Study On The Response Mechanism Of The Distribution Characteristics Of Plankton Fatty Acids With The Heterogeneity Of Nutrient Pattern In Reservoirs At Guizhou Plateau

Fatty acids are widely present in animals,plants and microorganisms which are in important of basis for energy and material flow in ecosystems.The different nutritional status of the reservoirs will not only affect the composition of fatty acids synthesized by plankton or obtained from other source,but also significantly affect the transfer of fatty acids from the primary producer phytoplankton to the primary consumer zooplankton.Retained by primary consumer zooplankton,fatty acids are therefore important biomarkers to identify food sources.In order to understand the response mechanism of the heterogeneity of the nutrient pattern of reservoirs in the Guizhou with the distribution characteristics of plankton fatty acids,the location including research on Chayuan reservoir,Wanfeng reservoir,Goupitan reservoir,Langou reservoir,Puding reservoir,Huaxi reservoir,Hailong reservoir and Guijiahu reservoir were sampled 4 times in October 2020,April,June and August 2021,respectively.The community structureof phytoplankton and zooplankton was clarified through the variation characteristics under different trophic states.The relationship was analyzed between phytoplankton and zooplankton with fatty acids.The main conclusions of the study are as follows:Total of There 18 fatty acid were analysed in the sample from 8reservoirs.The dot plot results indicated that the range of fatty acid C16:0and C18:0 of phytoplankton and zooplankton in the eight reservoirs was the largest at different sampling times.About phytoplankton,the C16:0was ranged from 0.61 mg·g^-1(Puding reservoir)to 20.52 mg·g^-1(Wanfeng reservoir),the C18:0 was ranged from 0.32 mg·g^-1(Puding reservoir)to8.46 mg·g^-1(Wanfeng reservoir).About zooplankton,the C16:0 was ranged in 0.31 mg·g^-1(Wanfeng reservoir)to 13.46 mg·g^-1(Guijiahu reservoir),the C18:0 was ranged in 0.15 mg·g^-1(Wanfeng reservoir)to 5.57 mg·g^-1(Hailong reservoir).The difference was that the content of fatty acid C18:1n9 in phytoplankton fluctuates at different sampling times and in different reservoirs,the C18:1n9 was ranged in 0.41 mg·g^-1(Chayuan reservoir)to5.57 mg·g^-1(Wanfeng reservoir).The content of C20:4,C20:5 and C22:6 in zooplankton fluctuates in the range,C20:4 was ranged in 0.071 mg·g^-1(Chayuan reservoir)to 5.29 mg·g^-1(Guijiahu reservoir),C20:5 was ranged in 0.093 mg·g^-1(Chayuan reservoir)to 6.23 mg·g^-1(Huaxi reservoir),C22:6was ranged in 0.087 mg·g^-1(Chayuan reservoir)to 4.38 mg·g^-1(Huaxi reservoir).Through PCA principal component analysis,the environmental factors among TN,TP,DO,WT,SD,Chl.a,COD_Mn and p H were the main environmental factors with 14 factors.The T test results showed that TN,COD_Mn,SD,and Chl.a had great differences.The phytoplankton community structure showed that the cell densities of Chlorophyta and Bacillariophyta were higher than those of phyla,and the biomass among Chlorophyta,Bacillariophyta and Pyrrophyta were higher than other phyla in the poor-neutrophic state.The phytoplankton community structure had influenced by TN,TP,COD_Mn,SD,WT and DO,and the main dominant algal species were both Cyanophyta and Bacillariophyta(Scenedesmus bijuga,Cyclotella sp.,Navicula sp.,and Cryptomonas sp.)in eutrophic and mildly eutrophic states.In the medium eutrophic state and mild eutrophic state,the cell density of Bacillariophyta and Pyrrophyta was higher,and the biomass of Bacillariophyta and Pyrrophyta is dominant.In the medium eutrophic state,the main dominant algal species Synedra ulna,Peridinium sp.and Ceratium sp.The main dominant algal species in the reservoirs were Pseudanabaena sp.,Synedra ulna,Cosmarium sp.and Cyclotella sp.The community structure was influced by TP,COD_Mn.Chl.a,SD,WT,p H in medium eutrophic state.However,in mild eutrophic state,the community structure depended TP,Chl.a,WT and DO.According to the result,zooplanton in the nutrient-poor state,the density and biomass were dominated by copepods and rotifers.The main influencing factors were TP,SD,WT and DO,and the main dominant species were Keratella cochlearis and Keratella valga.In the medium eutrophic state,the density of rotifers was the largest,and the biomass value of copepods was the highest.The main dominant species were Keratella cochlearis,Keratella valga,etc.In mild eutrophic state,the copepods of density was higher than that of species,and copepods and rotifers had the highest biomass.The main dominant species were Keratella cochlearis and Brachionus forficula.In the three nutritional states,the concentration of fatty acid SFA in phytoplankton was higher than MUFA and PUFA.The content of MUFA was the highest in the nutrient-poor state,followed by mild eutrophication,and the lowest content found in the medium eutrophic state.The concentration of SFA in metazooplankton at mild eutrophic state was lower than nutrient-poor state and medium eutrophic state.The MUFA and PUFA had the highest content in medium eutrophic state,followed by mild eutrophication,and the lowest content was in poor and moderate eutrophic state.Phytoplankton fatty acids were divided into five categories in the nutrient-poor state,the first category was C16:0,the second category was C18:0,the third category was C20:3n6,the fourth category included C16:1,C14:0 and C18:1n9,the fifth category included the rest of 12 types.In the eutrophic state,fatty acids were divided into five categories,the first and second categories were the same as the nutrient-poor classification,the third category was C18:1n9,the fourth category was C16:1,the fifth category included the rest of 14 types.In mild eutrophic state,fatty acids were divided into four categories,the first and second categories were the same as the nutrient-poor classification,the third category included C14:0,C16:1,C18:1n9 and C18:2n6,the fourth category included the rest of 12types,Zooplankton fatty acids had the same categories as phytoplankton in categories in the first and second category the nutrient-poor state,the third category was C18:2n6,the fourth category includes C18:1n9 and C18:3n3,and the fifth category includes C16:1,the sixth category included the rest of 12 types.In the eutrophic state,fatty acids can be divided into six categories,the first category was C16:0,the second category was C16:1,the third category was C20:4,the fourth category includes C20:5 and C22:6,and the fifth category includes C18:1n9,C18:3n3?C18:2n6,the sixth category included the rest of 11 types.In mild eutrophic state,fatty acids were divided into four categories,the first category was C16:0,the second category was C18:0,the third category was C20:5,the fourth category included the rest of 15 types.During the mild eutrophic state,the DHA in phytoplankton was significantly positively correlated with it in zooplankton,indicating that the fatty acid DHA required by zooplankton mainly came from the DHA from phytoplankton.The EPA of zooplankton was significantly positively correlated with DHA from phytoplankton.Copepods had an active enzymatic mechanism that could reduce the saturation of EPA and prolong EPA to DHA.