Decomposition and nutrient dynamics of marsh litter in the Sanjiang Plain, Northeast China

The litterbag technique was used to study the decomposition and nutrient dynamics of marsh litter in the four communities, Carex pseudocuraica (C.pa), C. lasiocarpa (C.la), Deyeuxia angustifolia (D.aa), and D. angustifolia-Shrub (D.aa-Srb), in Sanjiang Plain, Northeast China. Decomposition was divided into two periods in the first year, with the mass loss ranging from 11.7% to 31.4% of the initial mass during summer and autumn, accounting for more than 75% of the annual loss. The decomposition rates ranged from 0.000 612 to 0.000 945 d−1 depending on the depth of the flooding and its duration, and differed significantly in each community. The litter decomposed faster in communities with deeper and perennial flooding than in those with shallow and seasonal flooding. The initial ratios of C:N and C:P were also different among the four litter types, but these differences had no impact on the decomposition rates, suggesting that the main factor influencing the decomposition rates of marsh litter was the flooding status rather than the litter quality. The N concentrations in C.pa and C.la almost continuously increased over time, with their final values being 2.8 and 2.4 times higher than the initial ones, respectively. However, the nutrient dynamics in D.aa and D.aa-Srb offered another pattern, sharply falling in the first month and then gradually rising, with the values at the end of the experiment being close to those at the beginning. The litter accumulated substantial amounts of N in C.pa and C.la, while net N release from the litter was observed in both D.aa and D.aa-Srb. The difference may be caused by microorganisms' demand for nutrition, and then limited by the C:N ratios of litter and the availability of nitrogen from the soil and marsh water. In contrast with N dynamics, P concentrations of all the litter types apparently decreased during the first month, and then continued to decline in C.pa, remained constant in C.la and D.aa and increased slightly in D.aa-Srb. At the end of the experiment, the P concentrations decreased, respectively, by 56%, −5%, 47% and 24% of the initial values of C.la, C. pa, D.aa and D.aa-Srb. The net P release was observed in all marsh litter over 480 days of decomposition and the intensity of the P release was different amongst communities, which may be regulated by ratios of initial C:P. The results suggested that in the marsh with the N limitation, litter tended to accumulate N and release P during decomposition and the intensity of accumulation or release was closely related to the initial C:N and C:P ratios.