Effects of inundation and stranding on leaf litter decomposition and chemical transformation

Abstract

Inundation and stranding are important processes of the riparian ecosystem due to water level fluctuation. Plant litter decomposition is a key process that determines the accumulation of soil organic matter in riparian ecosystems, but little is known about the alternating effects of inundation and stranding on this process. Using litters of the grass species Heteropogon contortus, we studied how the remaining mass and nitrogen (N), δ13C and δ15N, and 13C-CPMAS NMR spectra responded to permanent inundation, temporary inundation and drying over a period of twelve months. Inundation (permanent or temporary) and stranding altered litter C and N dynamics. The δ13C declined in the immersed litters and was stable after the litters were transported to the grassland plots, while δ15N in the litters that were decomposing continually in the water rapidly increased during the earlier stage of decomposition. We observed a significant increase in the proportion of ketone, carboxyl, and alkyl in the permanently inundated litter samples compared with those of litters decomposed at terrestrial habitats at the final harvest. These results indicated that the effects of inundation on the decay of labile and recalcitrant litter components were asynchronous. The decomposing litters in the inundation treatment differed chemically from those in the terrestrial habitat treatments and were characterized by greater relative abundances of ketone C and carboxyl C. The higher values of alkyl/O-alkyl for the stranding litters that had higher mass remaining and C/N as compared to those of inundated litters that had lower mass remaining and C/N in the final harvest, suggested a relatively higher contribution of the recalcitrant components to the litter residues. Likewise, the effects of transient inundation depend on the timing of immersion and stranding.