干旱区绿洲防护林植物-土壤水盐-地下水相互作用研究

The wind shelters of oasis in the arid region of Northwest China are crucial to the environment, agricultural production, and human being life. The wind shelters have been deteriorating in the last two decades attributed to groundwater level dropping and salt accumulation in root zone of the trees. The objectives of this proposal are to understand the intrinsic mechanisms involved in the groundwater - soil water and salts - plant - atmospheric continuum (GPSAC), and to investigate the key factors influencing the wind shelter tree evapotranspiration. The field observation of the wind shelter GSPAC will be conducted in the Manas River oasis of Xinjiang, focusing on the interaction between plant evapotranspiration and soil water and salt, the influences of groundwater upon soil water and salt through capillary rise. On the basis of field observation, we attempt to improve the modeling approach of evapotranspiration with consideration of wind shelter effects, and the approach of salt stress to tree evapotranspiration, develop a GSPAC model, simulate the complex interactions among the GSPAC components under variable groundwater, soil water and salt, and weather conditions, and identify the key factors that affect the wind shelter tree evapotranspiration will be identified.

绿洲防护林是我国西北干旱区绿洲农业生态安全维护屏障，近年来由于绿洲灌溉用水方式的改变，出现了明显的衰退现象，主要原因可能是地下水位的下降和土壤盐分的变化。本项目以玛纳斯河流域绿洲防护林为例，通过野外试验观测，研究防护林的植物-土壤水盐-地下水系统中水分和盐分运移过程，阐明这一体系中植物-水盐的相互作用关系，研究土壤盐分对植物耗水胁迫的理论方法，防护林带状分布情况下的蒸腾计算方法，并在成熟的地下水-土壤-植物-大气连续体(GSPAC)模型，如HYDRUS的基础上，开发适应于防护林与土壤水盐相互作用的连续体模型，模拟研究变化的气象要素、地下水位、土壤水盐条件下，防护林耗水规律，识别主要影响因素，提出控制指标，为绿洲防护林管理提供科学依据。

绿洲防护林是我国西北干旱区绿洲农业生态安全维护屏障。近15年来，由于绿洲灌溉用水方式的改变，出现了明显的衰退现象。本项目中，以玛纳斯河流域绿洲为例，采用野外试验观测与模型模拟的方法，研究防护林土壤水、盐运移过程与植物蒸腾耗水规律，主要研究成果为:.(1)根据气孔导度与环境因子关系，构建了Jarvis形式的气孔导度公式。.(2)开发了防护林植物-土壤水盐动态模拟模型。在植物-土壤水分模拟模型基础上，增加土壤盐分运移过程模拟；研制了防护林冠层辐射计算、与土壤水盐耦合作用的根系生长模拟、基于根-茎-叶水分传输的蒸腾计算方法。.(3)确定了土壤水分对防护林蒸腾与生长的关键阈值。当土壤有效含水率低于0.75时，对植物气孔导度开放具有胁迫作用，低于0.45时，气孔导度几乎完全关闭，较长时间的土壤水分胁迫对植物的损害不可逆。.(4)评估了玛河绿洲农田防护林蒸散与灌溉需水量。充分保障蒸腾需水养护时，玛河绿洲防护林时的总蒸散量为875mm,年灌溉需水量为616mm；最低土壤水分要求养护下，需要年灌溉需水量398mm。.本研究阐明了防护林土壤水-盐运移过程以及对林木蒸腾胁迫作用机制，研究成果可为绿洲农田防护林管理提供科学依据。