Antecedent moisture and temperature conditions modulate the response of ecosystem respiration to elevated CO2 and warming

摘要

Terrestrial plant and soil respiration, or ecosystem respiration (R-eco), represents a major CO2 flux in the global carbon cycle. However, there is disagreement in how R-eco will respond to future global changes, such as elevated atmosphere CO2 and warming. To address this, we synthesized six years (2007-2012) of R-eco data from the Prairie Heating And CO2 Enrichment (PHACE) experiment. We applied a semi-mechanistic temperature-response model to simultaneously evaluate the response of R-eco 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 R-eco well (R-2=0.77). We applied the model to estimate annual (March-October) R-eco, 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 R-eco was stimulated by elevated CO2 singly (24%) or in combination with warming (28%). Warming had little effect on annual R-eco 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 R-eco can be partly attributed to the effects of antecedent SoilT and vegetation greenness on the apparent temperature sensitivity of R-eco and to the effects of antecedent and current SWC and vegetation activity (greenness modulated by VPD) on R-eco base rates. Thus, this study indicates that the incorporation of both antecedent environmental conditions and aboveground vegetation activity are critical to predicting R-eco at multiple timescales (subdaily to annual) and under a future climate of elevated CO2 and warming.