ABOVEGROUND AND BELOWGROUND COMPETITION INTENSITY IN 2 CONTRASTING WETLAND PLANT-COMMUNITIES

A fundamental question in plant ecology is if and how the intensity of competition changes with productivity. This question has been the sou rce of considerable discussion during the last two decades, yet few ex periments have tested whether competition intensity changes with produ ctivity in nature. Even fewer studies have separated competition into its above- and belowground components in the field. We used a field ex periment to measure total competition intensity and its above- and bel owground components in two wetlands that represent extremes in habitat productivity: an infertile sandy shoreline and a fertile bay. Transpl ants of Lythrum salicaria and Carer crinita were grown with no neighbo rs, with roots of neighbors only, and with roots and shoots of neighbo rs; their growth rates were used to measure competition intensity (CI) . The experiment was carried out to answer the following main question s: (1) Is there a difference in total, above- and ground competition i ntensity in two wetlands that differ in standing crop? and (2) Is ther e an effect of standing crop on total, above- and belowground competit ion intensity when the data from the two wetlands are combined? Result s based on the average of both species show that total and aboveground competition intensity were greater in the high standing crop wetland, but belowground competition did not differ between wetlands (CITOTAL: P < 0.00001, CIABOVE: P = 0.0013, CIBELOW:P = 0.58). Total and aboveg round competition intensity were significantly affected by standing cr op in the wetlands studied but belowground competition intensity was n ot (Cl-TOTAL: P = 0.0001, CIABOVE: P = 0.0001, CIBELOW: P = 0.89). Res ults based on the two species separately show that species vary in the ir sensitivity to competition in wetland communities.