Impact of Elevated CO2 on Microbial Communities and Functions in Riparian Sediments
The impact of elevated CO2 on microorganisms is one of the focal points for studying the environmental effects of global climate change. A growing number of studies have demonstrated the importance of the direct effects of elevated CO2 on microorganisms, which are confounded by indirect effects and not easily identified. Riparian zones have become key zones for identifying the environmental effects of global climate change due to their special location. However, the direct effects of elevated CO2 on microbial activity and function in riparian zone sediments, especially in polluted riparian zones, are currently unclear. In this study, three riparian sediments with different pollution risk levels of heavy metals and nutrients, MLW (high pollution risk levels of both heavy metals and nutrients), GH (high pollution risk levels of heavy metals and moderate pollution risk levels of nutrients), and YYS (moderate pollution risk levels of both heavy metals and nutrients), were selected to explore the direct response of microbial communities and functions to elevated CO2 excluding plants. The results showed that the short-term effects of elevated CO2 did not change the diversity of bacterial and fungal communities, but altered the composition of their communities. In addition, there were differences in the response of microbial functions to elevated CO2 in three regions. Elevated CO2 promoted the activities of nitrification and denitrification enzymes and led to significant increases in N2O releasing in three sediments, with the greatest increase of 76.09% was observed in YYS. Microbial carbon metabolism function was promoted by eCO2 in YYS, but significantly inhibited by elevated CO2 in GH and MLW. Moreover, TOC, TN and Pb contents were identified as key factors contributing to the different microbial response to elevated CO2 in sediments with different heavy mental and nutrients polluted. In conclusion, this study provided deeper insights into understanding the response of bacteria and fungi in polluted riparian sediments to elevated CO2, which helps to elucidate the complex interactions between microbial activity and environmental stressors.