Restored wetlands: interplay between environmental variables, aboveground and belowground plant traits, and carbon cycling.

Wetlands are crucial for biodiversity and climate change mitigation. Vast wetland areas have been lost through land-use intensification. Thus, restoration efforts have gained attention globally. We assessed relationships between environmental conditions, aboveground and belowground plant traits and carbon cycling in restored wetlands in Denmark, both grazed and ungrazed, compared to a baseline in near-natural wetlands. Wetland plant species strategy varied from acquisitive to conservative. More conservative species tended to have larger root diameters and higher percentages of root aerenchyma. However, at the community level, we found no evidence for differences in the suite of traits expressed in restored and near-natural wetlands. Environmental and carbon cycling variables were not consistently different between restoration treatments. Average summer carbon fluxes were highly variable, but net ecosystem exchange was negative, indicating sequestration of CO2. Groundwater level was the main driver of CO2 exchange in summer, with relatively dry sites tending to fix more carbon. Relationships between plant traits and carbon cycling were weak. Our results suggest that, for carbon cycling, plant community trait composition is less important than the abiotic environment, in particular, the water table depth. This shows that ecosystem functions can be restored, even in cases where plant biodiversity has not recovered.