Light-acquisition traits link aboveground biomass and environment in inner saline-alkaline herbaceous marshes

A functional response-effect approach could predict how environmental changes affect ecosystem functioning. However, few studies have applied this approach to inner saline-alkaline marsh ecosystems where soil saline-alkaline, flooding/drought and nutrients stresses threat ecological functioning. To disentangle the relationships between environmental conditions and ecosystem functioning, a total of 81 plots were investigated across 22 marsh sites dominated by Phragmites australis and Bolboschoenus planiculmis in Western Songnen Plain wetlands, China. For both plant communities combined, deep flooding supported communities with higher specific leaf area (SLA), plant height and leaf nitrogen (N) content but lower leaf thickness. On the contrary, high soil salt content induced low leaf N and phosphorus (P) content, SLA and plant height. Only light acquisition-related trait, plant height and SLA, was the key traits which determined the relationships between ecosystem functioning (aboveground biomass) and saline-alkaline wetland environment. Yet indirect key traits related nutrient and water acquisition such as leaf thickness, N and P content were also found, and mediated the response of aboveground biomass through the allometric relationships with plant height or SLA. For the individual species community, only plant height was the key trait shared by P. australis and B. planiculmis, indicating the universality of plant height as a key trait for grass and sedge plants to explain how ecosystem functioning responds to abiotic factors. Hence, our findings suggest that saltmarsh plants are more inclined to alter light-acquisition traits to mediate the response of ecosystem functioning to environmental changes and that plant height is a particularly useful trait to predict plant productivity in earth system models under future environmental changes in inner saline-alkaline wetlands.