Plants differ in how much the response of net photosynthetic rate
(PN) to temperature (T) changes with the T during leaf development, and also in the biochemical basis of such changes in response. The amount of photosynthetic acclimation to T and the components of the photosynthetic system involved were compared in Arabidopsis thaliana and Brassica oleracea to determine how well A. thaliana might serve as a model organism to study the process of photosynthetic acclimation to T. Responses of single-leaf gas exchange and chlorophyll fluorescence to CO2 concentration measured over the range of 10-35 °C for both species grown at 15, 21, and 27 °C were used to determine the T dependencies of maximum rates of carboxylation (VCmax), photosynthetic electron transport (Jmax), triose phosphate utilization rate (TPU), and mesophyll conductance to carbon dioxide (g'm). In A. thaliana, the optimum T of PN at air concentrations of CO2 was unaffected by this range of growth T, and the T dependencies of VCmax, Jmax, and g'm were also unaffected by growth T. There was no evidence of TPU limitation of PN in this species over the range of measurement conditions. In contrast, the optimum T of PN increased with growth T in B. oleracea, and the T dependencies of VCmax, Jmax, and g'm, as well as the T at which TPU limited PN all varied significantly with growth T. Thus B. oleracea had much a larger capacity to acclimate photosynthetically to moderate T than did A. thaliana.
Diurnal courses in net photosynthetic rate (PN), stomatal conductance (gs), leaf water potential (ψ), internal CO2 concentration (ci), and water use efficiency (WUE) were studied as season progressed, in relation to environmental factors in field grown Prunus amygdalus. In sun leaves PN reached maximum between 09:00 to 11:00 h and subsequently declined when high temperature and low humidity occurred. An increase was observed late in the afternoon. A decrease in gs and ψ was found as season progressed in both years of measurements. In periods of high evaporative demand, ψ was very low, however, it did not explain the reductions of PN in all the three periods (spring, early and late summer). Midday depression of PN and gs seemed to be related with leaf temperature (Tl) and high irradiance. Increase in ci and F0 and decrease in Fv/Fm found between 12:00 and 14:00 h corresponded to the decrease in PN. Therefore, a transient modification of photosynthetic machinery might be considered. WUE was negatively correlated with vapour pressure difference of leaf to air, that decreased during the day. The September values, higher than in the previous months, were due to the lower seasonal decreases in PN than in gs. and M. C. Matos ... [et al.].