VARIATION IN RELATIVE GROWTH-RATE AND ITS COMPONENTS IN THE ANNUAL POLYGONUM AVICULARE IN RELATION TO HABITAT DISTURBANCE AND SEED SIZE

Polygonum aviculare is an annual weedy species showing extensive genet ic variation in seed and leaf size and colonizing various types of man -disturbed habitats. A growth analysis was conducted on 12 genotypes r epresentative of three regimes of disturbance of natural habitat (tram pling, weeding, and no disturbance in the course of the growing season ), grown under productive conditions in order to test whether relative growth rate (RGR) varies at the intraspecific level and , if so, whic h growth parameters may explain its variation. RGR showed significant genotypic variation (0.355-0.452 g g(-1) day(-1)), positively correlat ed with specific leaf area (SLA) and leaf mass ratio (LMR) and negativ ely correlated with unit leaf rate per unit leaf area (ULR(A)). Thus, the paramount importance of leaf area ratio (LAR = SLAxLMR) in determi ning growth rate variation between different herbaceous species is con firmed at the intraspecific level in this species. Genotypes originati ng from trampled habitats had smaller seeds and smaller leaves than ge notypes from habitats subject to other disturbance regimes. Additional ly, they showed a lower LAR, not entirely compensated for by a higher ULR(A), which resulted in a positive allometric relationship between s eed size and RGR. It is hypothesized that their lower SLA, correlated with a higher leaf dry matter content (possibly a consequence of a hig her cell wall content per unit leaf area) and their lower LMR have bee n co-selected with small leaf size as adaptations promoting resistance to trampling stress. it is suggested that variation in cell size and/ or gibberellin content might be the mediators of the correlation found between seed size, leaf size and growth parameters within this specie s.