O desempenho de duas espécies de macrófitas emergentes congêneres (Polygonum) sob influência de nutriente e competição.

Abstract

Aquatic environments are known to present a spatio-temporal difference in nutrient concentration. Furthermore, other processes also interfere in the dynamics of aquatic macrophyte communities, such as interspecific competition. The performance of two species of emerging macrophytes, Polygonum ferrugineum and Polygonum acuminatum, was analyzed under the influence of the presence of competitor and nutrient variation. An experiment was carried out in which stem fragments of each species were planted in monoculture and mixed culture and submitted to two nutrient treatments: low and high. The experiment lasted 60 days. The measured parameters as well as the relative competition index (RCI) were analyzed using two-way ANOVA by permutation with two fixed factors (nutrient and species). The height and biomass parameters (aerial, root and total) were different among the species. In the biomass parameters there was a difference between the nutrients. The relative growth rate indicated a difference between the nutrient concentrations. Interaction between the factors was observed for height and root:shoot ratio. For the RCI, no significant difference was observed for any parameter. The development of individuals was not affected by the presence of a competitor. P. ferrugineum developed a greater amount of biomass than P. acuminatum. However, the growth rates between the species did not differ, indicating that there is no competitive advantage of the first species over the second species. Regarding nutrients, under conditions of high amount of nutrients, the parameters measured showed higher values, but the difference was not exacerbated. Under low nutrient conditions, the species P. ferruginum developed higher values, indicating phenotypic plasticity in the adjustment of the root portion, in order to find and absorb more nutrients. However, there is no competitive advantage, since the RCI does not express it. Therefore, the presence of competitors, the variation of nutrients and the interaction of these two factors do not explain the distribution of species in aquatic environments nor the dominance of P. ferrugineum over P. acuminatum in the distribution.