黄土区典型灌草植被土壤干层内水分的利用-补给过程与机制

A dried soil layer (DSL) is generally formed in the soil profile in the artificial shrubland and grassland across the Loess Plateau. After the formation of DSL, soil water retained within the DSL (SW-DSL) can be further uptaken by the root system. This part of the precious water is very important to the survival of plants in extreme dry seasons in the arid and semi-arid loess regions. We have, however, poor knowledge on the utilization and recharge processes and the associated mechanisms of SW-DSL for different plant species, limiting the scientific utilization and management of this part of water. This project will be conducted in two small catchments of the loess area. Selected species will be two typical artificial plants, i.e., caragana and alfalfa, widely cultivated in the loess area. A combination of filed location observation, soil column simulation experiments, isotope labeling techniques, and mathematical models will be used as a research tool. We aim (1) to characterize water movement processes in the DSL and at the interfaces between DSL and non-DSL (including the upper boundary and the lower boundary), (2) to clarify the processes and mechanisms of depletion and recharge of SW-DSL, (3) to ascertain the relative proportion of soil water uptake from DSL and other layers and its seasonal dynamics, and (4) to reveal the dynamic relationship between root water uptake rate and soil water content under low water potential conditions and the associated mechanisms. This research is of great scientific significance to understand the dynamic functions of SW-DSL. Moreover, it helps to strengthen the soil water management and provide scientific basis for the sustainable growth of artificial vegetation, as well as the regulation of DSL in the arid and semi-arid loess area.

黄土高原人工灌草植被土壤干层广泛分布。土壤干层形成以后，干层内土壤水分仍可被植物根系吸收和利用，这部分宝贵的水源是干旱和半干旱黄土区人工植被应对极端干旱的"救命水"。然而，该区干层内水分的利用和补给过程及其影响机制尚不明晰，加大了对这些水分科学利用与管理的难度。本项目以黄土区广泛种植的柠条和苜蓿为研究对象，通过野外定位观测和土柱模拟试验，结合同位素标记技术和数值模拟，分析土壤干层内和干层界面处的水分运动过程，探明干层内水分的消耗和补给过程及其影响机制，明确植物根系对干层和非干层中水分利用的相对比例与动态特征，揭示低水势条件下根系吸水速率与土壤含水量的动态关系及其影响机理。研究结果对深入认识干层内水分的生态功能具有重要科学意义，同时有助于加强土壤水分管理，为有限降水条件下黄土区人工植被的可持续生长及干层调控提供科学依据。

黄土高原人工灌草植被土壤干层广泛分布，干层内水分对维持植被生态系统可持续具有重要作用。项目围绕植物根系利用水源的辨识和土壤干层内水分对植物的有效性两个关键科学问题，在定位观测、区域调查、田间试验和模型模拟基础上，探明了典型灌草植被柠条和苜蓿对干层和非干层中水分的消耗特征与季节动态，确定了柠条和苜蓿水分生理特征对土壤干燥化的响应阈值，量化了黄土区土壤干层内水分对植物的有效性，建立了土壤水力性质预测的传递函数模型，揭示了黄土区土壤水力性质的空间分异特征，模拟分析了典型灌草植被土地利用变化情景下土壤干层内水分的补给恢复过程及影响机制。项目共发表论文18篇，在Journal of Hydrology、Geoderma、Science Bulletin等期刊发表SCI收录论文14篇(其中第一标注SCI论文4篇)，CSCD收录论文4篇(其中第一标注3篇)，完成了任务书指标(发表学术论文6−8篇，其中SCI收录论文4篇以上)。培养研究生3名。项目执行期间，项目负责人获得国家自然科学基金优秀青年基金(2020年)，入选中国科学院青年创新促进会优秀会员(2021年)，获得陕西省自然科学一等奖(2020年，排第4)和宁夏回族自治区科技进步二等奖(2020年，排第4)。提交了关于加强草地建设，防控黄土高原风沙区水资源过度消耗和农田沙化的建议咨询报告。项目成果对深入认识土壤干层内水分的生态功能以及土壤水分可持续管理和干层调控具有重要的科学和实践意义。