The role of invertebrates and aquatic fungi on the decomposition of eucalyptus leaves in streams

Resumo da comunicação apresentada no XII Congresso da Association Española de Limnología - IV Congresso Ibérico de Limnologia. CIMAR, Universidade do Porto, 5-9 Julho 2004.Leaves entering in streams are subject to physical abrasion, invertebrate fragmentation and microbial degradation. Fungi, particularly aquatic hyphomycetes, dominate microbial leaf decomposition and condition the leaves, increasing their palatability for invertebrate shredders. The aim of this work was to study the relative role of invertebrates and aquatic fungi on leaf decomposition of Eucalyptus globulus Labill. in two rivers of Northwest Portugal with different water chemistry. For that purpose, leaf decomposition was followed in coarse-mesh and fine-mesh bags. Physical, chemical and microbial analyses of the stream water, as well as, biotic indices and diversity measures applied to the invertebrates associated with leaves showed that the Guisande River had better water quality than the Este River. Decomposition rates of eucalyptus leaves were significantly higher in the Guisande River (k = 0.019 to 0.029 dˉ¹) than in the Este River (k = 0.009 to 0.011 dˉ¹). Significantly higher fungal biomass (up to 790 μg ergosterol gˉ¹ AFDM) and sporulation rates (up to 370 conidia mgˉ¹ AFDM dˉ¹) occurred in the Guisande River in comparison with the Este River (fungal biomass up to 280 μg ergosterol gˉ¹ AFDM; sporulation rates up to 90 conidia mgˉ¹ AFDM dˉ¹). Correspondence analyses applied to aquatic hyphomycete and invertebrate assemblages discriminated the two rivers and higher richness in taxa was found in the Guisande River. In this river, leaf decomposition rate was significantly higher in coarse-mesh than in fine-mesh bags. However, in the Este River no significant differences were found between coarse-mesh and fine-mesh bags, which can be attributed to the absence of shredders and low current velocity in this river