The effect of seed addition and litter removal on plant composition in a coastal marsh of the Yellow River Delta

Abstract

A obvious feature of many coastal wetlands is the relatively low plant species richness across different plant zones. The mechanisms of low plant species richness in the coastal wetland still need to be investigated. On the other hand, seed addition and litter removal are traditional measures to increase plant species richness in degraded ecosystems (such as grasslands and forests), but the effects of these interventions has not been greatly explored in coastal wetlands. We performed a seed addition and litter removal experiment in three coastal marsh vegetative zones characterized by Suaeda salsa, Aeluropus pungens, and Phragmites australis in the Yellow River Delta. The results showed that seed addition and litter removal treatments did not increase the species richness, plant density, or above-ground biomass over one growth season in each zone. We further found that the mechanisms limiting these measures was salinity in S. salsa and A. pungens zones, and water inundation in the P. australis zone, which may limit seed germination and seedling recruitment. Specifically, seed addition increased plant density of P. australis in the early growth season (May and June), but decreased it dramatically at the end of the growth season (September) due to water inundation. The interactive effect of seed addition and litter removal on average plant height varied by plant zone and growth season. Limitations in both seed germination and seedling recruitment may lead to lower species richness in coastal marsh plant zones and, more generally, it is unlikely that seed addition and litter removal will increase species richness in plant zones of degraded coastal wetlands with high environmental stress.