Aquatic microalgal and bacterial communities in a karst wetland watershed

Abstract

Microalgal abundance and community composition are important aspects impacting carbon sequestration in aquatic karst ecosystems. At present the relationship between Ca2+ and HCO3− concentrations and microalgal communities specifically in aquatic karst environments is not well understood. In this study, the microalgal and bacterial community structures were investigated in the aquatic karst environments with different Ca2+ and HCO3− concentrations in a watershed of the Huixian karst wetland, Guilin, China. Community analysis was based on the use of Illumina sequencing of 23S rRNA and 16S rRNA genes, respectively. The results showed that eukaryotic microalgae were dominant at sites with high concentrations of HCO3− and Ca2+, while cyanobacteria were the major microalgae at sites with low concentrations of HCO3− and Ca2+. Cyanobium was the most dominant Cyanobacterial genus with a relatively high abundance in karst water samples. The microalgal community was affected by the concentrations of Ca2+ and HCO3−, nitrogen sources (concentrations of ammonium and nitrate especially), and bacterial diversity and community composition. Flavobacteriia and Gammaproteobacteria were the major bacterial classes associated with microalgae. The water carbonic anhydrase (CA) activity was significantly positively correlated with the relative abundance of Chlorella, which was the dominant genus in the microalgal community. The data suggest that Chlorella may play a leading role in CA activity and carbon stabilization capacity of microalgal communities in this aquatic karst ecosystem.