Effects Of Temperature And CO₂Concentrations On The Periphyton Biofilm

Periphyton biofilm is a semi-stable, opened microecosystem composed of a single ormixed microbial populations which is growing development activity，it can truly reflect thewater quality of the environment and the value of the ecosystem services. By simulationexperiments, this study trys to investigate the effects of the temperature or the CO₂concentration change on the periphyton biofilm in the point of view of microbial ecology bycharacterizing the enzymatic activity of the periphyton biofilm and extracellular polymers.The results are theoretically helpful for us to undstand the effects of climate change onecosystem by periphyton biofilm. The results showed as follows:The effect of temperature on the periphyton biofilms: Compared with the control, in theprocess of temperature change, the algae in the periphyton biofilm were rarely, while bacteriawere abundant. In the whole process, the DHA of the periphyton biofilms was alwaysfluctuating at low level. The fluctuation of the temperature significantly changed itspolysaccharide content of the EPS of the periphyton biofilms, but it had no significant effecton the protein content. As the temperature rising, it promoted the microbial activity and theutilization rates of carbon source of the periphyton biofilm, especially for carbohydrates,carboxylic acids, polymers, phenolic acid and amine, compared to the control group; At thisstage the bacterial community structure changed significantly and its stability was poor; Thesimilarity of the community structure diversity was lowest （only13.6%）, it’s lower than thecontrol group. As the temperature falling, the microbial activity decreased, utilization rates ofcarbon sources also significantly decreased, but the lowest similarity （39%） was higher thanthe lowest in the stage of the temperature rising; thus, during this stage, the communitystructure is more stable.The effect of CO₂concentrations on the periphyton biofilms: Compared with the control,in the process of CO₂concentrations change, the dominant species of the periphyton biofilmhad changed from algae to bacteria. In the whole process, the DHA of the periphyton biofilmswas always maintained at low level. The fluctuation of the CO₂concentrations significantlychanged its protein content in the EPS of the periphyton biofilms, but it had no significanteffect on the polysaccharide content. As the CO₂concentration rising, it promoted themicrobial activity and the utilization rates of carbon source of the periophyton biofilm; At thisstage the bacterial community structure changed significantly and the stability was poor; Thelowest similarity of the community structure diversity was only22.6%, lower than the controlgroup; As the CO₂concentration falling, the microbial activity decreased, utilization rates of carbon sources also significantly decreased, but the lowest similarity （44.9%） was higher thanthe lowest in the stage of the CO₂concentration rising; thus, the community structure is morestable during this stage.Finally, the effects of the temperature or the CO₂on the periphyton biofim are similar;When the temperature and CO₂concentrations increase to a threshold （35℃,0.9%）, theenzyme activity, the content of polysaccharide and protein of the EPS had significantlychanged compared with the control. The stability of the community structure diversity in thefalling stage was higher than that in the rising stage whatever the temperature or the CO₂concentrations.