B21F-0533
Climate change increases soil C losses from a corn-soy ecosystem

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Christopher K Black, University of Illinois at Urbana Champaign, Urbana, IL, United States, Sarah C Davis, Ohio University, Voinovich School for Leadership and Public Affairs, Athens, OH, United States, Tara W Hudiburg, University of Idaho, Forest, Rangeland, and Fire Sciences, Moscow, ID, United States, Carl Bernacchi, Global Change and Photosynthesis Research Unit, Agricultural Research Service, USDA, Urbana, IL, United States and Evan H DeLucia, University of Illinois at Urbana Champaign, Plant Biology, Urbana, IL, United States
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. Higher plant productivity from increased CO2 has been expected to raise soil carbon stocks by increasing root and litter inputs, but may instead prime microbial activity and cause further carbon losses. Previous work at SoyFACE has shown soil carbon to be declining, and this trend has continued despite more than ten years of higher carbon inputs from increased plant productivity under elevated CO2, supporting the hypothesis that new carbon is priming decomposition rather than organic matter accumulation. We elevated temperature (+3.5 °C) and CO2 (+200 ppm) for three years in a factorial experiment on a corn-soybean agroecosystem. We used mobile gas analyzers to monitor 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. We predicted that heat would accelerate the previously observed priming of organic matter decomposition, leading to higher respiration from heated elevated-CO2 plots and accelerated carbon losses over time.

Both heating and elevated CO2 increased respiration from soil microbes, but reduced repiration from roots and rhizosphere. The effects were additive, with no heat x CO2 interactions. Particulate organic matter and total soil C declined over time and were lower under elevated CO2 plots than in ambient plots, but did not differ between heat treatments. DayCent simulations of heated plots agreed with our observations and predicted loss of ~15% of SOC under heating, but simulations of elevated CO2 failed to capture the observed priming of SOC losses and instead predicted a ~4% gain in SOC. These results suggest that soil C models may need to explicitly consider priming effects and that Midwestern agricultural soils may lose C on a massive scale in the coming decades.

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