A simple method for testing leaf responses of tall tropical forest trees to elevated CO2.

The effects of atmospheric CO2 enrichment on mature trees in their natural environment are largely unknown. Here we present a new, and inexpensive technique which can be used in situ to address some key physiological questions related to the CO2 problem. Small, light-weight cups mounted on the lower side of rigid leaves at the top of tall tropical forest trees were supplied with CO2-enriched air derived from a low-technology air mixing device utilizing forest floor CO2 evolution. We present the scientific rationale for such field experiments, technical details, an assessment of potential cup artifacts and first results illustrating effects of elevated CO2 on stomata and carbohydrate accumulation in the canopies of mature trees.