Above- and belowground response of baldcypress and water tupelo seedlings to variable rates of nitrogen loading: Mesocosm and field studies

•Studied impacts of nitrogen (0–400 g N m−2 yr−1) on baldcypress & water tupelo.•Aboveground biomass production increased steadily to 400 g N m−2 yr−1.•Belowground biomass production increased to 100 g N m−2 y−1 then decreased.•Wood density was largely unaffected by nitrogen loading rate.•Diameter increase for seedlings averaged from 1.1 to 2.5 cm yr−1.