© 2007 Heron Publishing—Victoria, Canada
Inhibition and acclimation of C3 photosynthesis to moderate heat: a perspective from thermally contrasting genotypes of Acer rubrum (red maple)
David J. Weston (1, 2) and William L. Bauerle (3, 4)
1. Oak Ridge National Laboratory, Environmental Sciences Division, Oak Ridge, TN 37831-6422, USA / 2. Corresponding author (westondj@ornl.gov) / 3. Clemson University, Department of Horticulture, Clemson, SC 29634, USA / 4. Clemson University, Department of Forestry and Natural Resources, Clemson, SC 29634, USA / Received May 19, 2006; accepted September 11, 2006; published online May 1, 2007
Summary
Effects of moderate heat on growth and photosynthesis were investigated in two clonal genotypes of Acer rubrum L., originally collected from the thermally contrasting habitats of Florida and Minnesota, USA, and known in the horticultural
trade for sensitivity and insensitivity to heat, respectively. Under both common garden and warm greenhouse conditions (day/night
temperature of 33/25 °C), the Florida genotype exhibited more growth than the Minnesota genotype. To determine the physiological
parameters associated with this response, plants were acclimated to ambient (27/25 °C) or moderately elevated (33/25 °C) temperatures
for 21 days before measurement of net photosynthesis at temperatures ranging from 25 to 48 °C. In vivo measurements of gas
exchange and chlorophyll a fluorescence of ambient-acclimated plants revealed that, compared with the Minnesota genotype,
the Florida genotype maintained a higher photosynthetic rate, higher stomatal conductance, more open PSII reaction centers,
a greater PSII quantum yield and a lower quantum requirement for photosystem II (ΦPSII) per mole of CO2 fixed (ΦCO2) throughout the measurement temperature range. When both genotypes were acclimated at 33/25 °C and measured at 33 °C, analysis
of the response of net photosynthesis to calculated intercellular CO2 concentration indicated that the maximal rate of Rubisco carboxylation (Vcmax) decreased more in the Minnesota genotype than in the Florida genotype in response to elevated temperature. Additionally,
ΦPSII/ΦCO2 at 33 °C was markedly higher for Minnesota plants under photorespiratory conditions, but similar to Florida plants under
non-photorespiratory conditions. The results indicate that the higher net photosynthetic rate at 33/25 °C of the Florida genotype
compared with the Minnesota genotype could be a result of several mechanisms, including the maintenance of a higher Vcmax and a more efficient quantum requirement of PSII per mole of CO2 fixed, which is likely the result of lower photorespiration.
Keywords:
drummondii, genotypic variation, temperature inhibition.
