Abstract
Since most conifer species are commonly distributed in low-temperature regions, information of the photosynthetic response to temperature of conifers growing in high-temperature regions is little known. In order to obtain information on the photosynthetic response of conifers to global warming, the photosynthetic responses of 7 conifers grown from low to high elevations in subtropical Taiwan to both growth and measurement temperatures were studied. The results indicated that plants, except Chamaecyparis obtusa var. formosana, grown at high temperatures (30/23℃, day/ night), exhibited lower inhibition of the light-saturated photosynthetic rate (PN) at high temperature and an increase in the optimum temperature for photosynthesis (Topt). The Topt values of conifers with low- and high-elevational distributions grown at low temperatures (20/10℃) were 20~23 and 16~21℃, respectively; and Topt values of these conifers grown at high temperatures were 23~27 and 21℃, respectively. Differences in Topt values for 3 conifers (Nageia nagi, Podocarpus macrophyllus, and Calocedrus macrolepis var. formosana) with low-elevation (< 1000~1900 m) distributions, and 1 conifer (Pinus taiwanensis) with a broad-elevational (750~3000 m) distribution with low- and high-temperature acclimation were 2.2~7.7℃; those for 2 conifers with high-elevational distributions (Cha. formosensis and Cha. obtusa var. formosana, 1000~2900 m) were -0.7~2.3℃. In addition, 1 species with a high-elevational distribution (Tsuga chinensis var. formosana, 2000~3500 m) grown at low temperatures, and 1 species (P. taiwanensis) with a broad elevational distribution grown at high-temperatures both maintained relatively high PN values (≥ 90% of the maximum) at wide temperature ranges (8~24 and 18~34℃, respectively). From the above results it was concluded that, just like broadleaf evergreen trees, the photosynthesis of conifer plants distributed at low and high elevations in Taiwan adapts to the temperature of their habitat through both genetic variations and thermal acclimation. Conifers with low- and broad-elevational distributions generally exhibited a higher potentiality for thermal acclimation of the Topt when growth temperatures shifted from low to high.