Data from: Top-down and bottom-up control of Spartina alterniflora characteristics beyond standing biomass

While the effects of top-down and bottom-up forces on aboveground plant growth have been extensively examined, less is known about the relative impacts of these factors on other aspects of plant life history, including belowground characteristics, litter production, and reproduction. In a season-long, fully factorial field experiment in a salt marsh in Virginia, USA, we manipulated grazing intensity (a top-down force) and nutrient availability (a bottom-up force) and measured the response in a suite of traits of smooth cordgrass (Spartina alterniflora), the dominant foundation species in the ecosystem. Three categories of traits and characteristics were measured: belowground characteristics, litter production, and reproduction, encompassing ten total responses. Of the ten response variables measured, nine were affected by treatments. Six response variables showed independent effects of grazing and fertilization, while three showed interactive effects. In general, fertilization led to increased cordgrass reproduction and belowground biomass, the latter of which conflicts with previous findings. Higher grazing intensity had negative impacts on both reproduction and belowground biomass. Our results indicate a complicated, yet predictable set of interactions between grazing and nutrient availability that influence relatively understudied traits of wetland plant structure. As many of these traits have been linked to key ecosystem functions, such as carbon burial, nutrient cycling, and ecosystem expansion, synthesizing the ecological knowledge and theory of top-down and bottom-up forces with trait-based methodologies may provide a promising path forward in predicting variability in ecosystem function.