EFFECT OF SOIL-MOISTURE AND FERTILIZER APPLICATION ON CLONAL GROWTH AND REPRODUCTION IN A TRISTYLOUS WEED, LYTHRUM-SALICARIA

Clonal growth and reproduction in tristylous Lythrum salicaria L. were examined experimentally, using cloned genotypes of each of the three flower morphs, in field studies involving four moisture and three nutr ient treatments. Clonal growth was measured in terms of diameter of cl ones, number of ramets per clone, and total length of ramets, and an i ndex of reproduction was recorded as the total length of infructescenc e per clone. Neither clonal growth nor reproduction differed significa ntly among flower morphs, but both differed significantly as a consequ ence of both moisture and nutrient treatments. The pattern of seasonal growth indicates that ramet production was restricted mainly to the b eginning of the season following vigorous vegetative growth. Although flowering began in June, it was restricted to plants in drier treatmen ts in the water-gradient experiment. Characters intrinsic to tristyly (such as lengths of styles and stamens, and allocation of biomass to s tamens and pistil) differed significantly among morphs. Soil moisture levels but not fertilizer treatments significantly affected the size o f floral structures and biomass. Although absolute levels of biomass a llocation to whole flowers and to attractive structures did not differ significantly among morphs, relative allocation to stamens increased progressively from long morph to mid-morph to short morph, with a corr esponding decrease in relative mass of pistil. Although proportional a llocation differed significantly among morphs, it was unaffected by mo isture treatment, suggesting tight genetic control of herkogamy (spati al separation between anther and stigma). This should maintain the flo ral polymorphism in different ecological conditions.