Location: Rangeland Resources & Systems ResearchTitle: Antecedent moisture and temperature conditions modulate the response of ecosystem respiration to elevated CO2 and warming
|Ryan, Edmund - Arizona State University|
|Ogle, Kiona - Arizona State University|
|Zelikova, Tamara - University Of Wyoming|
|Williams, David - University Of Wyoming|
|Morgan, Jack - Retired ARS Employee|
|Pendall, Elise - University Of Western Australia|
Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2015
Publication Date: 2/21/2015
Citation: Ryan, E.M., Ogle, K., Zelikova, T.J., Lecain, D.R., Williams, D.G., Morgan, J.A., Pendall, E. 2015. Antecedent moisture and temperature conditions modulate the response of ecosystem respiration to elevated CO2 and warming. Global Change Biology. 21:2533-2602.
Interpretive Summary: This study reports on the ecosystem respiration responses in a multi-factor global climate change experiment on the mixed-grass-prairie of Wyoming. The Prairie Heating and CO2 Enrichment (PHACE) experiment treated native prairie experimental plots to a factorial of elevated CO2 (nearly twice current levels) and warming levels that are predicted for the end of this century. Ecosystem respiration is a critical parameter as it reflects biological activity in the plants and soil (roots, microbes etc.) and is an important feedback on the problem of globally increasing CO2 concentrations. Six years of continual measurements show that elevated CO2 increases ecosystem respiration, which will contribute to global CO2 pollution. This also suggests that the prairie carbon cycle (C) will be stimulated by elevated CO2, a negative feedback on the problem. Warming had little effect on ecosystem respiration at current CO2 levels, but had an additive effect under elevated CO2. This suggests that future conditions of higher CO2 and warmer temperatures will have a large negative feedback on the grassland carbon cycle. The study also showed that conservation of soil water under elevated CO2 (due to reduced plant transpiration) plus increased plant growth under elevated CO2 were the main driving factors in higher ecosystem respiration. These findings contribute greatly to the knowledge of grassland responses to climate change and will greatly improve efforts to model ecosystem responses to global climate change.
Technical Abstract: Terrestrial plant and soil respiration, or ecosystem respiration (Reco), represents a major CO2 flux in the global carbon cycle. However, there is disagreement in how Reco will respond to future global changes, such as elevated atmosphere CO2 and warming. To address this, we synthesized six years (2007–2012) of Reco data from the Prairie Heating And CO2 Enrichment (PHACE) experiment. We applied a semi-mechanistic temperature–response model to simultaneously evaluate the response of Reco to three treatment factors (elevated CO2, warming, and soil water manipulation) and their interactions with antecedent soil conditions [e.g., past soil water content (SWC) and temperature (SoilT)] and aboveground factors (e.g., vapor pressure deficit, photosynthetically active radiation, vegetation greenness). The model fits the observed Reco well (R2 = 0.77). We applied the model to estimate annual (March–October) Reco, which was stimulated under elevated CO2 in most years, likely due to the indirect effect of elevated CO2 on SWC. When aggregated from 2007 to 2012, total six-year Reco was stimulated by elevated CO2 singly (24%) or in combination with warming (28%). Warming had little effect on annual Reco under ambient CO2, but stimulated it under elevated CO2 (32% across all years) when precipitation was high (e.g., 44% in 2009, a ‘wet’ year). Treatment-level differences in Reco can be partly attributed to the effects of antecedent SoilT and vegetation greenness on the apparent temperature sensitivity of Reco and to the effects of antecedent and current SWC and vegetation activity (greenness modulated by VPD) on Reco base rates. Thus, this study indicates that the incorporation of both antecedent environmental conditions and aboveground vegetation activity are critical to predicting Reco at multiple timescales (subdaily to annual) and under a future climate of elevated CO2 and warming.