Nutrient release rates and ratios by two stream detritivores fed leaf litter grown under elevated atmospheric CO₂

Publisher： E. Schweizerbart'sche Verlagsbuchhandlung

ISSN： 0003-9136

Source： Archiv fuer Hydrobiologie, Vol.163, Iss.4, 2005-08, pp. : 463-477

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Abstract

We examined how nutrient release by two common stream detritivores, Asellus and Gammarus, was affected by the consumption of aspen leaf litter from trees grown under elevated CO₂. We measured excretory release of dissolved organic carbon (DOC), ammonia (NH₄), and soluble reactive phosphorus (SRP) from consumers fed senesced leaves of Populus tremuloides (trembling aspen) trees grown under elevated (720 ppm) and ambient (360 ppm) CO₂. Contrary to predictions based on ecological stoichiometry, elevated CO₂ leaves caused greater NH₄ and SRP release from both animals but did not affect the release of DOC. Elevated CO₂ leaves reduced DOC : NH₄ and DOC : SRP ratios released from Asellus but did not affect these ratios from Gammarus. Both animals showed lower NH₄ : SRP release ratios after eating elevated CO₂ leaves. A mass balance model of consumer N and P release demonstrated that increased excretion rates likely resulted from reduced absorption efficiencies (and unchanged or higher digestive efficiencies) in these aquatic detritivores. Our results indicate that changes in leaf biochemistry resulting from elevated atmospheric CO₂ will strongly affect the ability of stream consumers to retain important biogenic elements. Increased release rates of NH₄ and SRP are another indication, along with reduced growth and reproduction, that litter produced under elevated CO₂ has strong effects on key physiological processes in detritivores with potentially strong consequences for nutrient cycling in streams of forested regions.