我国西南喀斯特区石灰土中有机质与钙离子相互作用研究

Limestone soil is the characteristic soil of the Karst region of southwest China. Previous studies had indicated that the distribution and the evolution of soil organic matters along limestone soil profiles are notably different from those along the profiles of other soils. The higher content of calcium in limestone soil was deemed as one of the possible mechanisms of soil organic matters being preserved in the limestone soil, the interaction of calcium ions with soil organic matters should be one important process commonly happened in soils of the Karst region of southwest China. However, there are very few studies to dig into this process systematically and quantificationally. In this proposal, we try to establish a new method of combining macroscopic simulation experiments with microscopic instrumental analyses to quantify the interactions of calcium and soil organic matters in limestone soils, to investigate the major chemical characteristics of soil organic matters complexing with calcium ions and their pathways in the soil profile, to measure parameters for describing the complexing behaviors of calcium and soil organic matters, and to evaluate effects of calcium concentration to the mineralization ratio and the anti-leaching ability of soil organic matters. The objective of this proposal is to quantitatively assess impacts of the coupling geochemical process of calcium and soil organic matters in limestone soils on the soil evolution, the soil conservation, and the ecological environment restoration of the study area, to bring in some new data to the Karst critical zone researches, and to provide the theoretic guidance for protection and restore soil resources in the Karst region of southwest China.

石灰土是我国西南喀斯特地区的特征性土壤。前期的研究发现石灰土有机质在土壤剖面上的分布和演化显著不同于其他类型土壤，研究认为石灰土中较高的钙含量是石灰土有机质受到保护的重要原因，钙与有机质的相互作用是喀斯特土壤单元中的一个重要地球化学过程，但对于此过程的系统与定量研究还十分缺乏。本项目拟摸索并建立一套宏观模拟实验和微观仪器分析相结合的研究方法，定量研究喀斯特石灰土中钙离子与有机质的相互作用，揭示石灰土中钙结合态有机质组分的化学特性，研究钙离子与有机质在土壤垂向剖面上迁移的相互影响，测定钙与土壤有机质不同组分发生络合反应的强度和有关参数，评估不同浓度钙离子对土壤有机质矿化速率和抗淋洗能力的影响。综合分析数据，尝试定量评估钙离子和土壤有机质耦合地球化学过程对于西南喀斯特地区土壤演化、水土保持和生态恢复的意义，为喀斯特关键带科学研究提供新的基础数据，为研究区土壤的保护与重建提供理论指导。

本项目采集和研究表征了西南喀斯特地区特征性土壤石灰土样品，设计并搭建了多仪器联用的实验研究平台，深入研究了石灰土胡敏酸（HA）与钙离子在水溶液中相互作用的过程与机制，认为石灰土HA与钙离子的结合是络合反应与吸附作用共同控制的复杂过程；与同区其他土壤对比，揭示了石灰土HA的化学组成和赋存形态的特征，发现石灰土HA的相对含量较低且包裹态和结合态HA含量高，认为钙离子的络合与桥键作用是石灰土HA组成与赋存特征的主要影响因素，并探讨了石灰土土壤有机质（SOM）组成与赋存特征在人为扰动后石灰土容易退化流失的自然现象的内在联系；设计并搭建了研究流水驱动下土壤溶解有机碳（DOC）在土壤垂向剖面的迁移与分异的土柱淋洗实验平台，模拟研究了喀斯特地区高钙水体对喀斯特主要土壤中DOC演垂向剖面的迁移与分异规律，发现水体钙离子浓度升高，不但降低了土柱DOC的淋失速率和总量，而且导致淋出DOC的表观分子量增大、芳香性降低和极性增大；土壤水分钙离子浓度对石灰土SOM矿化影响研究发现钙离子浓度高土壤SOM矿化受到一定的抑制。项目研究的结果与结论对西南喀斯特地区土壤退化防治、土壤质量改良和生态环境修复具有基础理论价值和数据支撑意义。