Habitat-specific genetic effects on growth rate and morphology across pH and water-level gradients within a population of the moss Sphagnum angustifolium (Sphagnaceae)

To study genetic adaptations in bryophytes on small ecological and spatial scales and to assess the adaptive significance of morphological trait varia tion, genotypes of Sphagnum angustifolium originating from habitats charact erized by different pH and height above water table were clonally propagate d and grown along the same gradients that exist in the field. Clones from o mbrotrophic habitats grew consistently better ombrotrophically than clones from minerotrophic habitats and vice versa, suggesting that the genotypes w ere adapted to different pH levels. Genetic variation was found in several morphological traits, but habitat-specific genetic effects were detected on ly in length of spreading branches. Covariation between morphology and grow th was generally environmentally induced. Positive and negative cross-envir onment genetic correlations suggested the presence of constraints on adapti ve reaction norm evolution. The indications of small-scale genetic adaptati ons suggest either selective establishment of genotypes adapted to specific habitats, strong selective forces operating at the later stages of the lif e cycle, restricted gene how over short distances, or a combination of thes e. In contrast to prevailing views, these results indicate that bryophytes are likely to respond genetically to small-scale environmental gradients.