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

Morphometrically distinct populations of Eichhornia azurea (Swartz) Kunth f rom environments with different limnological characteristics (Cortado Canal and Guarana Lake, both in the Upper Parana River floodplain), were incubat ed in the laboratory for 90 days. During this period, they were allowed to decompose in water of their original environment, or in water from reciproc ally exchanged environments. The objectives were (a) to determine decomposi tion 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 wh ich they were decomposing. Three distinct phases of decomposition were obse rved. In the first phase, ash content was rapidly lost. In the second, nitr ogen increased and phosphorus decreased. In the third, both nitrogen and ph osphorus increased. The results suggest that (a) changes in ash content and phosphorus concentration were similar in both environments; (b) the concen tration 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 .