Microbial Carbon Fixation Rate And Control Factors In Tengchong Hot Spring

The CO₂ emission of volcanic terrestrial hot springs is an important source of the earth's natural emission of greenhouse gases,and it also provides a sufficient carbon source for the metabolism of hot spring microorganisms.However,the previous geologists and meteorologists paid more attention to the geological process,while ignored the role of microorganisms in carbon emission.Thermophilic autotrophic microorganisms,as primary producers of volcanic geothermal ecosystem,assimilate inorganic carbon into organic carbon through photoautotrophy using light energy and chemoautotrophy using the reducing gas H₂ and the reducing ions S^2-,Fe²⁺,NO₂^-,which control the mutual transformation of inorganic carbon and organic carbon,affect the surface carbon cycle,and promote the biogeochemical cycle of other elements.Therefore,clarifying the flux of autotrophic microorganisms converting inorganic carbon into organic carbon,and studying the response relationship between carbon fixation capacity of hot spring microorganisms and environmental factors will help us to understand the process and mechanism of carbon cycle of hot spring ecosystem,to understand the carbon budget in global volcanic regions,and to provide theoretical basis for accurate estimation of greenhouse gas emissions basis.In this study,we selected the geothermal pool in Tengchong Volcano Geothermal National Geopark,Yunnan Province,which has similar physical and chemical parameters except the temperature gradient(69?75?).Through in-situ culture of Na H¹³CO₃ and 16S r RNA high-throughput sequencing technology,we explore the carbon fixation ability and community structure of photosynthetic autotrophic microorganisms in hot springs at different temperatures.In addition,seven hot springs with different and irregular physical and chemical parameters were selected to explore the carbon fixation capacity and community structure of chemoautotrophic microorganisms in hot springs,and discusse the energy sources and influencing factors of carbon from the perspective of genome by in-situ culture of Na H¹³CO₃ and metagenomic sequencing technology.The results showed that the carbon fixation capacity of photosynthetic autotrophic microorganisms decreased with the increase of temperature.The highest carbon fixation rate was about 4637?g C/g TOC/h at the lowest temperature(69?),and the lowest carbon sequestration rate was about 138?g C/g TOC/h at the highest temperature(75?).Its carbon fixation capacity is more significant in the daytime.Based on the previous measurement data of the average temperature and CO₂ emissions of the geothermal pool,we estimate that microorganisms can fix80%of the CO₂ emitted in the daytime as organic carbon.And the photosynthetic carbon fixation rate in the daytime and respiration rate in the night have a negative exponential correlation with temperature,as that the activities of related enzymes decrease after exceeding the optimum temperature and temperature has a negative effect on Photosynthetic components in cells.The ability of carbon fixation of chemoautotrophic microorganisms in hot springs is far lower than that of photosynthesis,and it will be limited by light for ultraviolet radiation in visible light has a negative impact on microbial metabolism.The main chemoautotrophic microorganisms are distributed in thermoproteota phylum,and reducing tricarboxylic acid cycle is the most widely distributed chemoautotrophic carbon fixation pathway in hot spring microbial community,and its energy source the oxidation of H₂ and S^2-.The above results reveal the response relationship between the carbon fixation capacity of hot spring microorganisms and environmental factors,which is helpful to deeply understand the carbon cycle process of hot spring system,to comprehensively understand the carbon budget of hot spring ecosystem in global volcanic regions,and to provide theoretical basis for accurately estimating the geological emission of greenhouse gases.