Effect Of Salinity And Inundation On The Cyperus Malaccensis Litter Decomposition In The Minjiang Estuarine Tidal Wetlands

Coastal tidal wetland, located in the border of sea and land, is one of the most sensitive areas in the response to global climate change. Litter decomposition is a key process in biogeochemical cycle. Study on saltwater intrusion impact on litter decomposition in coastal tidal wetland has important significance for further understanding of coastal wetland biogeochemical cycle response to global climate change. Min River Estuary is one of most typical estuary wetlands in southeast coastal region in China, and Cyperus malaccensis is the main dominant species. Therefore, the observations in situ, microcosm and laboratory control experiments were performed to study the effects of salinity (0-15) and inundation (with and without inundation) on C. malaccensis litter decomposition and nutrient dynamic and its mechanisms. The main results showed as follows:(1) In situ experiments in Shanyutan (bracket water wetland) and Daoqingzhou (Freshwater wetland), the decomposition rate and litter total carbon (TC) and total nitrogen (TN) contents of C. malaccensis litter was no significant differences (p>0.05).(2) In microcosm and laboratory control experiments, the decomposition rate of C. malaccensis litter significantly suppressed with the rise of salinity from 0 to 15 (p<0.01). And the weightlessness rate of high salt treatment (salinity=15) in inundation and without inundation respectively decreased about 29.39% and 47.46% compared with the control treatment (salinity= 0). The contributions of the salinity factor to litter qulity, litter TC and TN were 27.30%,45.10% and 25.60%, respectively. The key factors of salinity effect on litter decomposition were litter ?-1, 4-N-acetylglucosaminidase (NAG) and acid phosphatase (AP), litter respiration rate, dissolved organic carbon (DOC) and chloride ion (C1-).(3) In microcosm and laboratory control experiments, the effect of inundation on decomposition rate of litter was related with decomposition phase. In the early decomposition phases, the inundation promoted the litter decomposition rate, while it inhibited the accumulation of litter C and N. The decomposition rate of litter witout inundation decreased about 11.07% to 18.74% compared with inundation treatment. However, in the middle and late decomposition phases, the inundation effect was on the contrary. The decomposition rate of litter witout inundation increased about 74.16% at most compared with inundation treatment. The contributions of the inundation factor to litter qulity, litter TC and TN were 15.72%,25.29% and 15.95%, respectively. The key factors of inundation effect on litter decomposition were litter ?-1,4-glucosidase (?G),?-1,4-N-acetylglucosaminidase (NAG) and acid phosphatase (AP), litter respiration rate and oxidation-deoxidation environment.(4) In microcosm and laboratory control experiments, the contributions of the salinity and inundation gradient interaction effect to litter qulity, litter TC and TN were 43.02%,70.38% and 41.56%, respectively. In the last phase of decomposition, the decomposition rate, litter TC and TN in high salt treatment with inundation respectively decreased 45.09%,17.37% and 11.51% compared with control treatment witout inundation. The key influence mechanism were litter ?G, NAG and AP activity, litter respiration rate and oxidation-deoxidation environment. Moreover, a well coupling among litter decomposition rate, TC and TN contents and litter respiration rate, can reflect the decomposition phases.