基于植被动态的黄土小流域土壤干燥化信息图谱研究

Soil moisture is the key limiting factor for plant growth and ecosystem services in semi-arid areas. The spatial and temporal patterns of soil moisture have significant influences on many ecosystem processes. Soil desiccation due to excessively soil water consumption by large-scale vegetation restoration has become an important limitation for ecological restoration in the Loess Plateau. Understanding the influence of heterogeneity and dynamics of vegetation on soil desiccation process, and identifying and modelling the spatial and temporal variations of soil desiccation at different scales are urgent and necessary issues for current studies. This can provide scientific guidance for sustainable vegetation restoration in this region. A small typical loess hilly watershed in semi-arid Loess Plateau is selected as study area. The temporal variation and spatial distribution of vegetation structure, vegetation coverage, and soil moisture content at the site, hillslope, and watershed scale will be studied based on field observation. Methods including statistical methods, spatial analysis, and model calculation will be used. The response of soil desiccation to vegetation dynamics will be studied, and the quantitative relationship between vegetation pattern and spatial and temporal variability of soil desiccation will be identified in this study. The main affecting factors of soil desiccation at different scales will be explored. The information graphic modelling the spatial and temporal pattern of soil desiccation will be developed based on the relationship between vegetation dynamics and soil desiccation at different scales. The methods of decreasing soil desiccation based on vegetation pattern optimization at different scales would be discussed based on the information graphic of soil desiccation. These results are expected to provide scientific guidance for the vegetation pattern optimization and sustain vegetation restoration in the Loess Plateau.

土壤水分是半干旱区植被生长及关键生态系统服务重要的自然限制因子，研究其动态和时空分配对于区域生态恢复具有重要意义。土壤干燥化是当前黄土高原生态恢复的重要制约因素，从时间和空间上揭示植被动态对土壤干燥化的影响，定量识别和模拟土壤干燥化的时空格局尤为迫切和必要，这也是黄土高原植被合理布局的科学基础。本项目以典型半干旱黄土丘陵小流域为研究区，基于立地—坡面—流域尺度遥感和地面植被动态监测和土壤水分定位观测，辅以数理统计、空间分析和模拟分析等方法，研究植被的动态特征及其对土壤干燥化的作用机制，从不同空间尺度揭示植被格局及其覆盖动态对土壤干燥化时空分异的影响并建立其函数关系，耦合地形特征和土壤属性的影响，构建异质景观中土壤干燥化时空格局信息图谱，探讨基于植被格局优化的土壤干燥化调控机制。本研究将为黄土高原植被建设合理布局和维护植被恢复可持续性提供科学依据。

土壤水分是半干旱黄土高原植被生态系统功能维持的关键限值因子，土壤水分含量及其时空分异受植被动态的显著影响，定量辨识植被动态及其对土壤水分的影响是控制土壤干燥化的前提和基础。本项目基于立地—坡面—流域尺度植被群落组成、功能性状、覆盖动态、水文过程等的定位监测，综合运用多种数据分析方法解析了黄土小流域植被动态与土壤水分的时空耦合关系。研究发现：（1）0~1m深度土壤水分受植被、降雨和地形的综合影响，而植被则是1m以下土壤水分含量、季节动态及其垂直分布特征的决定因素，土壤有机碳等养分的积累以土壤水分的消耗为前提，土壤干燥化会限制深层土壤碳固定并削弱土壤养分保持能力；（2）不同种类植物的功能性状在流域尺度存在空间差异和季节差异，其中叶面积和叶长对土壤水分响应更为敏感，可以作为表征和预测流域土壤干燥化时空动态的指示功能性状；（3）流域植被格局决定了其土壤水分的时空分异特征，人工植被恢复小流域0~2m土壤水分比对照低8.9%~20.4%，2~5m土壤水分低36%，其土壤干燥化具有较高的时间稳定性和空间均质性；（4）构建了流域尺度无人机光学遥感数据植被覆盖度定量识别方法，分析发现生长季不同时期植被覆盖度的空间格局具有一定的时间和空间稳定性，植被覆盖动态同植被类型、空间分布、降雨和地形特征密切相关，植被覆盖度与土壤水分呈负相关关系且受降雨影响显著，流域植被覆盖度的增加是以土壤水分的过度消耗为代价的；（5）不同植被类型在生长季不同时期水分利用的深度来源有所不同，人工植被覆盖小流域水分利用倾向于1~2m深度土壤（48.53±6.21%），且空间异质性较低，以农田和撂荒草地为主的小流域植被水分利用以0~0.4m（33.58±4.35%）和0.4~1m为主（37±3.89%）。本项目将为半干旱黄土高原流域生态系统结构优化与功能提升、流域植被建设的合理布局与优化管理提供关键科学依据。