Global Warming’s Ecosystem Double Whammy
Plants and soils act like sponges for atmospheric carbon dioxide, but new research finds that one abnormally warm year can suppress the amount of carbon dioxide taken up by some grassland ecosystems for as long as two years. The findings followed an unprecedented four-year study of sealed, 12-ton containerized grassland plots at the Desert Research Institute (DRI) in Reno, Nev.
“We confirmed that ecosystems respond to climate change in a much more complex way than one might expect based solely on traditional experiments and observations,” said study co-author James Coleman, Rice vice provost for research and professor of ecology and evolutionary biology. “Our results provide new information for those who are formulating science-based carbon policies.”
The four-year study involved native Oklahoma tallgrass prairie ecosystems that were sealed inside four living-room-sized environment chambers. To minimize the disturbance of plants and soil bacteria, a dozen of the 12-ton, six-foot-deep plots were extracted intact from the University of Oklahoma’s prairie research facility near Norman, Okla., and moved to DRI, where scientists replicated the daily and seasonal changes in temperature and rainfall that occur in the wild.
Scientists found that ecosystems exposed to an anomalously warm year had a net reduction in CO2 uptake for at least two years.
Plants and soils in ecosystems help modulate the amount of CO2 in the atmosphere when plants, which need CO2 to survive, absorb the gas during spring and summer growing seasons, storing the carbon in their leaves, stems and roots. The stored carbon returns to the soil when plants die, and it is released back into the atmosphere by soil bacteria that feed on the dead plants.
This relatively stable cycle was disrupted in the second year of the study when half of the plots were subjected to temperatures typical of a normal year, and the other half were subjected to abnormally warm temperatures — on the order of those predicted to occur later this century by the Intergovernmental Panel on Climate Change. In the third year of the study, temperatures around the warmed plots were turned down again to match temperatures in the control plots. The CO2 flux — the amount of carbon dioxide moving between the atmosphere and biosphere — was tracked in each chamber for all four years of the study.
The scientists found that ecosystems exposed to an anomalously warm year had a net reduction in CO2 uptake for at least two years. These ecosystems trapped and held about one-third the amount of carbon in those years than did the plots exposed to normal temperatures.
“Large reductions in net CO2 uptake in the warm year were caused mainly by decreased plant productivity resulting from drought,” explained co-author Paul Verburg of DRI, “while the lack of complete recovery the following year was caused by a lagged stimulation of CO2 release by soil microorganisms in response to soil moisture conditions.”
The collaborative study, which also involved scientists from the University of Nevada, Reno; the University of Oklahoma; the University of New Hampshire; and the National Center for Atmospheric Research in Boulder, Colo., was funded by the National Science Foundation and was published in the journal Nature.Learn more:
tinyurl.com/5gwkz8