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Response of a Tropical Legume Tree to Elevated CO2
Aidar, M.P.M., Martinez, C.A., Costa, A.C., Costa, P.M.F., Dietrich, S.M.C. and Buckeridge, M.S.  2002.  Effect of atmospheric CO2 enrichment on the establishment of seedlings of jatoba, Hymenaea courbaril L. (Leguminosae, Caesalpinioideae).  Biota Neotropica 2 (1):

Aidar et al. note that the leguminous Hymenaea courbaril L. tree, commonly known as jatoba, which grows to a height of 20-30 meters with a trunk diameter of 200 cm, is "a late secondary/climax species that is one of the most important trees in mature tropical forests of the Americas."  They say it occurs "in more than 30% of 43 inventories made in the extra-Amazonian riparian forests (Rodrigues and Nave, 2000)" and that it shows "wide distribution in [the] neotropics, from the Caribbean isles, Mexico and Peru to Southeastern Brazil (Allen and Allen, 1981)."

What was done
The authors sprouted and grew jatoba seedlings in pots placed within small open-top chambers maintained at atmospheric CO2 concentrations of 360 and 720 ppm within a shaded glasshouse (to simulate the low light regime at the forest floor where the seeds typically germinate) for a period of 70 days, over which time they measured rates of net photosynthesis in seedlings with and without cotyledons, which they removed from half of the plants.

What was learned
Aidar et al. report that "a marked and persistent increase (2 fold) in photosynthesis (CO2 assimilation) was observed in all cases (with or without cotyledons)," when the seedlings were exposed to elevated CO2.  In addition, they found that "plants grown under enriched CO2 did not acclimate," that is, they did not experience down regulation.  Also, they observed a 35% increase in the water use efficiency of the seedlings.

What it means
In the words of the authors, "under the climatic conditions forecasted on the basis of the present carbon dioxide emissions, Hymenaea courbaril should establish faster in its natural environment and might also serve as an efficient mechanism of carbon sequestration within the forest."  In addition, they note that the CO2-induced increase in water use efficiency may enable jatoba "to tolerate dryer and more open environments, which should allow them to better cope with drought stress or a more seasonal climate."  Last of all, they say that the jatoba tree would likely exhibit similar positive responses to even greater emissions of CO2, for they note that light-saturated photosynthesis in jatoba seedlings continued to rise in response to increasing atmospheric CO2 concentrations well above 1,000 ppm.  What is more, they say they "have measured the saturation level of some other tropical trees from the rain forest (Caesalpinia echinata, Piptadenia gonoacantha, Tibouchina granulose, T. pulchra) and all of them [also] saturate at relatively high CO2 concentrations."  Hence, it is likely that neotropical forests in general are suited to much higher-than-present atmospheric CO2 concentrations and would fare far better than they do today in a CO2-enriched world of the future.

Allen, O.N. and Allen, E.K.  1981.  The Leguminosae.  The University of Wisconsin Press, Madison, Wisconsin, USA, pp. 337-338.

Rodrigues, R.R. and Nave, A.G.  2000.  Heterogeneidade floristica das matas ciliares.  In: Rodrigues, R.R. and Leitao Filho, H.F. (Eds.) Matas Ciliares: Conservacao e Recuperacao.  Editora da USP/FAPESP, 2000.  Sao Paulo, Brazil, pp. 45-71.

Reviewed 12 May 2004