Variação na altura e na abundância de colmos e estruturas reprodutivas em populações pioneiras e maduras de Spartina alterniflora Loisel. e S. densiflora Brongn. ( Poaceae ) do sul do Brasil

This study aimed to quantify and elucidate the spatial variability of plant height and abundance of tillers and reproductive structures of the salt marsh grasses Spartina alterniflora Loisel. and Spartina densiflora Brongn. within and between pioneer ( 50 years of colonization) in southern Brazil. Both pioneer populations had taller tillers (p<0.01) than mature populations. Pioneer populations of S. densiflora also showed massive investment on tiller density (10,084 m-2), more infl orescences (557 m-2) and higher fecundity (16,258 seeds m-2) than the mature population (131 infl orescence m-2; 2,199 seeds m-2). High redox and reduction of phosphorus availability in the sediment away from the water line seem to explain decreasing densities of tiller and infl orescences inside S. densiflora mature populations. Fourteen percent of pioneer S. alterniflora tillers flowered and, on average, produced only 0.4 seeds per infl orescence and 76 seeds m-2, whereas mature population did not fl ower.