Ecotypic differentiation in relation to soil nitrogen in northern Scandinavian Cochlearia officinalis

Ecotypic differentiation of Cochlearia officinalis L. was studied in four populations, roughly described as "beach", "bird cliff", "spring" and "estuary", which occupy different habitats in the northern part of Norway. The plants were cultivated under controlled conditions on soil to which nitrogen was applied at various amounts (0, 0.2 and 1.0 g N pot^?1). The above ground part of the "bird cliff" population showed the highest dry weight and nitrogen uptake at the highest nitrogen concentration. No effect of nitrogen treatment and the lowest dry weight were found in the "estuary" population. The differences in population response to added nitrogen were correlated to the nitrogen content of the soil in their natural habitat. Morphological features of the populations were also significantly different. The "estuary", "beach" and "bird cliff" populations showed differences in all characteristics measured – ratio of length/width of the leaves, shape of the leaf base, and length of the petiole. "Beach" and "spring" differed significantly in petiole length, while "bird cliff" and "spring" differed significantly in both leaf ratio and shape of the leaf base. These morphological features were not significantly altered by the application of nitrogen to the soil. This study shows that the four populations of Cochlearia officinalis are discrete biotypes characteristic of distinct habitats, and therefore, should be considered ecotypes.