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The universal rule linking plant metabolism to nitrogen can also assist efforts to measure the global carbon cycle. Through the process of photosynthesis, plants absorb and store more carbon dioxide than they emit through respiration. But global plant respiration is a huge variable that must be taken into account.

"If we estimate the nitrogen content of plants, we can model their metabolic rates, helping us to better assess the global plant metabolic rate," said Reich, a professor in the university's College of Natural Resources. "The amounts of carbon dioxide given off by plants is one of the weak spots in models of global carbon cycling."

To predict how fast atmospheric carbon dioxide will rise in the future, it is important to know all the sources that emit the gas and all the sources that soak it up. The amount of carbon dioxide in the atmosphere is well known, as is the rate of emissions from fossil fuel burning. The rate of photosynthesis, in which carbon dioxide is absorbed and stored as plant tissue, is difficult to measure but can be estimated globally from satellites, based on the visible plant cover. The plant cover indicates how much light the plants will intercept. Even harder to calculate are the global amounts of carbon dioxide released by living, respiring plants; the amounts released as plants are decomposed by microbes; and the amounts being absorbed and emitted by oceans.

"If all the carbon dioxide emitted from fossil fuel burning were to stay in the atmosphere, its rate of accumulation in the atmosphere would be two-and-a-half times as fast as it actually is and climate would change two-and-a-half times faster," said Reich. "Therefore, somewhere there's a 'fantastically important global carbon sink' that's soaking up 6
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Source:University of Minnesota