Effect of CO₂‐enrichnient on seedling physiology and growth of two tropical tree species

Seedlings of two tree species from the Atlantic lowlands of Costa Rica, Ochroma la-gopus Swartz, a fast-growing pioneer species, and Pentaclethra macroloba (Willd.) Kuntze, a slower-growing climax species, were grown under enriched atmospheric CO2 in controlled environment chambers resulting in significant increases in water use efficiency.

Abstract

Seedlings of two tree species from the Atlantic lowlands of Costa Rica, Ochroma la‐gopus Swartz, a fast‐growing pioneer species, and Pentaclethra macroloba (Willd.) Kuntze, a slower‐growing climax species, were grown under enriched atmospheric CO 2 in controlled environment chambers. Carbon dioxide concentrations were maintained at 350 and 675 μl 1 −1 under photosynthetic photon flux densities of 500 μol m −2 s −1 and temperatures of 26°C day and 20°C night. Total biomass of both species increased significantly in the elevated CO 2 treatment; the increase in biomass was greatest for the pioneer species, O. lagopus . Both species had greater leaf areas and specific leaf weights with increased atmospheric CO 2 . However, the ratio of non‐pho‐tosynthetic tissue to leaf area also increased in both species leading to decreased leaf area ratios. Plants of both species grown at 675 μl 1 −1 CO 2 had lower chlorophyll contents and photosynthesis on a leaf area basis than those grown at 350 μl 1 −1 . Reductions in net photosynthesis occurred despite increased internal CO 2 concentrations in the CO 2 ‐enriched treatment. Stomatal conductances of both species decreased with CO 2 ‐enrichment resulting in significant increases in water use efficiency.