人为干扰胁迫下喀斯特峰丛洼地土壤养分的快速流失机制

Rocky desertification, a land surface process of rapid decline in vegetation cover and ecosystem service, has been observed extensively in karst peak-cluster depression area in southwest China since 1960s as a result of fast-growing population and intense utilization of land resources. karst peak-cluster depression ecosystems are extremely vulnerable to human disturbance resulted from its thin soil cover, dual structure of hydrological processes, and rapid loss underground of water. Recently, we found the accelerated loss of nutrients under human disturbance is one of the most important key processes which drive the occurrence and development of rocky desertification in this area, but we still know little about the mechanisms cause the pattern of nutrient loss. Based on field disturbance experiment (removal of vegetation, tillage, no-till and undisturbed ecosystems), this project intends to evaluate nutrient protection mechanisms in different soil organic matter (SOM) pools in soil aggregates and identify the association of Ca2+ with total organic carbon (TOC) under the influence of different disturbance; and to analyze the correlation between the transformation and the critical value of soil nutrient leaching and soil properties, soil temperature, soil water content, so as to find out the key factors controlling the transport of soil nutrients; and to survey the variability of soil erosion, soil nutrients leaching and soil gas emission, and use model simulation to calculate the amount of soil nutrient loss across different process, so as to identify the main pathway of nutrient loss, clear its influencing factors, and reveal the mechanism of rapid losses of soil nutrients under human disturbance in karst peak-cluster depression landscape. The results will provide scientific basis for the ecological recovery and rocky desertification control in the karst peak -cluster depression region southwestern China.

西南喀斯特峰丛洼地生态系统脆弱，土层浅薄、二元结构发育、水文过程变化迅速，在人类干扰胁迫下，土壤养分也呈现出快速流失的特征。但是目前对土壤养分迁移、转化的快速响应机制还缺乏充分认知，使得石漠化治理工作的开展难以深入。本项目针对这一关键科学问题，以土壤有机质（SOM）稳定性为切入点，基于长期定位控制试验（耕作、砍伐等），分析土壤各粒级团聚体SOM组分和钙（Ca）形态的变化，明确干扰对峰丛洼地土壤养分形态转化的影响；同时通过土壤侵蚀、养分淋失等过程的连续监测，探明土壤碳（C）、氮（N）、磷（P）的迁移形态和迁移规律，探讨其与土壤环境因子（地形、水分、温度及土壤理化特征）的关系，阐明养分流失的主要途径及主要影响因素；利用水量平衡和模型模拟方法评估各个途径对养分流失的贡献，揭示干扰作用下土壤养分的快速流失机制，为喀斯特峰退化生态系统的恢复重建和有限土地资源的可持续利用提供科学依据。

西南喀斯特峰丛洼地土层浅薄、表层岩溶带发育，水文过程以地下垂向和侧向过程为主，且水文过程迅速。虽然喀斯特地区自然生态系统土壤碳氮养分含量高于同纬度非喀斯特地区，但一旦受人为干扰胁迫，其碳氮养分迅速丢失，长期不合理土地利用将导致土壤退化。但目前对干扰胁迫下该地区土壤碳氮养分的矿化丢失机制及其主要丢失途径还缺乏充分认知，使得石漠化防治工作的开展难以深入。本项目针对这一问题，通过开挖岩土断面，采用野外调查、原位控制试验和室内培养试验相结合的方法，对“岩石-土壤-水分”系统各个界面的碳氮养分迁移转化过程及其对人为干扰胁迫的响应进行了研究。研究结果发现：（1）不同干扰/利用方式（砍伐、火烧、耕作等）中，仅扰动土壤的农业利用方式（牧草和玉米种植）对土壤有机碳（SOC）、全氮（TN）和大团聚体碳氮影响显著，土壤大团聚体组分和大团聚体有机质（SOM）储量的减少是碳氮丢失的主要原因。（2）人为干扰下土壤碳、氮的丢失途径不同，SOC主要以CO2排放的形式丢失，而TN主要以硝态氮组分形式通过表层岩溶带侧渗和深层渗漏等地下途径流失。（3）传统农田翻耕导致土壤团聚体平均质量半径减小，大团聚体破坏，受大团聚体保护的闭蓄态有机碳转化为游离态和可溶性有机碳并迅速矿化丢失，导致CO2排放增加，氮素淋失。以上研究结果表明，喀斯特退化生态系统的恢复管理应防止土壤物理破坏，为土壤微生物营造适宜的生境，促进土壤有机质的积累，研究结果可为喀斯特山地土地利用结构优化和土壤退化阻控提供科学依据