Effect of soil moisture on the multi-component decomposition of wetland macrophytes

The effect of soil moisture on plant litter decomposition is one of the major focuses of decomposition research. In this study, 150-day laboratory experiments were conducted with the simulated soil environment under different moisture levels. Three macrophytes, Phragmites australis, Miscanthus lutarioriparius, and Carex cinerascens, were selected. The dry biomass weight, and nutrient concentrations of plant samples were measured during the experiment, and a modified bi-exponential formula was used to investigate the effects of soil moisture on plant decomposition under non-submerged conditions. The litter decomposition process is considered as the simultaneous exponential decomposition of labile and refractory components. The relationship between the decomposition rates of the two components and soil moisture was found to be exponential. The results showed that the modified formula with moisture factor agreed well with the dry weight data (R2 > 0.97). The mass fractions of the labile component were 5.9%, 11.3%, and 6.7% for P. australis, M. lutarioriparius, and C. cinerascens, respectively. As moisture increased from 50 to 90%, the decomposition rate k1 of labile part increased from 0.05 to 0.12 day−1, and k2 of refractory part increased from about 0.0007 to 0.006 day−1. Higher quality plant (with high N content and low C content) decomposed faster. The effect of different moisture levels on the microbial community in the experiment was not significant. Furthermore, a longer humidification time in one cycle can promote the decomposition of both parts. The proposed bi-exponential formula of plant decomposition can be used to estimate vegetation decomposition in alternating wetting and drying surface waters.