PUB - Publikationen an der Universität Bielefeld

Monocultures and 1:1 mixtures of the highly competitive grass Elymus repens (L.) Gould and the low competitive grass Puccinellia distans (Jacq.) Parl. were grown under controlled conditions in a growth chamber at four different soil depths and under various water and nutrient conditions in order to evaluate whether shallow soil depth could be the determining factor in causing a stable coexistence of the two species, or dominance of P, distans, as recently observed in the shallow soil areas of Middle European road shoulders. As expected, above- and belowground biomass production of monocultures of both species was strongly reduced by shallow soils under all treatments. However, with decreasing soil depth, the aboveground biomass fraction of P. distans was found to markedly increase relative to that of E. repens in the mixtures, particularly if the plants were grown under water-stress conditions. Although biomass production of both species increased with high nutrient supply, nutrient levels did not affect the competitive relationship on shallow soils. Apparently, P. distans which naturally develops a rather extensive fine root system in the top 10-15 cm of soil is better able to effectively use the limited resources of shallow soil than the normally deeper rooted E. repens. In consequence, E. repens cannot produce enough aboveground biomass to effectively shade and ultimately exclude P. distans. Hydroculture experiments with both species at four different salinity levels revealed that biomass production of E. repens was more affected by salt stress than that of the facultative halophyte P. distans. Experiments are also presented which show that allelopathic effects of E. repens, which have been equivocally discussed in the literature, do not seem to affect biomass production of P. distans. It is concluded that shallow soil conditions are sufficient to create the observed patterns of co-occurrence at the roadside, but that common road treatments like winter salt application or frequent mowing of the road shoulders further enhance the competitive ability of P. distans in the shallow soil areas close to the pavement.