黄土高原不同年限灌草植被土壤水分植被承载力研究

Over the past decades years, the ecological environment reconstruction, especially, vegetation restoration has made important achievements on the Loess Plateau. However, many regions show the new contradictions between water resources shortage and ecological environment, such as, a dried soil layer is universal formed in the soil profile under artificial vegetation. The main cause of this phenomenon is lack of insight understanding of the mutual relationship among soil moisture, vegetation and climate. Therefore, it is necessary and crucial to further study about quantization of the degree of vegetation restoration and the dynamic relationships among soil moisture, vegetation and precipitation. This project will be conducted on Liu Daogou watershed in the north of Shaanxi on the Loess Plateau, and we chose artificial shrub (Caragana korshinskii Kom., caragana) and grass (Medicago sativa, alfalfa) on plot and slope scale as the research object to carry out the experimental study. Field monitoring, laboratory analysis, data collection, and model simulation will be combined. We aim to investigate the response of soil water dynamics and plant growth to growth years and annual precipitation patterns for caragana and alfalfa; to quantitate soil water carrying capacity of vegetation for caragana and alfalfa under different growth years; and to validation the simulation results under different growth years and annual precipitation patterns using field experiment data. This research will be conductive to deepen understanding the dynamic relationships among soil moisture, vegetation and precipitation in the construction of artificial vegetation. The results of this research will also provide a scientific basis for quantitating soil water carrying capacity of vegetation on the Loess Plateau.

近几十年，黄土高原以植被恢复为主的生态环境重建取得了重要进展，然而由于对土壤水分-植被-气候间相互关系缺乏深入了解，很多地区表现出新的水资源－生态环境矛盾，如土壤干化现象普遍出现。有关植被恢复程度量化和土壤水分-植被-降水间动态关系调控等研究还需加强。为此，本项目选择陕北黄土高原六道沟小流域为研究对象，在小区和坡面尺度上，采用野外观测、室内分析、资料收集及模型模拟相结合的方法，分析两种灌草植被（柠条和紫花苜蓿）随生长年限和不同降水年型的植被生长特征和土壤水分时空动态，基于过程模型量化不同年限下柠条和紫花苜蓿的土壤水分植被承载力，并结合野外试验，验证模型对柠条和紫花苜蓿在不同生长阶段和降水年型下的预测结果。研究结果有助于深化认识黄土高原人工植被建设中土壤水分-植被-降水间动态关系，为土壤水分植被承载力量化机制建立提供科学依据。

近几十年，黄土高原以植被恢复为主的生态环境重建取得了重要进展，然而对人工植被恢复程度量化和土壤水分-植被-降水间动态关系调控等研究还缺乏深入了解，土壤干化现象普遍出现。为此，本项目选择陕北黄土高原六道沟小流域两种典型人工灌草植被（柠条和紫花苜蓿）为研究对象，分析生长年限和不同降水年型对柠条和紫花苜蓿的植被生长特征、土壤水分时空动态和水分消耗特征的影响，并量化了柠条和紫花苜蓿的土壤水分植被承载力以及土壤干层内水分恢复动态过程。结果表明：6年生柠条和5年生苜蓿地剖面土壤水分变化速率均存在“拐点”，柠条和苜蓿种植前5年土壤水分迅速减少并形成土壤干层，之后土壤水分减少速率降低。种植8年后，4m剖面中的土壤储水被消耗殆尽，土壤水分处于相对稳定状态。因此，柠条和苜蓿的适宜的生长年限分别为6年和5年，其对应的土壤水分植被承载力（地上最大干生物量）分别为5050kg/hm2和1980kg/hm2。不同降水年型下，相比自然草地而言，柠条和苜蓿植被长期单一种植显著加剧了土壤水分的减少，且水分循环通常限制在较浅土层，对1.0m以下土壤水分动态影响很小。极端丰水年降水只能对柠条和苜蓿地2.0m深度内干层的土壤水分有短期补给恢复效应。因此，黄土高原植被恢复可以考虑耗水较少的物种或以自然恢复为主。通过建立土壤水分运动过程模型，模拟分析了16a生柠条和15a生苜蓿地进行自然恢复后，不同恢复年限下土壤水分动态和干层恢复情况，土壤水分恢复至干层消除分别至少需要6年和13年的时间。研究结果有助于深化认识黄土高原人工植被建设中土壤水分-植被-降水间动态关系，为土壤水分植被承载力量化机制建立提供科学依据。

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