ABSTRACT
Oniscus asellus was fed alternatively with birch-or oak litter. The feeding performance showed that relative growth rates (= RGR) and efficiencies in converting ingested food (= ECI) and digested food (= ECD) into body mass as well were more affected by the food items than by the microflora. In contrast, the increase of approximate digestibility (= AD) by microorganisms, probably via their cellulase activity, was striking. Microflora, at an elevated density, increased AD-values from 45% to about 75% on birch, and oak litter as well. Additionally the microflora stimulated the increase of the consumption rates (RCR). On oak litter a 6-fold increase of RCR was observed. Increased food consumption is interpreted as a response to suboptimal nutrient levels in leaf litter to prevent large reductions in growth. When feeding O. asellus on birch litter there is enhanced cellulase activity but not dehydrogenase activity. On oak, litter enzyme activity was not affected by this isopod. These data indicate that Oniscus asellus benefits by stimulating the microbial activity. Also, grazers such as the Collembola Folsomia Candida improve the nutritional values of the litter consumed by Oniscus asellus. This was demonstrated for birch litter where F. Candida enhanced both dehydrogenase and cellulase activity. The analyses highlight the importance of interactions among microorganisms, microarthropods, and litter quality.
