晋西北丘陵风沙区人工恢复林草植被与土壤水热环境的互馈机制

The Sandy-hilly region in northwest Shanxi belongs to the seasonal frozen soil region in China. The climate varied dramatically and the water and wind erosion occurred severely. It is the most extremely fragile eco-environment in Shanxi province and also an important part of the ecological sensitive and fragile crisscross area of farming-pastoral zone in northern China. The soil desiccation has become very serious over this area during the recent decades, which has lead to the severe degradation of the artificial forests and grasslands in this area. Further researches on the soil water and heat environment for the artificial restoration vegetation are urgently needed. At present, most researches on soil water for the artificial restoration vegetation are focus on the plant growing seasons, but less research on the soil heat. Meanwhile, there is almost no research considered the effects of soil water, heat and water-heat coupling for the artificial restoration vegetation during both freezing-thawing and non freezing-thawing periods. Therefore, this research project base on Wuzhai ecological experimental research station, take the methods of the combination of field investigation sampling, experimental observation, laboratory analysis and soil-plant-atmosphere transfer model. The objectives of this research project are to study the soil water, heat and water-heat coupling transfer characters for the farmland, forest and grassland ecosystems during both freeze-thaw and non freeze-thaw periods and further to identify the cause and mechanism of soil desiccation. In addition, it aims to illustrate the mutual responses and feedbacks between artificial vegetation growth and soil water-heat environment, to determine the carrying capacity of soil water resources and appropriate artificial vegetation restoration intensity. It can provide a scientific basis for vegetation restoration and ecological environment construction in the region of northwest Shanxi.

晋西北丘陵风沙区为季节性冻土区，气候变化剧烈，土壤侵蚀强烈，土地沙化严重，是山西省生态环境极脆弱区，是中国北方生态敏感脆弱的农牧交错带的重要组成部分。近年研究区出现土壤日趋干燥化导致人工林草植被开始退化的现象，急需对人工恢复植被土壤水热环境进行深入研究。目前针对该区植被恢复下土壤水分的研究多集中于非冻融期，且对土壤热环境研究较少，而系统并综合考虑冻融和非冻融期植被恢复与土壤水、热及水热耦合效应的研究鲜有报道。本项目拟依托山西大学五寨生态试验站，采用野外调查取样、实验室分析、原地定位观测和土壤－植被－大气生态系统模型相结合的研究方法，研究冻融和非冻融期农地、人工柠条林地和苜蓿草地生态系统土壤水、热及水热耦合运移特征，揭示土壤干燥化成因及机理，探讨人工恢复植被与土壤水热环境相互响应与反馈机制，确定该区土壤水资源承载力及适宜的林草植被恢复强度，为晋西北地区植被恢复建设提供科学依据与参考。

晋西北丘陵风沙区近年出现土壤退化现象导致植被退化现象，需对土壤水热环境进行系统研究，本项目依托山西大学五寨生态试验站，采用野外调查，实验室分析，原地定位观测和土壤-植被-大气生态系统模型相结合的方法，确立土壤水热运移方程，重点研究了农林草地土壤水热运移过程和特征，并利用模型多因素多过程输出的结果，分析了植被恢复条件下土壤环境状况，归纳出以下结果：（1）模型很好的模拟预测了土壤温度和热效应过程，土壤温度年际变化随土壤深度的加深而变小，且随气温变化而变化，但呈现滞后现象，太阳辐射和植被表层覆盖率都会影响土壤温度。晋西北丘陵区土壤温度8月初最高。不同深度土壤，最低温和最高温以及它们的变化幅度存在差异。不同植被的土壤温度时间和空间动态变化大概保持一致；（2）模型在土壤水分模拟方面模拟预测精度低于土壤温度，但仍有借鉴指导作用，土壤剖面水分模拟预测结果显示，随着土层的加深，土壤含水量的波动在减小，浅层土壤水分受到降雨等因素影响较大，在160-185 cm土壤深度以下，水分波动已基本达到稳定，波动较小，土壤水分年际变化也随土壤深度的加深而变小，且随降水的变化而变化；（3）土壤含水量时间动态特征可以根据一年季节的改变，大概分为冬季稳定期、春季损耗期、夏季累积期。土壤水分含量在垂直方向上的动态特征大致为，20～40cm土层最高，60～80cm土层最低；（4）在苜蓿田中存在优先流路径（即苜蓿根）导致高度连续的优先流动。大孔隙流动绕过压实的土壤，被限制在两个独立的斑块中，成为常规耕作田的主要流动行为。保护性耕作系统不仅改善了大孔隙系统的连续性和连通性，也使优先流形成倒三角分布。大孔隙系统的连续性和连通度从最高到最低的顺序是苜蓿、保护性耕作田、未开垦土地和常规耕作田。鉴于大孔系统的连续性和连通性以及土壤蓄水能力在利用未开垦土地方面发挥了关键作用，我们建议地方政府和农民更多的采取苜蓿田和保护性耕作的管理方式。