MORPHOLOGICAL TRAITS AND SPATIAL HETEROGENEITY OF AQUATIC PLANTS ALONG SEDIMENT AND DEPTH GRADIENTS, LAKE GENEVA, SWITZERLAND

The morphological response and distribution of Potamogeton pectinatus L., P. lucens L. and P. perfoliatus L. were investigated in relation t o sediment and depth gradients within the littoral zone of Lake Geneva . Biomass, maximum shoot length, shoot biomass and biomass density wer e the plant traits analyzed, together with sediment characteristics: t exture, water content, organic nitrogen and carbon, and exchangeable p hosphorus and potassium. The relationships between (i) depth and sedim ent characteristics vs. species distribution and (ii) depth and sedime nt characteristics vs. plant traits were first studied. Regression mod els for the biomass and the shoot length of each species are proposed. These models are applied in st related article (Lehmann et al., 1997) in order to study the relationship between plant traits vs. species d istribution through a Geographic Information System modeling. Besides the fact that P. pectinatus was more often found in sediments with hig her organic content, no direct relationships were found between sedime nt characteristics and species distribution, Neither could the presenc e of patches of bare substrate be explained by differences in sediment characteristics. The effect of the sediment characteristics on plant growth showed in general a negative influence of organic matter conten t (except for P. pectinatus), and a positive influence of the fine tex ture and phosphorus, P. pectinatus grew better in shallower water, P. lucens appeared to have the best competitive abilities and P. perfolia tus performed best at deeper sites.