Effects of low temperature acclimation on photosynthesis in three Chilean Proteaceae
Embothrium coccineum, Gevuina avellana, and Lomaría ferruginea grow in habitats contrasting in temperature and light intensity. Embothrium coccineum is a pioneer species that establishes itself in open sites completely exposed to variable sunlight and temperature. Gevuina avellana is usually found in more protected sites. Lomaría ferruginea regenerates under the canopy in sites with low thermal oscillations and high humidity. In order to establish an association of their habitats with functional attributes of each species, we studied their photosynthetic responses to temperature and light intensity. We expected that E. coccineum, which grows at full sun, is able to acclimate much better its photosynthetic apparatus to different temperatures than the shade tolerant L. ferruginea and the semi-shade tolerant G. avellana. One group of plants of each species containing six individuals each was subjected to 4 °C (cold-acclimated plants). Another group with the same number of individuals was subjected to 20 °C (non-acclimated plants). In non-acclimated plants of E. coccineum, the photosynthetic rate as measured by 0(2) evolution presented its maximum at 30 °C (16.5 ^mol 0(2) m"² s"¹) with an optimum between 20 and 35 °C, while in G. avellana and L. ferruginea the highest photosynthetic rate (~13 ^mol 0(2) m"² s") was obtained at 25 °C. Cold acclimation significantly reduced the photosynthetic rates of the investigated species. The Q10 for 0(2) evolution decreased significantly in cold-acclimated E. coccineum and G. avellana but not in L. ferruginea. The fluorescence parameters of PSII showed that E. coccineum presents a higher effective quantum yield (cPPSII) at both growth temperatures. Photochemical quenching (qP) was more affected by the photosynthetic photon flux density (PPFD) in L. ferruginea than in the other species. Lomaría ferruginea presented the highest non-photochemical quenching (NPQ) at lower PPFD. Thus, the photosynthetic apparatus of each species presents functional differences according to the characteristics of light availability and temperature changes of their habitats.