MORPHOLOGICAL RESPONSES OF SEEDLINGS OF 4 SPECIES OF SALICACEAE TO DROUGHT

The riparian distribution patterns of floodplain species are affected by fluctuations in water level. Rapidly declining water levels in rive r banks during the growing period of plants can result in limited avai lability of water, particularly on coarse substrates. Differences in d rought resistance among Salix alba, Salix triandra, Salix viminalis, a nd Populus nigra, four species dominating river banks along the River Rhine, could explain part of the riparian distribution patterns. Morta lity and growth responses of seedlings grown under well-watered and dr y conditions were studied in a greenhouse experiment. Drought-induced mortality was 0% in S. alba and P. nigra, 37.5% in S. triandra, and 62 .5% in S. viminalis, which correlated with differences in water-loss c haracteristics of the species studied: S. triandra and S. viminalis ha d much higher transpiration rates under well-watered conditions than S . alba and P. nigra. Decreased shoot to root ratios were observed in a il species after 3 weeks of drought. The increase after drought of the root length to leaf area ratio was greatest for P. nigra, indicating that this species has a relatively efficient water economy. Specific l eaf areas of droughted plants decreased in S. alba and P. nigra, refle cting smaller transpiration areas. Drought also affected root distribu tions, resulting for all four species in deeper rooting and increased root length in deeper soil layers. Salix viminalis and S. triandra sho wed the greatest increase in root length in deep soil layers. We concl uded that P. nigra is most resistant to drought followed by S. alba an d then S. triandra and S. viminalis, and that these differences are re flected in the distribution patterns of these species observed on the banks of the River Rhine.