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Effects of Elevated CO2 on Legume Nitrogen Fixation in a Grassland Ecosystem
Lee, T.D., Reich, P.B. and Tjoelker, M.G.  2003.  Legume presence increases photosynthesis and N concentrations of co-occurring non-fixers but does not modulate their responsiveness to carbon dioxide enrichment.  Oecologia 10.1007/s00442-003-1309-1.

What was done
As part of a long-term grassland FACE experiment, the authors grew the N2-fixing legume Lupinus perennis L. in monoculture and in nine-species plots at ambient and enriched (to 560 ppm) atmospheric CO2 concentrations.

What was learned
The proportion of Lupinus N derived from symbiotic N2 fixation increased from 44% to 57% in monoculture (43% to 54% in nine-species plots), which combined with the CO2-induced increases in plant biomass production resulted, in the words of the authors, "in a doubling of N fixed per plot (g fixed N m-2) under elevated compared to ambient CO2."

What it means
In a CO2-enriched world of the future, legumes like Lupinus will likely provide the ecosystems within which they occur with considerably more nitrogen than is currently available to them, which should enhance the ability of co-occurring species to grow and develop to their fullest potential if they are currently inhibited from doing so by a lack of available soil N.

Reviewed 15 October 2003