通过模拟高浓度CO_2在农田土壤中的地下泄漏,研究了不同浓度CO_2泄漏情景下土壤微生物多样性的变化。实验设置了400 g m~(-2) d~(-1)、800 g m~(-2) d~(-1)、1 200 g m~(-2) d~(-1)和2 000 g m~(-2) d~(-1)持续CO_2通气60 d共计4个处理,并与对照组、恢复组(2 000 g m~(-2) d~(-1)组停止通气60 d后)分期采集土壤样品,分析土壤理化性质、土壤闭蓄的气体浓度、微生物多样性指数及主要类群变化规律。结果表明,4种处理均提高了土壤中CO_2浓度,分别为1.60%、4.80%、10.80%和19.60%。土壤微生物多样性Chao指数和Shannon指数随CO_2通入量增加而减少,降幅分别达17.00%~27.80%和6.10%~9.50%。相反,非度量多维尺度(NMDS)分析显示土壤微生物beta多样性在中、低浓度升高,在高、极端浓度表现为降低。拟杆菌属(Bacteroidales)相对丰度随CO_2泄漏量增加从3.09%上升至21.20%,可作为高浓度CO_2泄漏生态安全性评估的敏感性指标。基于高通量序列相似度OTU分类的RDA分析表明土壤环境因子的变化能够较好地解释微生物多样性演替。研究结果为评估和监测地下CO_2泄漏对近地表生态系统环境风险提供科学依据。
英文摘要:
【Objective】 To cope with the trend of global warming, CO_2 capture and storage (CCS) is one of the major technologies for reduction of CO_2 emission. And then the captured CO_2, nil in commercial value, is injected underground to raise the output of petroleum or coalbed methane, so as to maximize its economic profit. However, the prevailing technologies are far from being capable of guaranteeing zero leakage of the stored CO_2 during the processes of CO_2 storage and transportation, geological activities and human misoperation. Once the risk of potential CO_2 leakage becomes real, the leakage will pose an enormous threat to the near surface ecosystem. It is, therefore, essential to explore in depth effects of underground CO_2 leakage on farmland soil environment, especially tolerance and sensitivity of soil microbial communities to different concentrations of CO_2. So the study was conducted.【Method】 An experimental platform to simulate underground CO_2 leakage was constructed in an idle farmland, in the South Lake Campus of the China University of Mining and Technology. The platform was used to simulate leakage of CO_2 varying in intensity, i.e.400 g m~(-2) d~(-1), 800 g m~(-2) d~(-1), 1 200 g m~(-2) d~(-1) and 2 000 g m~(-2) d~(-1) for 60 days, thus forming four treatments, i.e. L-400,M-800, H-1200 and E-2000. Besides, the experiment also had a control group and a recovery group. Soil samples were collected from the four treatments and their 3 replicates on the 14th, 30th and 60th day after the start of simulated leakage, from the control group on the day before the start of leakage (C1) and at the end of the experiment (C2), and from the recovery group, which was actually Treatment E2000, 60 days after the stop of the leakage. The soil samples were analyzed for soil physical and chemical properties, concentration of occluded soil, structure and alpha and beta diversities of soil microbial community with the conventional physicochemical analysis method and the Illumna second generation gene sequencing method based on the Miseq platform.【Result】 Results show that CO_2 leakage decreased soil pH, electrical conductivity and nitrate nitrogen content and the effect was enhanced with rising CO_2 concentration whereas it had an opposite effect on soil organic matter content. In all the four treatments. Soil CO_2 concentration increased till it reached saturation in 24 h, when soil CO_2 gas concentration leveled off at 1.60%, 4.80%, 10.80% and 19.60%, respectively. Along with increasing CO_2 flux, soil microbial community decreased in diversity, Chao index and Shannon index, by 17.00% ~27.80% and 6.10% ~9.50%, respectively. In contrast, soil microbial community increased in beta diversity (NMDS index) in Treatments L-400 and M-800 (low CO_2 concentration) but decreased in Treatments H-1200 and E-2000. Some bacteria, like Bacteroidales, varied extremely, either rising up or falling down in relative abundance with increasing CO_2 leakage. 【Conclusion】 The structure, diversity and abundance of soil microbial community varied significantly from treatment to treatment. Soil pH and CO_2 flux were the two most important environmental factors affecting soil microbial diversity. Bacteroidales was very sensitive to CO_2 stress so that it can be used as a key indicator in monitoring and evaluating ecological risk of underground CO_2 leakage. The 60 d short term recovery experiment indicates that the soil microbial community recovered well in diversity and richness, but it is still unclear whether it did in function. Therefore, in future studies, focuses should be laid on impacts of underground high concentration CO_2 leakage on functions of the soil ecosystem.