Abstract
Elevated atmospheric CO2 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 CO2 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) CO2 concentrations. Alder litter was largely unaffected by CO2 enrichment, but birch litter from leaves grown under elevated CO2 had reduced nitrogen concentrations and greater C/N ratios. Invertebrates were provided individually with either (i) two litter discs, one of each CO2 treatment (‘choice’), or (ii) one litter disc of each CO2 treatment alone (‘no-choice’). Consumption was recorded. Only Odontocerum albicorne showed a feeding preference in the choice test, consuming more ambient- than elevated-CO2 birch litter. Species’ responses to alder were highly idiosyncratic in the no-choice test: Gammarus pulex and O. albicorne consumed more elevated-CO2 than ambient-CO2 litter, indicating compensatory feeding, while Oniscus asellus consumed more of the ambient-CO2 litter. No species responded to CO2 treatment when fed birch litter. Overall, these results show how elevated atmospheric CO2 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.
Highlights
Global concentrations of atmospheric carbon dioxide (CO2) could more than double by 2100 [1]
The effect of elevated CO2 on the chemical composition of green foliar tissues reduces its palatability to detritivores when it falls as litter [6]
Litter Chemistry CO2 enrichment altered leaf litter chemistry, but effects differed between tree species
Summary
Global concentrations of atmospheric carbon dioxide (CO2) could more than double by 2100 [1]. CO2 enrichment leads to increased plant photosynthesis, resulting in greater biomass and production [2]. Plant tissue chemistry is typically modified, with decreasing nitrogen concentrations and increasing carbon-nitrogen (C/N) ratios affecting herbivore life-history and feeding responses [3]. The effect of elevated CO2 on the chemical composition of green foliar tissues reduces its palatability to detritivores when it falls as litter [6]. Elevated CO2 can reduce litter resource quality by decreasing litter nitrogen content [7,8], subsequently increasing C/N ratios [9,10]. The potential for rising CO2 concentrations to alter litter chemical composition is established, but the consequences for invertebrate-mediated decomposition – an important ecosystem function – remain unclear [14]
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