A Comparative Study Of Impact Of Different Carbon Source On Benthic Microbial Community Structure Between Macrophytes-and Algae-dominated Areas In Taihu Lake

The East Lake Taihu and Meiliang bay are respectively characterized by highdensities of submerged macrophyte and phytoplankton which has an important effecton the structures and functions of microbial food webs. Analysis of phospholipid fattyacids (PLFAs) were used for the investigation of benthic microbial community in thesediments of lakes or areas dominated by submerged macrophytes and algae. Theresults showed that:(1) The decline trend of microbial biomass and diversity invertical was found in the submerged macrophytes-dominated and algae-dominatedsediment. Redundancy analysis (RDA) showed that TOC, TN, TP, Chl a were themain factors differentiating samples from surface sediment and bottom sediment inthe Meiliang Bay, thus accounting for the vertical variation in the algae-dominatedsediment.(2) Higher concentrations of total PLFAs, indicator of microbial biomass,were found in the Meiliang Bay. RDA indicated that pH was positively correlatedwith benthic microbial community stuctures in the submergedmacrophytes-dominated zone, but manifested negative relation with that in thealgae-dominated zone. Thus, pH was the driving force controlling the variation ofmicrobial community structures between the submerged macrophytes-dominated zoneand the algae-dominated zone.(3) The relative abundances of bacteria were higher atthe sediment surface than deeper depth. A large amount of18:2ω6and20:4ω6,respectively biomarker of fungi and protozoa, was found at the surface sediment,implying the impacts of resource availability and predation pressure on the bacterialrelative abundance.To investigate the impact of carbon source on the benthic bacterial communityfurther, we constructed microcosms with six treatments. Macrophyte sedimentsystems: macrophyte sediment as control; macrophyte sediment+Vallisneria natansdetritus; macrophyte sediment+Microcystis detritus; Algae sediment systems: algaesediment as control; algae sediment+Vallisneria natans detritus; algaesediment+Microcystis detritus. The results showed that the consumption of resources in the algae systems were greater than macrophyte systems, which suggested higherlevel of bacterial productivity in the algae-dominated zone. Furthermore, a greateramount of resources were consumed in the treatments with addition of Microcystisdetritus, which illustrated that Microcystis detritus had a stronger stimulatory effect onthe bacterial productivity than Vallisneria natans detritus. Principal coordinateanalysis (PCoA) and cluster analysis indicated that bacterial community in themacrophyte systems performed better stability with addition of detritus.Proteobacteria was the predominant species in all treatments, the relative abundanceof which ranged from30.8%to54.3%. However, the relative abundance ofProteobacteria in the treatments from the algae systems was more than those from themacrophyte systems. This implies that Proteobacteria is inclined to uptakeMicrocysitis detritus to support their growth. In conclusion, the researchesdemonstrated that benthic microbial community was associated with the quantity andquality of carbon source, and environmental factors as well.