Influence of water availability on competitive interactions between plant species on sandy soils

The gravimetric soil water content of four different successional stages of inland dune vegetation revealed pronounced seasonal changes and particular ly a major drought period in the late summer. In order to analyze the effec t of these seasonal water changes on the competitive interactions of two do minant species (Carex arenaria and Deschampsia flexuosa) in one of these st ages root development was compared under experimentally manipulated water c onditions in a minirhizotron experiment. Under well-watered conditions, the root growth of C. arenaria and D. flexuosa was not influenced by competiti on, but was significantly reduced for C. arenaria at low water availability . Accordingly, the relative yield based on total biomass was significantly lower under water shortage than under well-watered conditions for C. arenar ia, indicating higher interspecific competition compared to intraspecific c ompetitive interactions. These results indicate (i) that soil water status is an important factor for belowground competitive interactions and (ii) th at seasonal changes in soil water content may have a pronounced effect on t he outcome of competition and, in consequence, on the structure of the resp ective plant communities.