Experimental growth responses to groundwater level variation and competition in five British wetland plant species

New experimental evidence from controlled glasshouse studies was used to test previous empirical field observations about the interactions of hydrological dynamics with individual plant species in wetland habitats. Manipulation of water levels, and the presence/ absence of competitor species, produced significant morphological responses (e.g. resource allocation to above- and below-ground structures; plant height; leaf size; tiller production) in mature individuals of five freshwater wetland plant species characteristic of British northern poor-fen habitats. These responses provide evidence for potential advantages in survival and ability to spread vegetatively. The data also provide new insight into factors controlling the distribution of wetland plants along gradients of water table level, in the presence or absence of competing species. Although there were variations between species, the effects of competition were, in general, less than those attributable to hydrological regime.