Feeding rates of the woodlouse Armadillidium vulgare on herb litters produced at two levels of atmospheric CO2

The consumption and assimilation rates of the woodlouse Armadillidium vulga re were measured on leaf litters from five herb species grown and naturally senesced at 350 and 700 mul l(-1) CO2. Each type of litter was tested sepa rately after 12, 30 and 45 days of decomposition at 18 degreesC. The effect s of elevated CO2 differed depending on the plant species. In Medicago mini ma (Fabaceae), the CO2 treatment had no significant effect on consumption a nd assimilation. In Tyrimnus leucographus (Asteraceae), the CO2 treatment h ad no significant effect on consumption, but the elevated CO2 litter was as similated at a lower rate than the ambient CO2 litter after 30 days of deco mposition. In the three other species, Galactites tomentosa (Asteraceae), T rifolium angustifolium (Fabaceae) and Lolium rigidum (Poaceae), the elevate d CO2 litter was consumed and/or assimilated at a higher rate than the ambi ent CO2 litter. Examination of the nitrogen contents in these three species of litter did not support the hypothesis of compensatory feeding, i.e. an increase in woodlouse consumption to compensate for low nitrogen content of the food. Rather, the results suggest that in herbs that were unpalatable at the start of the experiment (Galactites, Trifolium and Lolium), more of the the litter produced at 700 mul l(-1) CO2 was consumed than of that prod uced at 350 mul l(-1) because inhibitory factors were eliminated faster dur ing decomposition.