Effects Of Valerian On Microbial Community Structure And Phosphorus Migration And Transformation In Sediments

As an important part of lake ecological system,the submerged plant can control the phosphorus absorption and the nutrient biological availability for lakes.Particularly,the submerged plant can affect the microbial community structure of sediments by changing physical and chemical conditions to have an impact on the phosphorus migration and transformation in the sediments.In this dissertation,the PLFA and SMT phosphorus analysis approaches are utilized in the field experiment to investigate the influence of the growth stage of the submerged plant(Potamogeton crispus Lassociation,Potamogeton pectinatus L association and mixed group)on the microbial community structure variation and phosphorus migration and transformation.Furthermore,the laboratory experiment is also conducted to investigate the influence of the growth stage and density on the microbial community structure variation and the phosphorus migration and transformation.The main conclusions are stated as follows.(1)It can be seen from the field experiment that root microbes of three submerged plants change dramatically in different growth periods in Hongze lake.The influence on sediment microbial community of growth stage is greater than that of plant association itself.In February,March and May,the sediment microbial similarity is 82.57%,84.51%and 80.23%,respectively.Specifically,the difference of sediment microbial structure between February and March is 67.39%,and the difference between March and May and February and May are 19.00%and 68.41%,respectively.In addition,the growth stage of the submerged plant has a great influence on some environmental factors,such as DO,Eh and pH,which is highly related to sediment microbial community structure variations.Particularly,some characteristic PLFA of G-.anaerobic bacteria、fungi are positively correlated with TOC.Some characteristic PLFA of G-are positively correlated with pH.There is a positive correlation between DO and some characteristic PLFA of actinomycetes、G-,and there is a negative correlation between DO and some characteristic PLFA of G+.The relationships of T and TIME are similar to pH.(2)The sediment phosphorus of three submerged plants changes in the different growth stage in Hongze lake.In the germination stage,early growth stage,vigorous growth stage and decline stage,the total phosphorus of Potamogeton crispus L association,Potamogeton pectinatus L association and mixed group increases firstly,then decreases,and increases at last.The variation trends of inorganic phosphorus and organic phosphorus in Hongze lake are similar and the proportion of inorganic phosphorus in total phosphorus is 50%.The ratio of Fe-P in Potamogeton crispus L association increases in vigorous growth stage,and the ratio in decline stage decreases.The varying rule of Ca-P is opposite.Furthermore,the ratio of Fe-Pin Potamogeton pectinatus L association increases in early growth stage,and the ratio in vigorous growth stage slightly decreases.The similar changing rule can also be seen in mixed group with Potamogeton crispus L association In the growth stage of the submerged plant,the sediment environment promote the transformation from organic phosphorus to organic phosphorus,leading to the increase of Fe-P and the decrease of Ca-P.In the decline stage of the submerged plant,the transformation trend from Fe-P and Al-P to Ca-P can be seen.(3)In the different growth stages of Potamogeton crispus L,the growth of submerged plants can increase the proportion of G+/G-ratio in sediments and the decline and fall of plants can reduce the proportion of G+/G-ratio in sediments.The total PLFA of high density root sediment in stabilization reaches 133.9 ug/g,which is 1.16 times and 1.55 times than that of the middle density and low density root sediment at the same time.Furthermore,the microorganism amount of vertical distribution experimental group is highest at 3-5 cm,which is followed by that of surface.The sediment microbial community difference of Potamogeton crispus L between germination stage and vigorous growth stage,germination stage and decline stage,vigorous growth stage and decline stage are 27.02%,51.32%and 44.24%,respectively.The longer the time spans,the greater the difference it is.(4)The Potamogeton crispus L has influence on the change of the microbial community and all kinds ofphosphorus in sediments,which is mainly affected by the growth stages of Potamogetonrispus L.There is a significantly positive correlation between G" and TP,OP and Ca-P.There can also been seen a significantly positive correlation between fungi,actinomycetes and Ca-P.On the contrary,G+,actinomycetes and fungi are negatively correlated with IP and Fe-P.In addition,the main phosphorus variation areas of Potamogeton crispus L concentrate on the 0 to 6 cm sediment area.In the growth stage of the submerged plant,it can be seen the transformation trend from Fe2+ to Fe3+,resulting in the formation of iron phosphate precipitation.Furthermore,microorganisms can also lead to the transformation from OP to IP,which is similar to the results obtained by field experiment.