The Research Of Interaction Mechanisms Between Plant-Sediment Microbial System And Nutrient Elements In The Wuchang Lake

The distribution of large emergent macrophytes in eutrophic state will lead to differences in ecological functions between macrophyte-dominated areas and macrophyte-free areas.Understanding the environmental fragility and nutrient cycling pathways of macrophyte-dominated areas and macrophyte-free areas is helpful for the formulation of lake ecological restoration plans.This study takes Wuchang Lake,a typical macrophyte-type lake,as the research object,which is a heavily eutrophic lake.First,elemental analysis and synchrotron radiation technology were used to determine the composition and occurrence form of sediment nutrients.Secondly,the sources of nitrogen in water and sediment were analyzed through the fractionation effect of nitrate nitrogen and oxygen isotopes.Further,based on high-throughput sequencing,metagenomics and metabolomics technology to explore the spatial distribution characteristics of sediment microorganisms and the driving mechanism of macrophytes for their assembly process,and clarify the transformation paths of carbon,nitrogen and phosphorus in macrophyte-dominated areas and macrophyte-free areas,and reveal the interaction mechanism of macrophyte and sediment-microbial systems.The main findings are as follows:（1）Compared with the macrophyte-free area,the macroemergent macrophytes in the macrophyte-dominated area increased the content of organic matter（average increase of 2.22 g/kg）and total nitrogen（average increase of 41.58 mg/kg）in the sediment,and were beneficial to the enrichment of iron phosphate（increase of 13%）.OM and TN were mainly derived from macrophyte litters and showed a significant positive correlation（p<0.05）.The nitrogen uptake by macrophytes and release from litters caused a positive shift of δ¹⁵N-NO₃^-by 4.21‰ and a positive shift of δ¹⁸O-NO₃^-by 8.78‰.However,the increase in the relative content of FePO4 was mainly due to the effect of macrophyte roots on it,rather than macrophyte litter.（2）OM and TN drive changes in bacterial community structure,assembly process,and stability in macrophyte area sediments.Compared with macrophytefree areas,dominant species such as Proteobacteria and Chloroflexi showed more significantly correlated with OM and TN in macrophyte-dominated areas.In terms of phylogenetic turnover rate,the macrophyte-dominated area（88.9%）was significantly larger than the macrophyte-free area（12.3%）,and with the increase of the TN concentration difference,the bacterial assembly process in the surface sediments changed from stochastic to determinate.The mean degree（41.75）,graph density（0.049）and clustering coefficient（0.557）of the bacterial community cooccurrence network in the sediments of the macrophyte-dominated area were significantly higher than those of the macrophyte-free area（4.01,0.009 and 0.359）,but the bacterial community in the macrophyte-free area was stable（0.72）than that of macrophyte-dominated area（0.63）,mainly due to high deterministic phylogenetic turnover and nutrient（TN and OM）concentrations that reduced community stability in macrophyte-dominated area.（3）The macrophyte-microbe system enhanced the conversion of nitrogen and phosphorus to bioavailable forms and reduced methane emissions and root suppression risk.In addition to the enrichment of nitrification and denitrification functional genes in the rhizosphere,the abundance of genes for nitrate reduction to NH₄⁺ was significantly increased.The gene abundances of phnW,phoA and phoD encoding alkaline phosphatase in the macrophyte-dominated areas were higher than those in the macrophyte-free area,and the abundance of the gcd gene that facilitated the dissolution of insoluble inorganic phosphorus in the rhizosphere region was significantly greater than that in the root-free area.The microorganisms in the rhizosphere have weak methane production ability but strong methane oxidation ability and can metabolize formaldehyde at the same time.A large number of organic acids secreted by macrophyte roots lowered the pH of rhizosphere sediments,which in turn induced the mutualistic symbiosis of the Acidobacteria,which produce NH₄⁺,increase phosphorus,and prevent root suppression.