黄土高原水蚀风蚀交错带典型灌木林水分利用过程对降雨改变的响应

The response of water use processes of different landscape units in the semi-arid area to simulated precipitation variation is not only the foundation for probing the evolution of structure and function of ecosystem under global climate change, but also the focus and hot topic of present research. Most of past researches in this field were mainly concentrated on forest and grasses, and few researches have been conducted on shrubs. Hence, in this study we selected two typical shrubs on the water-wind erosion crisscross region of the Loess Plateau---Caragana korshinskii and Salix psammophila as research objects, and planned to study the water use processes, including root water uptake, hydraulic transport and transpiration, of two shrubs by manipulating precipitation variation through large scale rain-shelter and water addition during dry and wet season, meanwhile, stable isotopes of hydrogen and oxygen will be used to trace the source of root water extraction; finally, a Soil-Plant-Atmosphere (SPA) model were used to simulated dynamic changes of water use and productivity of different treatments. Our aim is to elucidate water use traits of two shrubs and the major process affecting water use under changed precipitation, and demonstrate the adaptation mechanism of these shrubs to precipitation changes under global climate change, thus provide theoretical guide to future vegetation restoration and rehabilitation of this region.

半干旱区不同景观单元水分利用过程对模拟降雨改变的响应是了解未来气候变化背景下该地区生态系统结构和功能演变的基础，亦是当前国内外研究的重点和热点问题。以往这方面研究主要集中在森林和草地上，而对灌木林研究较少。本项目以黄土高原水蚀风蚀交错带两种典型的人工灌木林---柠条和沙柳为研究对象，拟通过修建大型遮雨棚模拟干旱及分别在旱季、雨季开展人工增水实验，系统研究降水改变条件下两种灌木林SPAC系统水分运移过程，包括根系吸水、水分传输和蒸腾，并用稳定性氢、氧同位素联合示踪技术追踪其根系吸水来源变化；在此基础上，用土壤-植物-大气（SPA）模型模拟两种灌木林在不同降水格局下水分利用和生产力的动态变化，试图阐明两种灌木林降水改变下的水分利用特征和水分利用变化的关键环节，揭示全球气候变化背景下灌木林对降水格局改变的响应特征和适应机制，为这一地区未来植被恢复与建造提供科学依据。

半干旱区典型植被水分利用过程对模拟降雨改变的响应是了解未来气候变化背景下该地区生态系统结构和功能演变的基础，亦是当前国内外研究的重点和热点问题。以往这方面研究主要集中在森林和草原上，而对灌木林研究较少。本项目以黄土高原水蚀风蚀交错带两种典型的人工灌木林---沙柳和柠条为研究对象，通过模拟降雨操纵试验（对照、增水45%和遮雨50%），系统研究了降水改变条件下两种灌木林SPAC水分运移过程，包括根系吸水、水分传输和蒸腾，以及生产力的响应。得到了如下主要结果：1）干旱增加了两种灌木根系对深层水分利用，沙柳在旱季主要利用深层土壤水，雨季则主要利用浅层土壤水，而柠条一直维持对深层土壤水分的利用。沙柳通过水分来源的可塑性和生理-形态调节来适应季节性水分变化，而柠条主要依赖生理-形态调节来适应季节性水分变化。2）沙柳为等水型植物，而柠条为异水型植物。沙柳叶水势、净光合速率和气孔导度对增水的响应更强，表现出“不对称性”，而柠条对增水和干旱均有显著的响应，表现出“对称性”。3）沙柳茎木质部比导水率、比叶导水率对增水有显著相应，而柠条对干旱则有显著响应。沙柳不同水分处理正午原位栓塞程度相同，但干旱显著增加了柠条正午原位栓塞程度。沙柳增水处理导管直径和导管面积占边材面积的比例显著增加，干旱处理的导管密度显著增大，水力直径变小；柠条增水处理的木质部结构无明显改变，干旱导致其导管密度和木材密度显著增加。增水提升了沙柳的水力功能，而干旱显著降低了柠条水力功能。4）柠条日蒸腾量和日总辐射、日均蒸汽压亏缺呈显著正相关；当0-40 cm 土壤含水量低于6.7%时，柠条水分利用受到限制。增水使柠条生长季林分水分利用增加21.3%，而干旱则使其下降19.1%；干旱下柠条生物量降低程度大于沙柳。这些结果揭示了两种灌木林在不同降水格局下的水分利用特征，为未来全球气候变化背景下两种灌木林的适应性评价和生产力模拟奠定了理论基础。