Plant responses to volcanically elevated CO 2 in two Costa Rican forests

Abstract. We explore the use of active volcanoes to determine the short- and long-term effects of elevated CO 2 on tropical trees. Active volcanoes continuously but variably emit CO 2 through diffuse emissions on their flanks, exposing the overlying ecosystems to elevated levels of atmospheric CO 2 . We found tight correlations ( r 2 =0.86 and r 2 =0.74 ) between wood stable carbon isotopic composition and co-located volcanogenic CO 2 emissions for two of three investigated species ( Oreopanax xalapensis and Buddleja nitida ), which documents the long-term photosynthetic incorporation of isotopically heavy volcanogenic carbon into wood biomass. Measurements of leaf fluorescence and chlorophyll concentration suggest that volcanic CO 2 also has measurable short-term functional impacts on select species of tropical trees. Our findings indicate significant potential for future studies to utilize ecosystems located on active volcanoes as natural experiments to examine the ecological impacts of elevated atmospheric CO 2 in the tropics and elsewhere. Results also point the way toward a possible future utilization of ecosystems exposed to volcanically elevated CO 2 to detect changes in deep volcanic degassing by using selected species of trees as sensors.