Characteristics And Mechanisms Of Phosphorus Biogeochemical Cycling Between Sediment And Water For Wetlands Subjected To Warming: Microcosmic Investigation

Global warming poses a broad impact to the ecosystem in surface earth, among which the biogeochemical cycling of phosphorus (P) in the water-sediment interface of wetland responding to the warming is particular to expatiate with the purpose of wetland ecological stability and water quality improvement. In this paper, we collected six types of wetlands with a significant difference in P and carbon pools laying in the south of the Yangtze River Delta. An outdoor computerized microcosm was setup since July 2008 to simulate the climate scenario of ambient temperature (CK) and ambient temperature +5℃(UP). The application of modern analytical techniques was conducted to study the characteristics of P biogeochemical cycling during the sediments, water and microorganisms in wetland subjected to warming.According to the microcosmic experiment, the data showed that climate warming had slight effect on the content of Ca-P, only a few forms of P were significantly different. The concentrations of total phorphorus (TP) and dissoluble reactive phosphorus (DRP) in the overlying water from JH (Jinghu wetland), XZ (Xiazhuhu wetland) and SJ (Shijiuyang wetland) were significantly higher under UP treatment than that under CK in winter. The concentrations of P in porewater were significantly impacted by climate warming, in particular, the sediments from the wetland XZ and XX (Xixi wetland). The warming would be more favorable to enhance the concentrations of TP and DRP in overlying water and porewater for the sediments rich of Fe-P and Al-P.The analysis of PLFA (phospholipid fatty acid) showed that 16:0 was the main PLFA in JH,XZ,XX,SJ, and 16:1 w7c/15 iso 2OH was the main types in YT (Yatang wetland) and BY (Baoyang wetland). The types of PLFA in the differrent sediments increased more than 0.1% because of climate warming, except for YT. The amounts of total PLFA, bacteria and fungi under UP treatment were significantly higher than under CK treatment, the increasing percentages of which were found as 11%～67%,6%～83%,40%～168%, respectively. There were no significant changes in actinomycetes. The results showed that climate warming would increase the abundance of fungi and reduce the abundance of bacteria.Through the principal component analysis, climate warming could change the homogeneity and reduce the variation of PLFA。The application of enzymatic methods in wetland sediments and the determination of active organic matter showed that the warming would be more favorable to enhance the activity of neutral phosphatase and alkaline phosphatase for the wetland sediment deficient of P while neutral phosphatase mainly for sediments rich of P. Lower phosphatase activity in P-rich sediment was mainly due to the combination of organic matter and phosphatase, or the inhibition of high P concentration. The contents of high and middle active organic matter under CK treatment were higher than that under UP treatment. However low-active organic matter has the opposite phenomenon. Microbes can use the high and middle organic matter easily. The total contents of active organic matter under UP treatment were higher than that under CK treatment, which showed that the wetland ecosystem was a carbon sink in the short-term.The impact of climate changes on wetland ecology is dynamic, complex and lasts for a long time. So it is necessery to clarify the characteristics and mechanisms of phosphorus biogeochemical cycling between sediment, water and microorganism on the basis of the short-term experiment.