结构特征包括木质部导管壁厚度，纹孔膜超微结构等；不同土壤水势条件下木质部结构、水力特性及生理特征的适应性变化及差异。从木质部结构特征、水力特性上探究限流耐旱树种适应干旱土壤条件的策略。揭示限流耐旱树种木质部超微结构与耐旱能力的关系，建立全新的限流耐旱树种选育指标体系，为干旱半干旱地区适生树种的选育提供新的理论依据。

本项目按照研究计划主要进行了限流与非限流耐旱树种的栓塞脆弱性、木质部结构特征、水力特征，并且对其木质部抗空穴化能力及木质部结构对不同土壤水分适应性的研究，结果表明：6个耐旱树种木质部栓塞脆弱性大小为刺槐>白榆>沙棘>旱柳>元宝枫>榛木，限流耐旱树种与非限流耐旱树种栓塞脆弱性差异极显著(p<0.01)，所有树种的栓塞脆弱性曲线均可用单威布尔方程拟合，其中, 限流耐旱树种刺槐、沙棘和白榆的栓塞脆弱曲线为“r”型, 而非限流耐旱树种元宝枫、旱柳和榛木的栓塞脆弱曲线为“s”型。但沙棘和刺槐的脆弱性曲线用双威布尔方程也能更好的拟合，并发现沙棘的第二条威布尔曲线也许是由纤维相连的导管产生，提出“纤维桥假说”，认为纤维管胞既有助于导管间水分输导又有助于抵抗栓塞。刺槐脆弱曲线的探究实验发现离心机法建立的刺槐“r”型曲线并不能完全解释其水力特性，自然干燥法更适合测定其栓塞脆弱性。各树种栓塞脆弱性差异归因于木质部结构的差异，其中，木质部密度影响最大(t =0.702), 导管直径次之(t = 0.532), 导管长度影响最小(t = 0.010)，导管内径跨度、导管密度、导管连接度均能影响栓塞脆弱性。对杨属无性系的研究还发现纹孔膜面积也是影响栓塞脆弱性的主要因素之一。木质部水力特征与栓塞恢复能力的大小密切相关，特别是木质部栓塞脆弱性（P50）和水力直径大小与栓塞恢复能力有很强的相关性，是决定栓塞恢复能力的主要影响因子。对不同土壤水分条件的适应性研究发现相比于水分充足条件，干旱环境下生长的植物更不易栓塞，叶水势与净光合速率下降幅度小，抗旱性更强。另外，我们还比较了导管长度的两种测定方法，发现动态方法（空气注入法）测定平均导管长度比静态方法（硅胶注射法）测定的长。.通过本项目的研究，搞清了限流与非限流耐旱树种在栓塞脆弱性、木质部结构特征、水力特性上的差异，详细阐明了耐旱树种木质部解剖特征、水力特性、生理生态指标与耐旱性间的关系，丰富了选育耐旱树种的指标体系，为干旱、半干旱地区选育耐旱树种，恢复植被，保护环境，维持生态平衡提供了重要的理论指导。

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