The Simulation Of The Decomposition Processes Of Carex Cinerascens And Phalaris Arundinacea And The Dynamics Of Bacterial Community Under Flooding Stress

The litter decomposition of plants is an important part of the material cycle and energy flow of wetland ecosystems.Due to the unique hydrological characteristics of Poyang Lake,the decomposition process of plants in Poyang Lakes is different from other wetlands.To reveal the differences in the decomposition process of living plants and natural litters in Poyang Lake wetland under flooding stress,two dominant species(Carex cinerascens and Phalaris arundinacea)were selected to conduct the simulation experiment via litter bag method.The fresh and dried plant samples were used to simulate the decomposition processes of living plants and natural litters,respectively.The plant decomposition rate and nutrient release dynamics were monitored.Simultaneously,the dynamic changes of microbial community structure during plant decomposition were explored after the process of 16 S rRNA gene high-throughput sequencing and q-PCR.The main results are as follows:(1)In the 180 d flooding experiment,it was found that the living plants and natural litters of both plants(C.cinerascens and P.arundinacea)showed similar decomposition regularity.Specifically,the decomposition of the early stage is faster and the later stage is slow.But the living P.arundinacea decomposed faster than its litters,while living C.cinerascens decomposed slower than its litters.(2)During the early stage(i.e.,before 30d)of the decomposition process,the activities of the four hydrolases(Bglu,Bxyl,NAG and Phos)of the two living plants were significantly higher than those litters,indicating that sufficient water in the living plants favored the microorganisms' growth,reproduction,and the enzyme activity.On the 60 d,the available energy substances cannot satisfy the growth of microorganisms.Thus,the microbial biomass was reduced,and the enzyme activity was significantly reduced.(3)The abundance of microorganisms in the early stages of the decomposition process was significantly higher than other stages.The microbial diversity index showed the trend of increasing first and then decreasing,reaching the highest value during the mid-decomposition.There are seven main types of microbial community composition(accounting for >1%),Proteobacteria,Firmicutes,Actinobacteria,Acidobacteria,Bacteroidetes,Chloroflexi,Spirochaetae,where the Proteobacteria(66.28%)is the dominant flora.(4)The plants released a large amount of nutrients into the environment under the flooding stress.And the dynamic changes of TOC,TN and TP content in the water were basically the same: showing a trend of increasing first and then decreasing.The nutrient concentration was highest at the 30 th day,and then tended to be stable.The slow decrease in concentration tends to be stable.The gradual increase of pH in water is the main factor affecting the bacterial community structure.At the end of the experiment,the contents of TOC,TN and TP in the sediment did not increase significantly.Besides this,the changes in nutrient content in the sediment did not have a significant effect on the microbial community structure.Therefore,nutrients released during plant decomposition may be utilized by microorganisms or enter the atmosphere in the form of gases.In summary,the physical and chemical properties,extracellular enzyme activities,microbial abundance and bacterial community structure of living plants and litters in wetlands under flooding stress show significant differences.In the early decomposition process,the plant decomposition rate is faster,and the amount of released TOC,TN and TP nutrients are large.The nutrient content in the overlying water increases rapidly,the microbial abundance is high,and the extracellular enzyme activity is high.In the later stage of decomposition,the decomposition rate of plants is slow,and it is unable to provide the energy substances required for the growth of microorganisms,and the abundance of microorganisms is significantly reduced.The microbial diversity index shows a trend of increasing first and then decreasing.In the decomposition process,the species richness gradually increases,and the microbial community structure in the mid-decomposition period tends to be complex.At the end of the decomposition experiment,there are no significant increase in carbon,nitrogen,and phosphorus in the soil,indicating that part of the nutrients released by plant decomposition are absorbed and utilized by the microorganisms,and some are released into the atmosphere as gas.