Elevated CO 2 stimulates grassland soil respiration by increasing carbon inputs rather than by enhancing soil moisture

E. Carol Adair, Peter B. Reich, Jared J. Trost, Sarah E. Hobbie

Research output: Contribution to journalArticlepeer-review

63 Scopus citations


It is not clear whether the consistent positive effect of elevated CO 2 on soil respiration (soil carbon flux, SCF) results from increased plant and microbial activity due to (i) greater C availability through CO 2-induced increases in C inputs or (ii) enhanced soil moisture via CO 2-induced declines in stomatal conductance and plant water use. Global changes such as biodiversity loss or nitrogen (N) deposition may also affect these drivers, interacting with CO 2 to affect SCF. To determine the effects of these factors on SCF and elucidate the mechanism(s) behind the effect of elevated CO 2 on SCF, we measured SCF and soil moisture throughout a growing season in the Biodiversity, CO 2, and N (BioCON) experiment. Increasing diversity and N caused small declines in soil moisture. Diversity had inconsistent small effects on SCF through its effects on abiotic conditions, while N had a small positive effect that was unrelated to soil moisture. Elevated CO 2 had large consistent effects, increasing soil moisture by 26% and SCF by 45%. However, CO 2-induced changes in soil moisture were weak drivers of SCF: CO 2 effects on SCF and soil moisture were uncorrelated, CO 2 effect size did not change with soil moisture, within-day CO 2 effects via soil moisture were neutral or weakly negative, and the estimated effect of increased C availability was 14 times larger than that of increased soil moisture. Combined with previous BioCON results indicating elevated CO 2 increases C availability to plants and microbes, our results suggest that increased SCF is driven by CO 2-induced increases in substrate availability. Our results provide further support for increased rates of belowground C cycling at elevated CO 2 and evidence that, unlike the response of productivity to elevated CO 2 in BioCON, the response of SCF is not strongly N limited. Thus, N limited grasslands are unlikely to act as a N sink under elevated CO 2.

Original languageEnglish (US)
Pages (from-to)3546-3563
Number of pages18
JournalGlobal change biology
Issue number12
StatePublished - Dec 2011


  • BioCON
  • Cedar Creek LTER
  • Diversity
  • FACE
  • Nitrogen additions
  • Soil carbon flux


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