Effects of Light Intensity and Groundwater Level on the Growth of a Globally Rare Fen Plant

Fens are wetlands of conservation concern across temperate regions of the world. Understanding how abiotic factors affect typical fen plants will help to direct conservation efforts in these wetlands. Here, I examine how light and groundwater levels affect the growth of the globally rare fen plant Trollius laxus. Stem and biomass production were compared among plants grown at combinations of two groundwater levels (10 and 20 cm below the surface) and four light levels (6, 40, 77, and 90% photosynthetic photon flux density) in the greenhouse. Light intensity and groundwater level interactively affected T. laxus growth, with the highest plant performance at high light intensity and low groundwater level. Plants showed no response to differences in groundwater level when highly shaded, but as light intensity increased, stem and biomass production increased more quickly at the lower than at the higher groundwater level. Increased light caused greater biomass allocation to roots versus shoots, but groundwater level did not influence allocation patterns. That T. laxus is physiologically tolerant of higher light and lower groundwater levels suggests that it, like other typical fen plants, may be excluded from drier, more optimal wetlands or parts of wetlands by plants that are stronger competitors for light.