Effects Of Typical Submerged Plants On Microbial Community Structure And Phosphorus Forms In Sediments

Being the important structural component of lake ecosystem, submerged macrophytes are believed to greatly influence nutrient cycling in sediments, which is closely related to the lake eutrophication. Sediment microorganism are important drivers of sediment processes, and play a key role in elemental cycling. Therefore, studying the effects of submerged macrophytes on-microbial community structure and phosphorus forms in the rhizosphere sediments could further reveal the environmental effects of submerged macrophytes, and provide theoretical support for ecological restoration in lakes.Microbial phospholipid fatty acids (PLFAs) was employed to analyze the sedimentary microbial community structure in naturally distributed communities of Potamogenton malaianus, Potamogeton crispus and Vallisneria natans in Taihu Lake and Hongze Lake and phosphorous fractions were studied at the same time Microcosm experiments had been conducted with the collected sediments and plants to verify the impact mechanism and action principle of submerged macrophytes on environmental factors, microbial community structure and phosphorous forms. Results were as follows:(1) Field investigation showed that significant variation in sedimentary microbial community structure existed among cites of different submerged macrophytes species. The calculated diversity between that of P.malaianus and P.crispus was 38.23%, between that of P. malaianus and V.natanswas 81.53%, while between that of P.crispus and V.natans reached 78.61%. Principle component analysis (PCA) analysis showed that temperature and redox potential are two main factors affecting microbial community structure.(2)The contents of phosphorous forms in sediments were found highly varied among different communities of macrophytes species. Total phosphorus (TP), organic phosphorus (OP), inorganic phosphorus (IP) in P.malaianus-planted sediment was higher than that of P.crispus and V.natans. In the sediment from P.malaianus community, the content of phosphorus extraction by HCl accounted for 50%-78% of inorganic phosphorus, while in sediments with P.crispus and V.natans, phosphorus extraction by HCl accounted for 35% and 32% of inorganic phosphorus respectively.(3)As the growth of V.natans, The calculated diversity between that of initial stage of growth and exuberant period was 23.63%, between that of initial stage of growth and decline phase was 38.71%, while between that of exuberant period and decline phase reached 37.69%. Principle component analysis (PCA) analysis showed that temperature, pH, redox potential are main factors affecting microbial community structure. The relative content of gram-positive bacteria increased by 9.22%at day 185 of cultivation, while the relative content of gram-negative bacteria reduced by 7.98%, and the relative content of fungi increased by 4.23%. Total content of PLFA in sediments increased by 60.17%. Total content of PLFA in sediments and microbial activity was significantly positively correlated. However, total content of PLFA was significantly negatively correlated with total phosphorus content, indicating the fundamental impact of microorganisms on transportation and transformation of phosphorus in lake sediments.(4)The growth of V.natans could significantly reduce the content of organic matters and phosphorous in sediments. At day 185 of cultivation (decomposition period), the content of TP, OP and IP in surficial sediments were reduced by 8.97%, 7.8% and 10.28%. Vertically, due to the flourish root at top 2-5cm of the sediment, contents of various forms of phosphorus were lowest in the top layer.