Effects of Elevated CO2 on Methane Emissions from Terrestrial Plants Growing Under Aerobic Conditions
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In an effort to do so, Qaderi and Reid "examined the combined effects of temperature, carbon dioxide and watering regime on CH4 emissions from six commonly cultivated crop species: faba bean, sunflower, pea, canola, barley and wheat" in an experiment where "plants were grown from seeds in controlled-environment growth chambers under two temperature regimes (24°C day/20°C night and 30°C day/26°C night), two CO2 concentrations (380 and 760 ppm) and two watering regimes (well watered and water stressed)," where the "plants were first grown under 24/20°C for one week from sowing, and then placed under experimental conditions for a further week," after which "plant growth, gas exchange and CH4 emission rates were determined."
As for the results, first of all, the two researchers say they found "no detectable CH4 from [a] control treatment (without plant tissue), indicating that CH4 from the experimental treatments was emitted only from plant tissues." Second, they found that the plants grown under higher temperature and water stress emitted more CH4 than those grown under lower temperature and no water stress. And third, they found that "elevated CO2 had the opposite effect," so that it "partially reverses" the effects of the other two factors.
Qaderi and Reid conclude that "although rising atmospheric CO2 reduces plant CH4 emissions, it may not fully reverse the effects of temperature and drought," which they assume will increase in tandem with the ongoing rise in the air's CO2 content. Nevertheless, this result is still a positive finding. In addition, it may well be much more positive than they make it out to be, especially if temperatures and drought do not increase with the passage of time and continued increases in the air's CO2 content, which many -- such as us -- believe to be a real possibility, in that (1) droughts have not been shown to be more prevalent worldwide in warmer as opposed to colder periods of earth's history, and (2) due to the natural oscillatory behavior of earth's surface air temperature on millennial timescales -- which over the past two millennia has successively brought us the last phase of the Roman Warm Period, the Dark Ages Cold Period, the Medieval Warm Period, the Little Ice Age, and the initial phase of the Current Warm Period -- it will likely not warm much more than it has already warmed before the globe's mean surface air temperature plateaus out and ultimately begins a slow decline to a cooler state, aided by the ever-increasing CO2-induced reduction in aerobic plant CH4 emissions.
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