Effects of Elevated CO(2) on Litter Chemistry and Subsequent Invertebrate Detritivore Feeding Responses

Elevated atmospheric CO(2) can change foliar tissue chemistry. This alters leaf litter palatability to macroinvertebrate detritivores with consequences for decomposition, nutrient turnover, and food-web structure. Currently there is no consensus on the link between CO(2) enrichment, litter chemistry, and macroinvertebrate-mediated leaf decomposition. To identify any unifying mechanisms, we presented eight invertebrate species from aquatic and terrestrial ecosystems with litter from Alnus glutinosa (common alder) or Betula pendula (silver birch) trees propagated under ambient (380 ppm) or elevated (ambient +200 ppm) CO(2) concentrations. Alder litter was largely unaffected by CO(2) enrichment, but birch litter from leaves grown under elevated CO(2) had reduced nitrogen concentrations and greater C/N ratios. Invertebrates were provided individually with either (i) two litter discs, one of each CO(2) treatment (‘choice’), or (ii) one litter disc of each CO(2) treatment alone (‘no-choice’). Consumption was recorded. Only Odontocerum albicorne showed a feeding preference in the choice test, consuming more ambient- than elevated-CO(2) birch litter. Species’ responses to alder were highly idiosyncratic in the no-choice test: Gammarus pulex and O. albicorne consumed more elevated-CO(2) than ambient-CO(2) litter, indicating compensatory feeding, while Oniscus asellus consumed more of the ambient-CO(2) litter. No species responded to CO(2) treatment when fed birch litter. Overall, these results show how elevated atmospheric CO(2) can alter litter chemistry, affecting invertebrate feeding behaviour in species-specific ways. The data highlight the need for greater species-level information when predicting changes to detrital processing–a key ecosystem function–under atmospheric change.