Decomposition of Eichhornia azurea from limnologically different environments of the Upper Paraná River floodplain

Abstract

Morphometrically distinct populations of Eichhornia azurea (Swartz) Kunth from environments with different limnological characteristics (Cortado Canal and Guarana Lake, both in the Upper Parana River floodplain), were incubated in the laboratory for 90 days. During this period, they were allowed to decompose in water of their original environment, or in water from reciprocally exchanged environments. The objectives were (a) to determine decomposition rates and changes in concentration of carbon, nitrogen and phosphorus in plant tissue and (b) to verify whether these rates and changes in tissue were affected by plant origin or by the characteristics of the water in which they were decomposing. Three distinct phases of decomposition were observed. In the first phase, ash content was rapidly lost. In the second, nitrogen increased and phosphorus decreased. In the third, both nitrogen and phosphorus increased. The results suggest that (a) changes in ash content and phosphorus concentration were similar in both environments; (b) the concentration of nitrogen remaining in the plant tissue was affected differently (ANOVA-Repeated, p<0.05) by the water from Cortado Canal and Guarana Lake; and (c) plants from different environments lost weight at different rates.