[Effects of simulated wetland water change on the decomposition and nitrogen dynamics of Calamagrostis angustifolia litter].

From May 2005 to September 2006, the potential effects of wetland water change on the decomposition and nitrogen (N) dynamics of the typical meadow Calamagrostis angustifolia (TMC) and marsh meadow C. angustifolia (MMC) litters were studied by litterbag technique in the typical depressional wetland in the Sanjiang Plain. In this study, the natural water gradient in the depressional wetland was applied to simulate the changes of wetland water conditions, and six decomposition sub-zones were laid in turn in the six communities, Carex pseudocuraica (PF), Carex lasiocarpa (MG), Carex meyeriana (WL), Marsh meadow C. angustifolia (XII), Typical meadow C. angustfolia (XI), and Island forest (DZL), along the water gradient. The results show that water condition has significant effects on the decomposition of litters. If the hydrous environment is formed in C. angustfolia wetland due to the change of precipitation pattern in the future, the litter weightless rates of TMC and MMC will increase 4.33%-16.76% and 24.84%-53.97%, the decomposition rates will increase 10.51%-32.73% and 77.85%-93.92%, and the 95% decomposition time will decrease 0.72-1.85 a and 3.67-4.05 a, respectively. The changes of N contents and N accumulation indices of TMC and MMC litters are relatively consistent, but the change patterns indifferent sub-zones are different. In general, the N in litters in DZL, XI, WL, MG and PF sub-zones show the alternant change characteristics of release and accumulation, but the release process is predominated. In contrast with that, the N in litters in XII sub-zone show release at all times. The C/N ratios have important regulation functions to the changes of N in litters in decomposition process. The estimation results show that the N standing crops of TMC and MMC litters are 12.75 g x m(-2) and 8.29 g x m(-2), and the N annual returning amounts are larger than 1.95 g x (m2 x a)(-1) and 2.25 g x (m2 x a)(-1), respectively. The studies of affecting factors indicate that temperature has promotion effects on the relative decomposition rates of litters, while water condition has restraint effects on them. Further analysis shows that the relative decomposition rates, to some extent, depend on the substrate quality of litters if the nutrient status of decomposition environment does not change greatly. In reverse, if the nutrient status of decomposition environment changes greatly, the relative decomposition rates, to some extent, depend on the supply status of nutrient in decomposition environment.