侵蚀环境下植物群落根系对坡面水蚀过程的影响及机制

Plant roots play a dominant role in reducing soil erosion, and it is an important link to control soil water erosion of temporal and spatial patterns of roots growth. Based on severe soil and water loss in Danjiangkou Reservoir Area and grass-shrub community as main research object, and root effect on regulation of runoff generation mechanism as the research mainline, a combined method of field survey and sampling, plot monitoring and simulated experiments will be employed. The purpose of the research were, under different soil erosion conditions, (i) to determine species composition of plant community, and temporal and spatial variation of roots characteristics and their chemical composition contents; (ii) to analyze mechanism and effects of roots on hydrodynamic characteristics of runoff, soil detachment and soil anti-erodibility; (iii) to understand relative contribution of physical consolidation of soil and root exudates on soil erosion-resistant capacity, developed the regression equation between the adjustment root characteristics and soil erosion process of hilislope including roots. These can clarify the mechanism of the roots of typical plant communities on soil water erosion dynamics process. The results of the research would be important to understand the effect of vegetation on runoff erosion process and soil erosion prediction, and be very useful for soil and water conservation planning of Danjiangkou Reservoir Area.

植物根系对抑制土壤侵蚀有着非常重要的作用，不同立地条件下根系在土壤中演变的时空动态变化是控制土壤侵蚀的重要环节。本项目针对丹江口库区水土流失仍然严峻的现实，以草灌植物群落为主要研究对象，以根系对坡面水蚀过程的调控作用为研究主线，以根系提高土壤抗侵蚀性能为契入点，采用野外调查与采样、原位观测和模拟实验相结合的方法，研究库区不同侵蚀环境下典型植物群落的物种组成、根系特征和化学成分含量及时空变化，系统分析植物群落根系对坡面流水动力学特性、土壤分离过程、土壤抗蚀性的影响及机理，辨析根系物理捆绑固结作用和根系分泌物等生物化学作用对土壤分离的相对贡献，发展根长密度等参数与土壤可蚀性间的数学模型。在此基础上，阐明侵蚀环境下植物群落根系对坡面土壤侵蚀阻控的影响及动力学机制，为全面认识植被抵抗径流侵蚀动态过程和土壤侵蚀预报提供理论依据，为丹江口库区水土保持规划提供科技支撑。

植被恢复是控制土壤侵蚀和修复退化土壤功能的最主要生态措施。植被恢复过程中，根系通过对土壤的物理固结和生物化学粘结作用影响土壤抗侵蚀性能，其在土壤侵蚀控制中作用是无法替代的，在土壤侵蚀预报中也越来越受到关注。然而，根系是一个错综复杂并具有适应性的系统，其性状不仅与植物本身特性有关，且很大程度上与环境有关，呈现显著的时空变异特征；深入认识侵蚀环境下根系的这种复杂适应性是理解植被控制土壤侵蚀的主要环节。项目通过野外调查、原位观测和控制试验相结合的方法，重点开展了：演替梯度下植物群落根系特征及对土壤抗侵蚀性能的影响，草本植物根系季节动态及对土壤抗侵蚀性能的强化效应，侵蚀环境下植物功能性状及对土壤保持功能影响及机制等方面的研究。重要结果有：①明确了丹江口库区五龙池小流域演替梯度下的植物群落及根系特征，发现随着演替的进行，土壤中优先流数量增多且运移路径增大，根系特别是直径小于2mm的细根显著影响了优先流的产生与发展。②阐明了2种草本植物全生育期内根系的季节变化特征，识别了降低土壤分离能力的最适植物种植密度及最佳根系径级，发现根长密度是影响土壤抗侵蚀性能最重要的因子。③发现侵蚀程度和植被类型显著影响植被盖度和根系径级分布，但对根径范围无显著影响；明确细根长密度和土壤抗剪强度分别是根系性状和土壤结构性质中与土壤分离能力联系最为紧密的两个变量；构建了基于根系功能性状、土壤物理性质和水动力参数的土壤分离能力预测模型。④明确了侵蚀环境下植被植物功能性状对土壤保持功能的影响及机制，并由此提出一种土壤侵蚀退化的修复框架。结果可为对丹江口库区侵蚀退化地植被恢复提供实践策略和理论指导。