Altitudinal Variation in the Photosynthetic Characteristics of Snow Gum, Eucalyptus pauciflora Sieb. ex Spreng. IV. Temperature Response of Four Populations Grown at Different Temperatures

Abstract

Photosynthetic temperature response curves were measured at leaf temperatures from 10 to 40°C on seedlings of E. pauciflora grown from seed collected at tree-line (elevation 1905 m) in the Snowy Mountains area and at three lower elevations, 915, 1215 and 1645 m, which correspond to those used in an earlier field study (Slatyer and Morrow 1977). The material was grown in naturally lit, temperature-controlled greenhouses at day/night temperatures of 8/4, 15/10, 21/16, 27/22 and 33/28°C. Comprehensive measurements were made on the tree-line population, in which peak rates of net photosynthesis, Pamb, reached 75 ng cm-2 s-1 at a temperature of 20�°C, from material grown at 21/16°. Minimum levels of intracellular resistance, rt, were 2.8 s cm-1, and of leaf gas-phase resistance to CO2 transfer, r1, were 3.2 s cm-1. Changes in rt and r1, with measurement temperature, appeared to be of approximately equal importance in mediating the overall photosynthetic temperature response. Changes in the CO2 compensation point, Γ were of increasing importance at higher measurement temperatures. The photosynthetic temperature optimum was markedly affected by the growth temperature regime. In the tree-line population, it increased from about 16° when grown at 8/4° to 24° when grown at 33/28°. The relationship between the observed photosynthetic temperature optimum and the day temperature of the growth regime indicated a preferred temperature for photosynthesis of 20.0°, and a tendency for the temperature optimum to shift by 0.34° per degree shift in the day growth temperature. A similar effect of growth temperature on the photosynthetic temperature optimum was noted in the three lower-elevation populations, in which preferred temperatures of 21.5, 24.2 and 27.2° were calculated for the material collected at 1645, 1215 and 915 m respectively. These temperatures were several degrees higher than the field-observed temperature optima, although the gradient of preferred temperature with elevation was comparable to that noted in the field study.

Local ecotypic and species range-related adaptation influence photosynthetic temperature optima in deciduous broadleaved trees

“…There is evidence that species or ecotypes growing in colder environment often but not always have lower photosynthetic temperature optima (T opt ) than those growing at higher temperatures (Björkman et al 1972;Fryer and Ledig 1972;Slatyer 1977;Berry and Björkman 1980;Cavieres et al 2000;Cunningham and Read 2002;Gunderson et al 2010). Taxa can be adapted to their different thermal origins and thus differ in T opt when they grow in a common environment (Berry and Björkman 1980;Cunningham and Read 2002;Gunderson et al 2010).…”

“…Such variation in T opt can be due to genetic differences in temperature optima (that would arise from adaptation to local thermal environments), physiological acclimation (i.e., phenotypic) to growth temperature, or both. Intra-specific differences in T opt of chamber-grown tree seedlings have been long noted among populations originating from different thermal environments (Björkman et al 1972;Fryer and Ledig 1972;Slatyer 1977). In some forest tree species interand intraspecific variation in T opt have been studied, but mostly in controlled conditions.…”

“…Based on evidence of strong ecotypic thermal adaptation of photosynthesis (Fryer and Ledig 1972;Slatyer 1977;Berry and Björkman 1980;Ishikawa et al 2007), we hypothesized that the A. rubrum and Q. rubra southern ecotypes adapted to warmer climates would show higher photosynthetic temperature optima than northern, cold adapted provenances. This would indicate that adaptation to the thermal conditions of origin would dominate over 10-year acclimation to common temperature in a common environment.…”

Phenotypic Plasticity in Photosynthetic Temperature Acclimation among Crop Species with Different Cold Tolerances

“…For example, the optimum temperature for photosynthesis differs between temperate evergreen species and tropical evergreen species (Hill et al, 1988;Read, 1990;Cunningham and Read, 2002). Such differences have been observed even among ecotypes of the same species (Bjö rkman et al, 1975;Pearcy, 1977;Slatyer, 1977).…”

“…Plants native to low-temperature environments and those grown at low temperatures generally exhibit higher photosynthetic rates at low temperatures and lower optimum temperatures, compared with plants native to high-temperature environments and those grown at high temperatures (Mooney and Billings, 1961;Slatyer, 1977;Berry and Bjö rkman, 1980;Sage, 2002;Salvucci and Crafts-Brandner, 2004b). For example, the optimum temperature for photosynthesis differs between temperate evergreen species and tropical evergreen species (Hill et al, 1988;Read, 1990;Cunningham and Read, 2002).…”