Breakdown and Colonization of Nothofagus Leaves in a New Zealand Stream

Abstract

Leaves of mountain beech, Nothofagus solandri var. cliffortioides (Hook f.) Poole immersed in a New Zealand stream in 1 mm mesh bags lost 49 % of their initial dry weight in 152 d. Ash-free weight declined from 95.5 % to 87.3 % of dry weight, percent carbon fluctuated within 4 % of its initial level and protein increased from I % to 6 % of leaf dry weight. An absolute increase in protein occurred in the first 3 wk. Aquatic hyphomycetes did not colonize leaves extensively. Diatoms were found in small numbers and bacteria were abundant on newly fallen and older leaves. Bags were colonized by 19 invertebrate species of which larval Chironomidae and nymphs of a stonefly Spaniocerca zelandica Tillyard were most abundant. A maximum density of 15 invertebrates per g dry weight of leaf was recorded after 152 days, however, total numbers per bag and species composition varied little with time. Insect feeding on bacterially conditioned leaves probably accounted for much of the leaf weight loss during the study.