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Photosynthetic Acclimation After Six Years of Free-Air CO2 Enrichment of a Loblolly Pine Forest
Crous, K.Y. and Ellsworth, D.S.  2004.  Canopy position affects photosynthetic adjustments to long-term elevated CO2 concentration (FACE) in aging needles in a mature Pinus taeda forest.  Tree Physiology 24: 961-970.

What was done
Photosynthetic measurements were made of different-age needles at different crown positions on 19-year-old (in 2002) loblolly pine trees at the Duke Forest FACE facility (where the CO2-enriched trees are exposed to air containing an extra 200 ppm CO2) in the sixth year of a long-term study, after which the results were compared with the results of similar measurements made over the prior five years.

What was learned
Although there was "some evidence of moderate photosynthetic down-regulation ? in 1-year-old needles across the fifth to sixth year of CO2 exposure," the authors report that "strong photosynthetic enhancement in response to elevated CO2 (e.g., +60% across age classes and canopy locations) was observed across the years."  This long-term response, which roughly equates to a 90% (or just slightly smaller) growth enhancement for a 300 ppm increase in the air's CO2 content, is of about the same magnitude as the CO2-induced increase in wood and fruit production experienced over the past ten years of Idso and Kimball's long-term (17-plus years) sour orange tree experiment (see our Editorial of 5 Mar 2003).

What it means
More than one long-term study is now beginning to demonstrate that the positive effects of atmospheric CO2 enrichment on earth's woody plants may perhaps be maintained indefinitely, which bodes extremely well for all components of the biosphere that will live in the high-CO2 world of the future that grows ever closer with each passing day.

Reviewed 1 December 2004