|BLACK, CHRISTOPHER - University Of Illinois|
|DAVIS, SARAH - Ohio University|
|HUDIBURG, TARA - University Of Idaho|
|DELUCIA, EVAN - University Of Illinois|
Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2016
Publication Date: 7/1/2016
Citation: Black, C.K., Davis, S.C., Hudiburg, T.W., Bernacchi, C.J., DeLucia, E.H. 2016. Elevated CO2 and temperature increase soil C losses from a soy-maize ecosystem. Global Change Biology. doi:10.111/gcb.13378.
Interpretive Summary: Soils respire carbon dioxide through microbial activity that breaks down organic matter. As soils get warmer, they respire more. However, there is very little predictive ability for rates of soil respiration as ecosystems warm. This experiment artificially warmed soils over three years using infrared heating technology. Respiration rates were measured routinely and used to develop an ecosystem model to simulate the effects of warming and rising atmospheric CO2 on soil respiration rates. The results show that the microbes released 10% more CO2 from increased activity in the warmer temperatures and higher CO2. The respiration from plant roots decreased by 25% in the heated plots. Because the microbes are consuming stored carbon, the increase in soil respiration in the heating will likely lead to losses of soil carbon and the rising in CO2 will not likely offset this effect.
Technical Abstract: Warming temperatures and increasing CO2 are likely to have large effects on the amount of carbon stored in soil, but predictions of these effects are poorly constrained. We elevated temperature (canopy: +2.8 °C; soil growing season: +1.8 °C; soil fallow: +2.3 °C) for three years within the 9th-11th years of an elevated CO2 (+200 ppm) experiment on a maize-soybean agroecosystem, measured respiration by roots and soil microbes, then used a process-based ecosystem model (DayCent) to simulate the decadal effects of warming and CO2 enrichment on soil C. Both heating and elevated CO2 increased respiration from soil microbes by ~10%, but heating reduced respiration from roots and rhizosphere by ~25%. The effects were additive, with no heat x CO2 interactions. Particulate organic matter and total soil C declined over time in all treatments and were lower in elevated CO2 plots than in ambient plots, but did not differ between heat treatments. We speculate that these declines indicate a priming effect, with increased C inputs under elevated CO2 fueling a loss of old soil carbon. Model simulations of heated plots agreed with our observations and predicted loss of ~15% of soil organic C after 100 years of heating, but simulations of elevated CO2 failed to predict the observed C losses and instead predicted a ~4% gain in soil organic C under any heating conditions. Despite model uncertainty, our empirical results suggest that combined, elevated CO2 and temperature will lead to long term declines in the amount of carbon stored in agricultural soils.