基于树干液流监测和穿透雨量调控对黄土高原刺槐人工林耗水特性及其水分响应的定位试验研究

Loess Plateau is one of the major regions in China where vegetation protection and reconstruction have been conducted. Black locust (Robinia pseudoacacia) is the most commonly planted species which accounts for over 300,000 ha of artificial forests in the sub-humid and semiarid areas in Shanxi Province. However, the black locust forests in the semiarid Loess Plateau frequently show problems of low productivity, poor ecological services, and early degradation, which have been related to an imbalance in water demand and supply. In this research, we select two sites which represent semiarid (Yan'an City) and sub-humid (Yongshou County) climates, with annual precipitations of about 500 and 650 mm, respectively. In addition, we also set a reduced-rainfall plot by partially intercepting through fall in Yongshou site corresponding to that of natural condition. Transpiration water use in each forest plot will be monitored by measuring stem xylem sap flow using Granier-type thermal dissipation probes. Meteorological factors, soil moisture conditions and rainfall components (e.g., through fall, stem flow) will be monitored simultaneously. Based on large-sample measurements of stem sap flow (over 2/3 individuals covering all diameter classes), dynamics of stand transpiration water use and their responses to precipitation and soil moisture conditions will be investigated. This will elucidate the regional variations in modification of rainfall components and soil water balance of these plantations. It will further clarify their water use strategies, eco-hydrological effects, stand productivity, stability, and sustainability in relation to different precipitation levels. It is also expected to propose a suggestion for areas of conditional establishment of this artificial forest expressed by prcipitation threshold in the region.

黄土高原地区是我国植被保护和重建的重点区域。刺槐是该地区的主要人工林树种，仅陕西省境内的黄土高原半湿润半干旱地区就有超过30万公顷的刺槐人工林。但是，半干旱区的刺槐林频繁出现生产力和生态功能低下、早期衰退等问题，大量报道显示与水资源供需矛盾有关。本研究将选择年降雨量分别为500 mm（延安）和650 mm（永寿）的两个研究区域，以两个天然降雨量水平和一个人工截留降雨控水处理（永寿）为水分梯度，采用热扩散式树干液流探针对刺槐林蒸腾耗水进行定位监测，同时监测气象环境因子、土壤水分因子以及林内降雨组分分配。基于大样本中长期定位监测推算群落蒸腾耗水动态，分析其对降雨量、土壤水分的响应特征；探明不同降雨水平下的土壤水分收支状况、生态水文功能、群落稳定性和可持续性；揭示其响应不同降雨量的内在生理机制;探索提出刺槐人工林在黄土高原地区有限发展区域的降雨量阈值。

刺槐是黄土高原地区植被恢复的主要树种。半干旱半湿润区的刺槐林存在水资源供需矛盾等潜在问题。本研究选择了年降雨量分别为500 mm（延安）和650 mm（永寿）的两个研究区域，以两个天然降雨量水平和一个人工截留降雨控水处理（永寿）为水分梯度，分析了刺槐林蒸腾耗水对降雨输入、土壤水分因子和气象环境因子的响应特征。研究表明，降水量水平不仅影响土壤水分状况，而且影响刺槐对气象环境因子响应的敏感性。降水输入减少导致的土壤含水量整体降低会使刺槐蒸腾耗水量下降，显示其对环境因子的适应性，但同时也导致生产力的降低。在降雨量不同的两个气候区，刺槐在边材面积、比叶面积和气孔密度等形态学指标方面都呈现一定差异，对于相同胸径的刺槐，延安试验地的边材面积和比叶面积均小于永寿试验地，而叶片气孔密度则大于永寿试验地，此外，两个气候区刺槐在枝条木质部水势和水分利用效率等生理指标方面也呈现差异，这些都与其蒸腾耗水差异相一致。