胡杨水分再分配对荒漠杜加依林植物多样性的影响

The hydraulic redistribution (HR) of deep-rooted plants have significantly changes the pattern of water distribution in arid deserts, which subsequently induce the shallow-rooted shrubs and herbs assembly in redistribution area and maintain the biodiversity in arid deserts. Our previous research revealed that the constructive species i.e., Populus euphratica of Tugai Forest, has HR, and that total amount of HR significantly correlated with species richness and abundance, but none of those studies have directly tested this mechanism through experiment. In addition, shallow-rooted herbs and shrubs that assembled in HR area have improved the nutrient contents because of the effects of the “fertile island” and “crown interception”. Thus, these processes contributed a positive feedback of water and nutrient among deep- and shallow-rooted plants. However, the above complementarity relationships between deep- and shallow-rooted plants still remains unclear. In the proposed, the total amount of P.euphratica will be estimated by Ryel model, and subsequently the relationships among HR amount, richness, abundance, and plant’s drought tolerance will be tested to reveal the effects of HR on biodiversity and the distribution pattern of shallow-rooted plants. Then, the difference of nutrient contents between redistribution and non-redistribution area will be determined in order to clarify the effects of “fertile island” and “crown interception” on HR. In addition, the simulated control experiment will be employed to examine the positive feedback between deep- and shallow-rooted plants for water and nutrient in contrasting HR and “fertile island” and “crown interception” treatments, and to verify the effectiveness of HR on biodiversity in arid desert. The aim of the proposed project attempts to improve our understanding of the physiological mechanism that sustains plant diversity in the arid desert region, and thus providing a potential recommendation to conserve the rare natural resources in Xinjiang region.

深根系植物的水分再分配能改变干旱荒漠的水分分布格局，诱导浅根系植物在水分再分配的发生区域富集，使水分和营养在深浅根系植物间形成正反馈，影响生物多样性过程。但至今对于此过程研究往往是忽略的。本项目选择艾比湖荒漠杜加依林的建群种胡杨为对象，首先，利用Ryel模型估算胡杨的水分再分配水量，后结合再分配区域物种的丰富度、多度和多样性指数，分析胡杨水分再分配对植物多样性的影响；其次，通过比较营养物质含量在再分配区域和未分配区域间的差别，以及营养物质含量与水分再分配水量的关系，阐明“肥岛效应”和“树冠截留”对水分再分配的正向促进作用；最后，设置控制实验，验证胡杨水分再分配对荒漠杜加依林多样性维持的影响。本项目旨在深化和完善干旱荒漠区的核心生态学理论，也为指导干旱荒漠区重要特殊生物资源的保育提供科学依据。

深根系植物的水分再分配能改变水分在空间的分布格局，在水分作为限制因子的干旱区，其可能对物种多样性、植物的空间分布、生长情况等产生影响。本项目利用同位素示踪、建模、样地调查和控制实验等方法，验证和研究了深根系植物的水分再分配现象，水分再分配与生物多样性、生态位、物种空间分布和土壤酶活性之间的关系，水分再分配发生的生理学机理，荒漠植物的水分来源等内容。结果表明：荒漠深根系植物胡杨和梭梭均存在水分再分配现象，且其发生层随季节从土壤浅层向深层迁移；物种多度、丰富度、生态位、生态多样性、空间格局和土壤酶活性在水分再分配发生和未发生的区域均存在显著差别；深根系植物对水分和矿质营养的需求权衡造成最小水势层随季节从土壤浅层向深层迁移，水势在土层之间的差异是水分再分配发生的决定因素；深浅根植物的水分来源不同，深根系植物主要利用地下水和深层土壤水，浅根系植物水源多样，可利用多种水源，比如凝结水、浅层土壤水；除水分再分配外，荒漠内植物多样性还与土壤盐分有关，在含盐量增加梯度上，植物多样性降低。综上可知，深根系植物(胡杨和梭梭)的水分再分配通过改变水分、盐分和土壤酶活性等改善了小环境的条件，诱导浅根系植物在水分再分配的发生区域富集，从而对荒漠生物多样性维持具有正向影响。本研究结果对深化和完善干旱荒漠区核心生态学理论、指导干旱荒漠区重要特殊生物资源的保育，都可以提供重要的科学依据。