Cellulase and xylanase activity during the decomposition of three aquatic macrophytes in a tropical oxbow lagoon

Due to the connection between enzymatic activity and degradation of different fractions of organic matter, enzyme assays can be used to estimate degradation rates of particulate and dissolved organic carbon in freshwater systems. The aim of this study was to quantify and model the enzymatic degradation involving the decomposition of macrophytes, describing temporal activity of cellulases (EC 3.2.1.4 and EC 3.2.1.91) and xylanase (EC 3.2.1.8) during in situ decomposition of three aquatic macrophytes (Salvinia sp., Eichhornia azurea and Cyperus giganteus) on the surface and water-sediment interface (w-s interface) of an oxbow lagoon (Óleo lagoon) within a natural Brazilian Savanna Reserve. Overall, the enzymatic degradation of aquatic macrophytes in Óleo lagoon occurred during the whole year and was initiated together with leaching. Xylanase production was ca. 5 times higher than cellulase values due to easy access to this compound by cellulolytic microorganisms. Enzymatic production and detritus mass decay were similar on the surface and w-s interface. Salvinia sp. was the most recalcitrant detritus, with low mass decay and enzymatic activity. E. azurea and C. giganteus decomposition rates and enzymatic production were high and similar. Due to the physicochemical homogeneity observed in the Óleo lagoon, the differences between the decay rates of each species are mostly related with detritus chemical quality.

Decomposição e dinâmica de liberação de nitrogênio e fósforo de frações vegetais de Salvinia auriculata Aubl em um reservatório da Amazônia legal / Decomposition and release dynamics of nitrogen and phosphorous from vegetal fractions of Salvinia auriculata Aubl in a Legal Amazon reservoir

Este estudo teve como objetivo determinar os coeficientes de decomposição da parte submersa (PS) e aérea (PA) de Salvinia auriculata em duas profundidades da coluna de água (superfície e sedimento). Também visou avaliar o rendimento do processo de perda de massa assim como a evolução temporal dos teores de fósforo e nitrogênio. As macrófitas foram separadas em partes; em seguida, foram secas até peso constante. Os materiais vegetais foram depositados em sacos de decomposição e incubados no reservatório da UHE Lajeado, Tocantins. As análises dos resultados de perda de massa revelaram que não houve diferenças significativas entre os PA-sed e PA-sup (p > 0,05), entretanto, os PA-sed foram significativamente diferentes dos PS-sed (p < 0,05) e dos PS-sup (p < 0,01). Os PA-sed apresentaram k = 0,0102 dia-1 e as incubadas na superfície (PA-sup) um k = 0,0067 dia-1, os PS-sed apresentaram um k = 0,0027 dia-1 e os PS-sup um k = 0,0040 dia-1. Durante os primeiros dias de decomposição foram liberadas grandes concentrações de fósforo e nitrogênio pelo processo de lixiviação; a partir do 14º dia foi observada uma tendência de aumento nas concentrações de nitrogênio, fato provavelmente relacionado com o enriquecimento dos detritos pela biomassa microbiana.

This study aimed to determine the decomposition coefficients of the submerged (SP) and aerial part (AP) of S. auriculata at two different depths within water column (surface and sediment). It also quantified the decomposition yield of S. auriculata and the temporal changes of nitrogen and phosphorous content of the remaining biomass. The macrophytes were fractionated in parts and were dried in sequence until attaining constant weight. The litterbags with plant material were incubated in the reservoir of UHE Lajeado. The results of mass loss showed that there were no significant differences among the AP-sed and AP-sur (p > 0.05). However, the AP-sed was significantly different from SP-sed (p < 0.05) and SP-sur (p < 0.01). The AP-sed presented a decay coefficient (k) of 0.0102 day-1 and AP-sur a k of 0.0067 day-1. The SP-sed presented a k of 0.0027 day-1 and the SP-sur 0.0040 day-1. It was also noticed that during the first days of decomposition great amounts of nitrogen and phosphorous were solubilized. This event was related to the leachate process; from the 14th day of decomposition, an increasing trend was observed in nitrogen concentrations. This fact was probably related to detritus enrichment by microbial colonization.