Plant traits interacting with sediment properties regulate sediment microbial composition under different aquatic DIC levels caused by rising atmospheric CO2

Abstract

Rising atmospheric CO2 causes an increase in dissolved inorganic carbon (DIC) availability in aquatic ecosystems, further affecting plant growth and aquatic ecosystem production. Belowground carbon input can strongly influence microbial processes (carbon or nitrogen cycling). However, changes in sediment microbial abundance and community structure have not been thoroughly assessed in freshwater ecosystems under rising atmospheric CO2. A pot experiment was conducted using fragments of the submerged macrophyte Myriophyllum spicatum L. to study plant and sediment microbial responses to increasing aquatic carbon availability under rising atmospheric CO2. Three DIC levels of overlying water were set up by continuous bubbling with different concentrations of CO2. Higher biomass accumulation, chlorophyll content, nitrate reductase activity, and leaf N content were observed in M. spicatum under high DIC level in CO2 treatment. The increased DIC level in CO2 treatment reduced sediment ammonium nitrogen, dissolved organic nitrogen content, microbial biomass carbon content and phenol oxidase activity, but not microbial biomass nitrogen content, urease and N-acetyl-β-D-glucosaminidase activities. NifH abundance significantly decreased with the increasing DIC levels in CO2 treatment, while bacterial 16S rRNA abundance was not affected. Redundancy analysis results indicated a modest but obvious shift in sediment microbial community compositions among different levels of DIC. Variation partitioning revealed a strong interaction between plant traits and sediment properties and their regulation of sediment microbial compositions at different DIC levels. It seemed that an intensified competition for essential resources between M. spicatum and sediment microbes occurred under increased aquatic DIC availability caused by rising atmospheric CO2.