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Elevated CO2 enhances resprouting of a tropical savanna tree

Hoffmann WA, FA Bazzaz, NJ Chatterton, PA Harrison, RB Jackson
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The savannas (cerrado) of south-central Brazil are currently subjected to frequent anthropogenic burning, causing widespread reduction in tree density. Increasing concentrations of atmospheric CO2 could reduce the impact of such frequent burning by increasing the availability of nonstructural carbohydrate, which is necessary for resprouting. We tested the hypotheses that elevated CO2 stimulates resprouting and accelerates replenishment of carbohydrate reserves. Using a factorial experiment, seedlings of a common Brazilian savanna tree, Keilmeyera coriacea, were grown in 350 ppm and 700 ppm CO2 and in two nutrient levels. To simulate burning, the plants were either clipped at 15 weeks or were left unclipped. Among unclipped plants, CO2 and nutrients both stimulated growth, with no significant interaction between nutrient and CO2 effects. Among clipped plants, both CO2 and nutrients stimulated resprouting. However, there was a strong interaction between CO2 and nutrient effects, with CO2 having a significant effect only in the presence of high nutrient availability. Under elevated CO2, carbohydrate reserves remained at higher levels following clipping. These results indicate that under elevated CO2 this species may be better able to endure the high frequency of anthropogenic burning in the Brazilian savannas.

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