C[O.sub.2] elicits long-term decline in nitrogen fixation

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From: Science(Vol. 304, Issue 5675)
Publisher: American Association for the Advancement of Science
Document Type: Article
Length: 850 words
Lexile Measure: 1640L

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Rising atmospheric carbon dioxide ([C.sub.a]) a product of fossil fuel burning, land-use change, and cement manufacture, is expected to cause a large carbon sink in land ecosystems, partly mitigating human-driven climate change (1). Increasing biological nitrogen fixation with rising C has been invoked as a means to provide the N necessary to support C accumulation (2). As in many short-term experiments (3), we found that C enrichment increased N fixation during the first year of treatment in an oak woodland. However, the effect declined and disappeared by the third year. Ca enrichment consistently depressed N fixation during the 5th, 6th, and 7th years of treatment. Reduced availability of the micronutrient molybdenum, a key constituent of nitrogenase, best explains this reduction in N fixation. Our results demonstrate how multiple element interactions can influence ecosystem responses to atmospheric change and caution against expecting increased biological N fixation to fuel terrestrial C accumulation.

We investigated the effects of elevated [C.sub.a] on legume N fixation in a stand of scrub-oak vegetation in central coastal Florida, where the leguminous vine Galactia elliottii Nutt. occurs naturally (4). During the first year of the experiment, elevated [C.sub.a] nearly doubled N fixation by G. elliottii (Fig. 1A), but this effect disappeared and later reversed ([C.sub.a] X time interaction, P =...

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Gale Document Number: GALE|A118183638