Altitudinal Variation in the Photosynthetic Characteristics of Snow Gum, Eucalyptus pauciflora Sieb. ex Spreng. VI. Comparison of Field and Phytotron Responses to Growth Temperature

Abstract

A procedure for estimating field photosynthetic temperature optima from phytotron temperature response data, for elevational populations of E. pauciflora, is developed. It utilizes the principle that each population has a preferred temperature, Tpref, and an acclimation coefficient, α, which can be determined from phytotron-derived temperature response curves, and which enable the photosynthetic temperature optimum observed in a particular field temperature regime (Test) to be estimated from the expression Test = Tpref - α(Tpref - Tequiv), where Tequiv is a field temperature equivalent, in terms of its effect on the photosynthetic temperature optimum, to a known phytotron growth temperature. Application of the procedure to sets of field and greenhouse data suggests that when Tpref and α are based on phytotron day growth temperatures, and when Tequiv is based on the proposition that a square-wave conversion of the field day-time temperature curve is equivalent to the phytotron day growth temperature, estimates of field and greenhouse temperature optima can be made which give good agreement with observed values. The agreement is best when active, current-year tissue is used as a basis of the field observations and when single leaves rather than shoots are used for field measurements. The procedure is also used to compare actual rates of net photosynthesis, Pamb, obtained from field and phytotron studies, when both are plotted against equivalent temperature. Using this procedure, the large apparent differences between rates of net photosynthesis observed in the field and in the phytotron can be considerably reduced. This suggests that the notion of equivalent temperature may provide a useful means of minimizing the effects of physical, temperature-related differences in comparing field and phytotron responses, thereby widening the range of practical applications of phytotron experiments.

Physiological regulation of productivity and water use in Eucalyptus: a review

“…In E. pauciflora (Slatyer and Morrow, 1977), and to some extent in E. nitens (Battaglia et al, 1996), increases in seasonal temperatures were associated with increases in A, but this was not observed in E. globulus (Battaglia et al, 1996). The photosynthetic rate of E. pauciflora declined with site elevation (Slatyer and Morrow, 1977), a characteristic that may be associated with environments where photosynthesis is mainly temperature limited (Slatyer, 1977): no differences were found between populations of E. globulus (Battaglia et al, 1996).…”

“…This finding indicates that species from a continental climate and a more variable diurnal temperature range (E. nitens) utilise a broad temperature maximum to maximise carbon uptake, whereas species from a coastal environment where diurnal changes in temperature are moderate (E. globulus) maximise carbon uptake by having a dynamic response to changes in temperature. E. pauciflora (a ¼ 0:34; Slatyer, 1977) is similarly from a continental climate. In all species, the temperature optimum for photosynthesis increases and decreases in response to seasonal changes in ambient temperature.…”

“…As photosynthesis is a temperature-dependent process, for many species, including Eucalyptus, the response curve is typically parabolic (Slatyer, 1977;Säll and Petterson, 1994;Battaglia et al, 1996). Seasonal shifts in temperature result in adaptive changes that are defined by the slope (a) of the line relating the optimum temperature for photosynthesis and the acclimation temperature.…”

Effects of day and night temperature and temperature variation on photosynthetic characteristics

“…The shift of the optimum temperature for net photosynthesis in Eucalyptus pauciflora [7] results primarily from a shift in the response of stomatal conductance to temperature [8], rather than than in mesophyU photosynthetic characteristics. Therefore the correlation of the optimum temperature with the day temperature in this species is not directly comparable to the responses found in this study.…”

“…In Fragaria vesca, a 10°C difference between day and night temperature increased net photosynthetic rates at all temperatures and lowered the optimum temperature for photosynthesis, but a 20°C difference in temperature gave intermediate absolute rates, and raised the optimum temperature for photosynthesis [2]. In Eucalyptus pauciflora the optimum temperature for net photosynthesis was correlated with the average temperature during the light period [7]. In none of these studies was the response determined to constant temperfitures equal to all day and night temperatures used.…”