黄土区大型露天煤矿复垦高压实土壤有机碳恢复机理研究

There are immense space to rejuvenate the carbon sequestration ability in reclaimed ecosystem in opencast coal mines. Nevertheless, the mechanism of carbon sequestration in reclaimed soil is yet to be clarified. Soils are compacted in the process of mining and soil organic carbon (SOC) that is protected by soil aggregate is mineralized subsequently. Fortunately, reclamation alleviates the compacted structures and restores carbon sequestration capacity in mine soils. In this point of view, we develop a program to get insight into the formation of SOC in compacted reclaimed mine soils. Pingshuo Field Scientific Research Base, a reclamation base of the Ministry of Natural Resources, is set to be the study area in the program. Field sampling and experiment analysis of soils and vegetation within different reclamation pattern plots are selected to find out (1) the rule of the development of vegetation biomass carbon, (2)the principle of the SOC recovery and (3) the rejuvenation progress of soil aggregate structure in 0~30 year plots with different reclamation patterns. Furthermore, the amount of new carbon input into density fractions of SOC is detected by carbon isotope technology. The increase and turnover path of density fractions of SOC are tested as well to reveal the process of carbon sequestration in reclaimed soil. The process is at the beginning of the vegetation carbon and end up with the stable SOC. The result of the research could provide an opportunity to observe the development of the compacted mine soil structure and the rejuvenation of SOC, moreover, it provides reference for the study of soil quality succession and carbon cycle in opencast coal mines.

露天煤矿复垦生态系统碳固定潜力巨大，然而目前复垦土壤固碳机理尚不明确。露天煤矿开采破坏土壤结构，造成土壤压实并引起土壤有机碳矿化，土地复垦则可恢复土壤团聚体结构，改善土壤高压实特性并恢复土壤固碳能力。鉴于此，本项目依托自然资源部土地复垦野外科学研究基地—山西朔州平朔矿区土地复垦野外科学研究基地，通过对不同复垦模式样地进行野外采样调查与室内测试分析，探究黄土区大型露天煤矿不同复垦模式0~30a植被生物量碳增长特征、复垦土壤有机碳恢复特征、土壤团聚体结构恢复过程，并利用碳同位素技术，研究土壤团聚体结构恢复过程中不同密度组分有机碳中新碳比重、不同密度组分有机碳增长规律及各组分有机碳之间的周转路径，从而揭示复垦土壤有机碳从植被碳输入到稳定性有机碳（矿质结合碳）形成的过程与机理。研究结果可揭示复垦高压实土壤结构变化特征与有机碳恢复机理，为露天煤矿土壤质量演替和矿区碳循环研究提供参考。

露天煤矿在满足我国能源需求及推动社会经济发展的同时，也给矿区及周边生态环境造成了严重破坏。开展煤矿复垦土壤有机碳恢复研究可为矿区生态系统碳循环研究提供基础。本项目研究结果表明：土地复垦显著提高了土壤C、N活性组分含量，其中，刺槐—油松样地土壤活性碳组分占比显著高于其他复垦样地。土地复垦中的机械碾压破坏了土壤水稳性团聚体结构与稳定性，但随着复垦时间增加，土壤团聚体结构与稳定性均得到提高。土壤各粒径团聚体的C、N及C/N随着复垦时间而增加。>2000μm、250-2000μm和<53μm团聚体的δ13C及>2000μm团聚体的δ15N随复垦年限增加而降低。>2000μm与250-2000μm团聚体中，新C占土壤总C的比例>80%，而在<53μm团聚体中，新C的比例在复垦14～17a间显著增加，此后则变化不显著。平朔矿区复垦年限相同的7个样地中，刺槐—油松林的乔木生物量、年凋落物生物量和未腐殖凋落物生物量、叶片C含量、叶片N含量、250-2000μm和>2000μm的C、N含量最高。不同复垦年限样地中，刺槐林的叶片、凋落物、根系中C和N含量较高，而油松林的N含量较低，C/N比最高。刺槐林中叶片、凋落物和根系的C和N含量随复垦时间减少。土壤C和N含量随复垦年限增加而增加。叶片δ15N也随复垦年限而增加。根据C同位素结果，复垦生态系统C的周转过程为：叶→凋落物/根→土壤大粒径团聚体→土壤微团聚体/黏壤粒。油松可以促进次生刺槐和榆树C的积累，而原生刺槐和榆树竞争关系将导致的C积累少于预期。此外，原生的刺槐和榆树的种内竞争也对树种生物量C积累有负作用。从生态系统多功能（碳固定能力、生物量生产力、生物多样性保护、养分积累）视角看，刺槐—油松林多功能得分要高于其他复垦样地。复垦煤矿生态系统结构和功能在复垦20-23a后，达到了一个区别于原地貌的相对稳定状态。上述研究揭示了矿区复垦土壤团聚体结构恢复过程中土壤碳恢复机理，可为大型露天煤矿生态修复提供理论依据。