USDA Scientists Study Effects of Rising Carbon Dioxide on Rangelands
By Don Comis
Rising carbon dioxide (CO2) levels can reverse the drying effects
of predicted higher temperatures on semi-arid rangelands, according to a
study published today in the scientific journal Nature by a team of U.S.
Department of Agriculture (USDA) and university scientists.
Warmer temperatures increase water loss to the atmosphere, leading to drier
soils. In contrast, higher CO2 levels cause leaf stomatal pores to partly
close, lessening the amount of water vapor that escapes and the amount of
water plants draw from soil. This new study finds that CO2 does more to
counterbalance warming-induced water loss than previously expected. In fact,
simulations of levels of warming and CO2 predicted for later this century
demonstrated no net change in soil water, and actually increased levels of
plant growth for warm-season grasses.
"By combining higher temperatures with elevated CO2 levels in an experiment
on actual rangeland, these researchers are developing the scientific
knowledge base to help prepare managers of the world's rangelands for what
is likely to happen as climate changes in the future," said Edward B.
Knipling, administrator of the Agricultural Research Service (ARS), USDA's
principal intramural scientific research agency.
The results cover the first four years of the eight-year Prairie Heating and
CO2 Enrichment (PHACE) experiment on native northern mixed grass rangeland.
The study is being conducted by the ARS Rangeland Resources Research Unit
(RRRU) at the High Plains Grasslands Research Station near Cheyenne, Wyo.
ARS plant physiologist Jack Morgan leads the study, which uses both CO2
pipelines and thermal infrared heaters to simulate global warming conditions
predicted for the end of the century: 600 parts per million (ppm) of
CO2-compared to today's average 390 ppm-and day/night temperatures raised by
3 and 5 degrees Fahrenheit, respectively.
Based on these findings, warmer temperatures would likely play a role in
changing the relative success of various grass types. "Only the warm-season
grasses had their growth boosted higher by CO2 and warmer temperatures,"
Morgan said. "If this leads to a competitive advantage for warm-season
grasses, it may increase the challenges faced by ranchers who desire
cool-season grasses for early-season forage."
Elise Pendall and David Williams at the University of Wyoming at Laramie and
Matthew Wallenstein at Colorado State University at Fort Collins also are
participating in the study, which will be completed in 2013. Retired ARS
soil scientist Bruce Kimball, designer of the infrared heater system, is
helping conduct the study. Kimball serves as a research collaborator at the
ARS U.S. Arid-Land Agricultural Research Center in Maricopa, Ariz.
Grass-dominated, dry rangelands account for approximately a third of the
Earth's land surface, providing most of the forage eaten by livestock. This
research, the first of its kind on this scale for rangelands, supports the
USDA priority of helping farmers and ranchers throughout the United States
and the rest of the world best adapt production practices to variable
climate patterns.
Morgan said more research is needed to determine how the water-savings
effect applies over the long run and in other types of semi-arid rangelands
as well as to croplands in semi-arid areas. "It is important to understand
that CO2 only offset the direct effects of warming on soil water in this
experiment, and that it is unlikely to offset more severe drought due to
combined warming and reduced precipitation projected for many regions of the
world," he said.
In addition to ARS funding, the research is supported by grants from the
National Science Foundation, the U.S. Department of Energy, and USDA's
National Institute of Food and Agriculture
By Don Comis
Rising carbon dioxide (CO2) levels can reverse the drying effects
of predicted higher temperatures on semi-arid rangelands, according to a
study published today in the scientific journal Nature by a team of U.S.
Department of Agriculture (USDA) and university scientists.
Warmer temperatures increase water loss to the atmosphere, leading to drier
soils. In contrast, higher CO2 levels cause leaf stomatal pores to partly
close, lessening the amount of water vapor that escapes and the amount of
water plants draw from soil. This new study finds that CO2 does more to
counterbalance warming-induced water loss than previously expected. In fact,
simulations of levels of warming and CO2 predicted for later this century
demonstrated no net change in soil water, and actually increased levels of
plant growth for warm-season grasses.
"By combining higher temperatures with elevated CO2 levels in an experiment
on actual rangeland, these researchers are developing the scientific
knowledge base to help prepare managers of the world's rangelands for what
is likely to happen as climate changes in the future," said Edward B.
Knipling, administrator of the Agricultural Research Service (ARS), USDA's
principal intramural scientific research agency.
The results cover the first four years of the eight-year Prairie Heating and
CO2 Enrichment (PHACE) experiment on native northern mixed grass rangeland.
The study is being conducted by the ARS Rangeland Resources Research Unit
(RRRU) at the High Plains Grasslands Research Station near Cheyenne, Wyo.
ARS plant physiologist Jack Morgan leads the study, which uses both CO2
pipelines and thermal infrared heaters to simulate global warming conditions
predicted for the end of the century: 600 parts per million (ppm) of
CO2-compared to today's average 390 ppm-and day/night temperatures raised by
3 and 5 degrees Fahrenheit, respectively.
Based on these findings, warmer temperatures would likely play a role in
changing the relative success of various grass types. "Only the warm-season
grasses had their growth boosted higher by CO2 and warmer temperatures,"
Morgan said. "If this leads to a competitive advantage for warm-season
grasses, it may increase the challenges faced by ranchers who desire
cool-season grasses for early-season forage."
Elise Pendall and David Williams at the University of Wyoming at Laramie and
Matthew Wallenstein at Colorado State University at Fort Collins also are
participating in the study, which will be completed in 2013. Retired ARS
soil scientist Bruce Kimball, designer of the infrared heater system, is
helping conduct the study. Kimball serves as a research collaborator at the
ARS U.S. Arid-Land Agricultural Research Center in Maricopa, Ariz.
Grass-dominated, dry rangelands account for approximately a third of the
Earth's land surface, providing most of the forage eaten by livestock. This
research, the first of its kind on this scale for rangelands, supports the
USDA priority of helping farmers and ranchers throughout the United States
and the rest of the world best adapt production practices to variable
climate patterns.
Morgan said more research is needed to determine how the water-savings
effect applies over the long run and in other types of semi-arid rangelands
as well as to croplands in semi-arid areas. "It is important to understand
that CO2 only offset the direct effects of warming on soil water in this
experiment, and that it is unlikely to offset more severe drought due to
combined warming and reduced precipitation projected for many regions of the
world," he said.
In addition to ARS funding, the research is supported by grants from the
National Science Foundation, the U.S. Department of Energy, and USDA's
National Institute of Food and Agriculture
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