Original paper

Decomposition of eucalypt and alder mixtures: responses to variation in evenness

Gonçalves, Ana Lúcia Canhoto

Abstract

The relationship between diversity and function has only recently been investigated in stream ecosystems. Here we evaluated the effect of litter evenness on litter decomposition in single species and 2-species litter bags with Alnus glutinosa (L.) Gaertn. (A) and Eucalyptus globulus Labill. (E). The five evenness treatments (100 %A, 25 %E + 75 %A, 50 %A + 50 %E, 75 %E + 25 %A and 100 %E) simulated the relative proportions of both leaf species throughout the year in a eucalypt stream lined by alder trees. Decomposition rates of eucalypt were retarded in the presence of alder, while those of alder were stimulated in the presence of eucalypt. Differences in mass loss between treatments were unrelated to the initial quality of the mixtures. Globally, the effects of litter evenness on microbial parameters (O2 consumption, fungal biomass and sporulation) and invertebrate numbers ranged from undetectable to weak. This was probably due to high nutrient concentrations in the stream water that may have masked the potential stimulating effects promoted by the high quality of alder leaves on eucalypt biotic degradation. Although the effects of litter evenness on biotic parameters were idiosyncratic, the importance of species evenness on litter mass loss was suggested by the higher decomposition rates of the 50 %:50 % mixture, which is likely related to a trade-off between alder high nutrient quality and the stability promoted by eucalypt in the mixture. Alterations in litter evenness, resulting from changes in riparian composition and diversity, might affect litter decomposition, and consequently ecosystem function. These findings could be relevant for recovery and management of riparian zones.

Keywords

biodiversityevennessmicrobial activityfungiinvertebrates