Influence of environmental factors on the growth and interactions between salt marsh plants: effects of salinity, sediment and waterlogging

1 Artificial environmental gradients were established in a series of pot ex periments to investigate the effect of salinity, sediment type and waterlog ging on the growth, and interactions between Spartina anglica and Puccinell ia maritima. In each experiment, one environmental variable was manipulated and plants grown in pairwise combinations to examine the effect of the env ironmental factor on the intensity of intra- and interspecific interactions , quantified using the Relative Neighbour Effect (RNE) index. 2 Puccinellia was found to exert an asymmetric, one-way competitive dominan ce above ground over Spartina in experiments where gradients of sediment ty pe and waterlogging were established. The intensity of the competition was highest in conditions with the least abiotic stress and lower or non-existe nt where stress was increased. 3 The intensity of the above-ground competition was greatest in loam and le ast in sand sediments. Reduction in competitive intensity in sand was accom panied by an increase in below-ground Spartina biomass and it is suggested that the production of rhizomes is a potential mechanism by which this spec ies can expand vegetatively into areas without competition. 4 Interspecific competition on Spartina from Puccinellia also varied in int ensity in the waterlogging experiment, being more intense in non-immersed t reatments, where abiotic stress was reduced. 5 The competitive dominance of Puccinellia and the competition avoidance me chanism shown by Spartina in these experiments help to explain the successi onal interactions between the species along environmental gradients in natu ral salt marsh communities.