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Breathing easier about plant biodiversity

Rising levels of carbon dioxide threaten many things on this planet, but plant biodiversity may not be one of them, according to results of a 10-year experiment by University of Minnesota scientist Peter Reich.

By some estimates, rising CO2 levels had been expected to clip diversity by 30 percent or more. This study throws a question mark into those worst-case global warming scenarios for at least the plant species studied. It does not erase concern, however, for the impact on plants from potential changes in temperature, water levels and rainfall patterns.

In fact, rising CO2 may actually help counteract losses of diversity from another environmental villain: the global rain of nitrogen from fertilizers and exhaust fumes, according to the study which also is reported in Science this week.

In the experiment, 16 different species of plants were tested in 48 outdoor plots using ambient and elevated levels of nitrogen and carbon dioxide. Researchers measured the number of species observed in each plot and the mass of the plants both above and below ground, as well as factors related to soil, water and light that might affect plant growth.

Over time, the diversity of plants growing in the research plots changed significantly, depending on the combinations of plants and the way added CO2 and nitrogen affected the health of different species.

Pollution in the air set the plants back considerably. But one of the study’s key findings is that adding more CO2 to the mix cut the damage by half.

Reich, a Regents professor in the department of forest resources, made a point of being the first to say his study should not subtract from overall concern about C02 levels. He issued a statement, saying: "While it is a relief to find out that rising CO2 and nitrogen together may not directly cause enormous losses of diversity, any loss of diversity is troubling, and in any case, this finding does not detract from the urgent need for us to curb CO2 emissions given the other critical CO2 effects, such as overheating the planet and threatening marine life through ocean acidification."

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