Photosynthetic responses to temperature of two tropical rainforest tree species from Costa Rica

Annual mean temperature increases will cause alterations in many ecosystem processes, which affect plants given their physiological sensitivity to temperature. That is closely related with plant growing conditions, genotype and plasticity. We studied the photosynthetic responses to instantaneous temperature changes and functional leaf traits in two tropical tree species associated with different successional positions, Zygia longifolia (early successional) and Dipteryx oleifera (late successional), in the northern lowlands of Costa Rica. We found that D. oleifera had thicker leaves and lower stomatal density, but similar specific leaf area to Z. longifolia. Maximum photosynthetic rate (Amax) and maximum RuBP saturate rate of carboxylation were higher in Z. longifolia than in D. oleifera. At 37 °C, only Z. longifolia reduced Amax and water use efficiency (WUE). But D. panamensis presented more severe effects on the quantum yield, respiration and light compensation points. The temperature response curves showed a similar optimum temperature near 27 °C for both species. On the other hand, the low and high temperature compensation points were different, with D. oleifera showing a narrower range than Z. longifolia. As a whole, we found two different strategies to avoid temperature stress: one reducing WUE (Z. longifolia), and the other one increasing metabolic rates (D. oleifera). However, the ability to withstand stressful situations may, in a larger context, negatively affect ecosystem water and carbon fluxes. Also, functional plasticity in response to temperature changes may relatively affect the ecosystem by causing long-term variations in their representation within the complex diversity mosaic of their forest habitats.