Ecophysiological differences among Leymus mollis populations across a subarctic dune system caused by environmental, not genetic, factors

Plant species that persist during succession, from the colonization to the stabilization stages, face major environmental changes. Such changes are be lieved to have significant effects on species performance. In subarctic coa stal dune systems, Leymus mollis colonizes the embryo dunes, on the upper l imit of the beach. It reaches its maximum density on the foredune, but also grows on older, stabilized ridges. This paper reports on the phenotypic va riations of some ecophysiological traits associated with the persistence of L. mollis on a dune system on the east coast of Hudson Bay (northern Quebe c). Leymus mollis ramets tend to have a lower net carbon assimilation rate and water use efficiency, and a higher substomatal CO2 concentration on the stabilized dune than on the foredune. However, these physiological differe nces cannot be explained by differences in leaf morphology or nitrogen cont ent. Under controlled conditions, ecophysiological differences observed in the field disappear, suggesting that these are not genetic but determined b y environmental changes along the foredune-stabilized dune gradient. We pro pose that higher net carbon assimilation rate on the foredune might be rela ted to higher sink strength in relation to the growth-stimulating effect of sand burial.