绿洲-荒漠过渡带植物群落水分利用过程研究

Through two years researches supported by the National Natural Science Foundation of China (Grant No. 40901061), we have understood plant communities composition, structure and spatial distribution pattern in the oasisi-desert ecotone in the lower Tarim River; discussed the response and adaption of photosynthesis and hydraulic conductivity to water and temperature stresses; clarified the decline and succession process of plant communites; analyzed the relationship between plants diversity and environmental factors and determined the soil layers closely related to plant communities stability; determined the rational groundwater depths of plant populations and plant communites; reconstructed the composition mode of plant communites to maintain ecological stability in the oasisi-desert ecotone. Since the implementation of the project, we have published more than 10 papers and completed 5 registration of computer software. . In this project, different plant communities along water stress gradients in oasis-desert ecotone in the lower Tarim River were chose as the research objects . Water sources of different plant communities were studied using the multiple source mass-balance isotopic approach to discuss water use and water distribution patterns and reveal the maintaining mechanism of the plant communites formation and distribution in the oasis-desert ecotone. Dynamic process, effect factors and ecological effects of xylem hydraulic conductivity of different plants were analyzed based on field investigation and test of water stress control at laboratory. It was used to reveal the regulation and adaptation mechanisms of hydraulic conductivity to water stress and discuss plant communities survival strategy to different water stresses combined with the root morphological and spatial distribution characterstics. Evapotranspiration model including plant physiological and ecological processes was constructed through analyzing plant transpiration process and mechanism to calculate evapotranspiration of plant communites in oasisi-desert ecotone and put forward to the management strategies for protecting the ecological stability of oasis - desert ecotone under the oasis drip mode.

青年基金项目（40901061）经过两年分析研究，已探明了绿洲-荒漠过渡带植物群落组成、结构和空间分布格局；解析了植物光合和木质部导度对干旱胁迫和高温等环境胁迫的响应与适应；阐明了绿洲-荒漠过渡带植物群落衰退演替过程及植物多样性与环境因子的关系；确定了维持绿洲-荒漠过渡带植物种群与群落稳定的合理生态水位，并构建了绿洲-荒漠过渡带稳定的群落组成模式。发表文章10篇、软件登记5项。.本项目以绿洲至荒漠不同演替阶段植物群落为对象，采用稳定同位素技术分析不同植物群落水分来源，探讨植物水分利用与分配方式，揭示群落形成与分布的维持机理；开展不同类型群落植物水分传导的动态过程、控制因素与生态效应研究，提出水分输导对水分胁迫的调控与适应机理，探讨植物群落的生存策略；构建基于生理生态过程的植物蒸散发评估模型，计算过渡带植物群落蒸散耗水量，提出绿洲农业滴灌模式下保护绿洲-荒漠过渡带生态稳定的管理对策与措施。

本项目结合4年（2013-2016）来在塔里木河下游荒漠-绿洲过渡带进行的植被、水、土生态调查和植物生理生态指标测定，解析了干旱区植物水分来源，阐明了干旱胁迫下植物水分吸收、分配、传导和蒸腾的响应过程和适应策略，提出了塔里木河下游建群植物胡杨和柽柳根系吸水主要来源于375cm土层以下的地下水；胡杨根系具有明显的水分再分配作用，水力提升主要发生在10-110 cm 土层，日均提升水量为0.41 mm，提升水量占耗水量的32%；地下水位埋深<4m时，荒漠植物是通过枝条木质部限流来适应轻度干旱胁迫，而地下水位埋深>6m时，荒漠植物水流阻力主要发生在根部；极端干旱胁迫下，荒漠植物通过减小气孔开度，降低水分耗散来适应水分亏缺，柽柳对干旱胁迫的适应性强于胡杨；探讨了胡杨对盐分胁迫的响应与适应机制，指出盐分胁迫限制了胡杨根系生长，降低了根木质部导水速率，显著加剧了木质部栓塞脆弱性，在轻度（0.05 Mol/L NaCl溶液）和中度（0.15 Mol/L NaCl溶液)盐分胁迫下，胡杨通过协调导管输水的有效性和安全性来调节木质部的导水率，重度（0.30 Mol/L NaCl溶液) 盐分胁迫下，胡杨茎木质部导管输水有效性和安全性均明显降低，严重抑制了胡杨的光合和生长；重建和评估了研究区地下水埋深历史变化过程和荒漠植物生态需水量，提出如要保证塔里木河下游英苏断面胡杨维持多年（1933-2015年）平均径向生长，每年需从大西海子水库下泄生态水量0.84×108m3；如要保证胡杨达到断流前（1933-1974年）的平均径向生长，则每年需从大西海子水库下泄生态水量0.91×108m3。