Variation in plant functional traits such as biomass production and litter chemistry among dominant plant species can have consequences for ecosystem processes. Here, we investigate how dominant plant species influence ecosystem carbon (C) and nitrogen (N) stocks, litter quantity and quality, soil C mineralization rates, and N transformation (mineralization and nitrification) rates in Michigan wetlands. We hypothesized that invasive species (such as Phalaris arundinacea and Phragmites australis) have greater nutrient use efficiency (NUE) compared to native species resulting in lower quality litter inputs and increased C and N storage in litter and surface soil layers. We also hypothesized that soil C and N mineralization rates will be influenced by the dominant vegetation due to the quantity and quality of litter inputs, and that these litter characteristics will differ among invasive species. First, we conducted a regional survey of marsh communities near the Kellogg Biological Station in central Michigan, and characterized community composition, key plant traits such as productivity and tissue chemistry, as well as litter and soil chemical and physical properties. Second, we performed a laboratory incubation to characterize soil C quality and mineralization rates at a subset of sites characterized by monocultures of invasive species. Finally, we conducted a second laboratory incubation to determine potential net N mineralization and nitrification rates.
Results/Conclusions
Our analyses show that the degree of P. arundinacea invasion is positively correlated with litter C and N stocks, and total invasive species biomass and litter chemistry are significant predictors of soil C and N stocks. Incubation results show significant main effects of dominant species and incubation temperature, with the highest soil C mineralization rates occurring in Typha-dominated sites and the lowest mineralization rates occurring at P. australis and P. arundinacea sites at room temperature (21 oC). Lastly, our laboratory incubations investigating species effects on soil net N transformation rates show significant differences in N mineralization and nitrification rates among monocultures of invasive species, with the highest N transformation rates at sites dominated by P. australis. Nitrogen transformation rates correlate positively with soil %C and %N, which is dependent on the identity of the dominant species. Our future work will utilize an experimental framework for investigating linkages and feedbacks between plant traits, species competition, microbial community composition and litter and soil processes.
