Microbial biomass and activity in pine litter in the presence of Tomocerus minor (Insecta, Collembola)

Laboratory microcosms were used to study microbial populations and biomasses developing in fragmented litter of Pinus nigra Arnold var. nigra (A. et G.). Direct observations (fungal standing crop and fluorescein-stainable mycelia), litter enzyme analyses (cellulase and dehydrogenase), and measurements by physiological methods (microbial CO₂ production and total microbial, fungal, and bacterial viable biomasses) were made at 3-week intervals for 15 weeks. Most variables showed great changes during this period, which were ascribed to a rise in litter moisture content during the initial phase of the experiment, and to substrate depletion towards its final phase. The addition of the collembolan Tomocerus minor (Lubbock) for 1 week enhanced cellulase activities by 4%. When the animals were introduced after 6 weeks, the fungal standing crop was enhanced, and the percentage of fluorescein-stainable mycelia was reduced. Dehydrogenase activity was increased by grazing when the microbial population had been established for 9 weeks or longer. Eucaryotic and procaryotic substrate-induced respiration were positively correlated, which was explained by partial segregation of resources for the two groups. Litter cellulase and dehydrogenase activity showed correlations by other techniques, indicating their suitability as parameters for microbial activity in general, and for the collembolan grazing impact on microbial activity in particular.