Simulation Experiment Research Of The Impacts Of Leaked Carbon Dioxide From Underground On Soil Micro-ecological Environment

The problem of climate warming has attracted global attention.Geological storage of CO₂,as the internationally recognized effective measure for reducing carbon emissions,is expected to become the core technology to deal with global climate change in the future.But the technology is currently in the development stage,it carries a risk of sealed CO₂ leakage due to the complexity of the storage process,which might bring a serious negative impact on human survival and development.Soil microorganism and soil enzyme play an important role in the ecosystem and are closely tied to soil health.Therefore,studying their response mechanism to the elevated CO₂ is the key to comprehensively evaluate the impact of on soil ecological environment,which will provide a very important reference for the actual operation of CO₂ storage projects and implementation of CO₂ emission reduction tasks in China.In this study,an artificial CO₂ release system provided a feasible access to the study of the leaked CO₂ effects on soil microbial environment and surface vegetation.This experiment consists of two parts.In the greenhouse experiment,we have managed to use the viable counting method to identify the amount of soil microbes in three experimental areas?ryegrass,pea and amaranth?with the concentration of 0%,5%,10%,15%?v/v?CO₂,and also analyzed the microbial community structure of soil bacteria and fungi by using the PCR–DGGE fingerprint and 16 S rDNA library technology.In the outdoor barrel cultivated strain experiment,the soil enzyme activities,physicochemical properties and vegetation physiological indicators were tested by related soil analysis methods,Illumina Miseq high-throughput sequencing was used to assess the bacterial diversity,abundance and community structure of two kinds of vegetation soil,maize and ryegrass under different high concentration of CO₂?0%?50%?70%?90%?v/v??so as to reveal the effects of geological storage of CO₂ leakage on soil functions.The results indicated that:?1?The effects of different concentrations of CO₂ on soil microbial population was significantly different,it showed three main trends: increased,decreased,or firstly increased and then decreased.Statistical analysis showed that when CO₂ increased from 0% to 15%,The number of bacteria was: ryegrass experimental area > pea experimental area > amaranth experimental area > bare field experimental area;the fungi number: bare ground experimental area > ryegrass experimental area > amaranth experimental area > pea experimental area;the actinomycetes number: bare field experimental area > amaranth experimental area > ryegrass experimental area > pea experimental area.It can be seen that the growth of soil microorganisms under different concentrations of CO₂ should be competitive,and the difference in competition also depended on the type of vegetation.?2?Different concentrations of CO₂ tends to produce strong impact on the diversity of soil's microbial environment,thus leading to the increase of some original bacteria and fungi or reduction,or disappearance of some other originally existing species,or resulting in some other novel species,though the dominant species may remain constant.By comparing the DGGE electrophoresis fingerprint,6 kinds of sensitive bacteria could be selected.When the CO₂ concentration reached 10%?v/v?,soil bacteria of ryegrass could be used as evaluation index of CO₂ leakage were Thauera aminoaromatica and Nitrospira.When the CO₂ concentration reached 15%?v/v?,soil bacteria of amaranth could be used as evaluation index of CO₂ leakage were Gp6?Aciditerrimonas and Pseudoalteromonas,besides,there was an unique fragment of Pestalosphaeria sp.on the DGGE electrophoresis band of amaranth soil fungi,which disappeared when the CO₂ concentration reached 5%?v/v?.The leakage of the CCS project could be evaluated by monitoring the above-mentioned sensitive bacteria and fungi of vegetation soil in the future.?3?Soil bacterial diversity and richness were related to CO₂ leakage levels.It was observed that the structure and composition of microbial communities were inhibited under moderate and low concentration of CO₂ stress,whereas the reaction of bacterial consortium was significantly different under high and extremely high CO₂ concentrations.Proteobacteria,Bacteroidetes,and Acidobacteria etc.were dominant species of soils.The relative abundance of Bacteroidetes demonstrated a great variability,and a significant increase in relative abundance of Acidobacteria under 70% CO₂ concentration,which might be used as microbial sensitivity index to assess the risks of CO₂ leakage.The microorganism could adapt to the CO₂ stress by changing their structure and composition,but the recovery process was difficult to carry out once the community structure was damaged.?4?Soil enzyme activities were not only subject to a high concentration of CO₂,but also closely related to types of vegetation and many other factors.when CO₂ increased from 0% to 50%,the soil catalase,dehydrogenase,urease and protease activities in maize and pea test areas were increased while the invertase activities in maize areas were decreased.Compare to the other test areas,soil enzyme activities in ryegrass test areas were significantly different,When CO₂ reached 90%?the concentration which leaded crops to death?,it possessed the higher soil oxidoreductase and hydrolase activities.?5?High concentration of CO₂ led to soil pH value decreased while the contents of Ca2+ and Mg2+ increased.The soil's fertility indexes showed a decreasing tendency,which made vegetation showed stress characteristics with plant height significantly declined and leaves became sparse and yellow.By contrast,we found that ryegrass had the higher CO₂ stress tolerance and could survive for a long time than corns and peas.Thus,we could plant peas in the storage areas to predict CO₂ leakage by observing its growth,growth abnormality or death.The correlation analysis indicated that soil fungi and bacteria were negatively correlated with soil pH,soil catalase and dehydrogenase activity showed significant negative correlation with rapidly available N whereas the invertase activity showed significant positive correlation with rapidly available N and P.So we could conclude that changes of soil physical-chemical properties could affect the reproduction and activity of microorganisms.