Organic Carbon Mineralization,fractionation,and Bacterial Community Characteristics In Response To Warming In Xiao Xingkai Lake Sediments

Although lakes cover only 3.7%of the global land surface area,they distribute and collect large amounts of sedimentary material globally,resulting in a wealth of material,information and intense energy exchange.Sediment is an important component of lake ecosystems,considered to be a sink or source of nutrient cycling and one of the most diverse microbial habitats in the aquatic environment.As one of the largest carbon reservoirs on Earth,sediment organic carbon mineralization is an important component of the Earth’s carbon cycle,and understanding the processes and mechanisms of sediment organic carbon mineralization is essential for predicting the impact of climate change on the global carbon cycle.There is a preponderance of research on soil organic carbon mineralization,but less on sediment organic carbon mineralization,and a comprehensive understanding of the factors that control this process is still lacking.The studies that have been conducted indicate that temperature is one of the most important factors affecting sediment organic carbon mineralization.Organic carbon mineralization is largely microbially driven,with increased temperature enhancing microbial life and thus mineralization,but our understanding of the changes in the structure and diversity of these sediment microbial communities during warming is still limited.In view of this,this paper uses the sediments of Xiao Xingkai Lake as the research object,and analyses the effects of warming on sediment organic carbon CO₂and CH₄ emissions,sediment active organic carbon fractions（microbial biomass carbon,dissolved organic carbon,and easily oxidized organic carbon）and changes in microbial bacterial community structure and diversity through field sampling,indoor incubation tests,and laboratory analysis,using gas chromatography analyzer and 16s high-throughput sequencing technology.The main results are as follows:（1）The CO₂ and CH₄ emission rates of the sediments in Xiao Xingkai Lake under different temperature incubation conditions all gradually decreased with the increase of incubation time and finally stabilized.At the end of incubation,the CO₂ and CH₄emission rates of sediments under the three different temperature conditions remained at low levels.Meanwhile,with the increase in incubation temperature,the sediment CO₂ and CH₄ emission rates and cumulative emissions of the Xiao Xingkai Lake showed an increasing trend.The average CO₂ emission rates were 42.22μg C kg^-1 OC^-1 h^-1（5°C）,46.74μg C kg^-1 OC^-1 h^-1（10°C）,and 66.89μg C kg^-1 OC^-1 h^-1（15°C）during the incubation period,and the cumulative CO₂ emissions were 52.25±0.88 mg C kg^-1 OC^-1（5°C）,58.62±0.54 mg C kg^-1 OC^-1（10°C）,and 75.24±0.11 mg C kg^-1OC^-1（15°C）,respectively.The average emission rates of CH₄ were 0.06μg C kg^-1 OC^-1 h^-1（5°C）,0.07μg C kg^-1 OC^-1 h^-1（10°C）,and 0.08μg C kg^-1 OC^-1 h^-1（15°C）,respectively;the cumulative emissions of CH₄ were 62.95±0.93μg C kg^-1 OC^-1（5°C）,74.50±0.81μg C kg^-1 OC^-1（10°C）and 139.14±1.43μg C kg^-1 OC^-1（15°C）,respectively.This indicates that warming can promote the mineralization of organic carbon in the sediments of Xiao Xingkai Lake.In addition,the Q₁₀ of CO₂ emission from the Xiao Xingkai Lake sediment was 1.50±0.14,while the Q₁₀ of CH₄ emission was 2.31±0.61,indicating that the CH₄ emission from the Xiao Xingkai Lake sediment would be more sensitive to the warming response.In the future,we should pay attention to the sediment CO₂ and CH₄ emissions from Xiao Xingkai Lake.（2）During the mineralization incubation period,the average contents of microbial biomass carbon（MBC）,dissolved organic carbon（DOC）,and easily oxidized organic carbon（EOC）in the sediment varied under the incubation conditions of 5°C,10°C and15°C,but the differences were not significant.However,these organic carbon fractions showed different dynamic patterns under different temperature conditions.Under the condition of 5℃,the variation of MBC and DOC contents significantly affected the sediment CO₂ and CH₄ emission rates,which increased significantly with their increase;while the variation of EOC contents had less effect on sediment CO₂ and CH₄ emissions.However,the effects of the changes in MBC and DOC contents on sediment CO₂ and CH₄ emission rates were not significant at 10°C and 15°C.This may be because the effects of MBC and DOC contents on sediment CO₂ and CH₄ emissions diminished with increasing temperature and were no longer important factors affecting the changes in CO₂ and CH₄ emissions.Overall,the sediment MBC,DOC,and EOC contents have different degrees of influence on CO₂ and CH₄ emission rates,and this influence changes with temperature.Therefore,a combination of temperature and changes in the content of different organic carbon fractions is needed to obtain more accurate results when assessing the factors affecting sediment CO₂ and CH₄ emission rates.（3）The characteristics of the sediment bacterial community changed with increasing temperature.The number of specific taxonomic units（ASVs）was positively correlated with temperature,suggesting that warming had an effect on sediment bacterial community composition.Temperature increase led to changes in the relative abundance of different bacterial taxa,with some species gaining dominance while others may decrease or even disappear,thus changing the composition and structure of sediment bacterial communities.In addition,theαandβdiversity of sediment bacterial communities also differed significantly under different temperature incubation conditions,indicating that warming also had an effect on bacterial community diversity.By studying the symbiotic network of sediment bacterial communities,we found that the network complexity of sediment bacterial communities also changed under different temperature conditions,and may be accompanied by changes in some key species.This suggests that warming not only changes the composition and diversity of sediment bacterial communities but also affects the interaction relationships and strength of sediment bacterial communities.In summary,the effect of warming on sediment bacterial communities is multifaceted.It changes the composition and structure of sediment bacterial communities and affects community diversity and interactions,all of which may have an impact on the intensity of sediment organic carbon mineralization.Therefore,to help better understand the mechanisms of warming effects on sediment organic carbon mineralization,we need to further understand the effects of warming on sediment bacterial communities.