MICROBIAL ACTIVITY AND INVERTEBRATE COLONIZATION OF WOOD IN A NEW-ZEALAND FOREST STREAM

Breakdown and colonisation of buried and surface-incubated wood was ex amined in a beech forest stream in South Island, New Zealand. Comparis ons were also made of microbial activity on wood, leaves, and stones. Weight loss of sticks was initially slow, but after 11.5 months 39% of their initial dry weight had been lost. Microbial colonists were main ly fungal hyphae, fine actinomycete-like filaments and unicellular bac teria. Chironomid larvae, oligochaetes, and harpacticoid copepods were the most abundant animal colonisers. Incorporation of C-14-glucose by wood-surface biofilms increased in the first 3 months and was greater on surface-incubated than buried sticks. Endocellulase activity varie d over time, and very high values after 2 months were associated with dense patches of filamentous microorganisms. Similar microbial assembl ages developed on surface-incubated sticks, leaves and twigs, but fung i were not found on stones where diatoms predominated and endocellulas e activity was negligible. Results of preliminary experiments with dif fusion substrata suggested that the heterotrophic biofilm microflora w as nutrient-limited. Our findings indicate that wood surfaces can be i mportant sites of organic matter uptake and transfer in forest streams .