The Influence of Temperature on Photosynthesis and Transpiration in ten Temperate Grass Varieties Grown in four Different Environments

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Abstract
The influence of temperature on photosynthesis and transpiration was studied in ten varieties of Lolium perenne, L. multiflorum, Dactylis glomerata, and Festuca arundinacea from three climatic origins grown in three different controlled environments (15 °C, 72 W m-2 visible irradiation, 16-h photoperiod; 25 °C, 72 W m-2 visible irradiation, 16-h photoperiod; and 25 °C, 180 W m-2 visible irradiation, 16-h photoperiod) and in the glasshouse in July/August. The optimum temperature for photosynthesis was influenced primarily by growth environment; growth at low temperature (15 °C) resulted in a low optimum temperature, which differed little from variety to variety. The maximum CO2-exchange rate was influenced by growth environment and by variety. Within a variety, plants grown at higher light intensity or lower temperature had a greater CO2-exchange rate. Seven varieties showed a negative correlation between the optimum leaf temperature and the maximum CO2-exchange rate. Activation energies for photosynthesis were influenced by growth environment only. There were marked varietal differences in the values of leaf resistances (ra + rt) obtained from transpiration data at the optimum leaf temperature for CO2 exchange. In Lolium, and Dactylis the Mediterranean varieties had higher leaf resistances than the Northern varieties with the maritime varieties intermediate. In general the Dactylis varieties had higher resistances than the corresponding Lolium and Festuca varieties. Only at high growth temperatures was (ra+rl) insensitive to temperature; otherwise an activation energy of about 10 kcal/mole was observed. A negative correlation was found between mean varietal diffusion resistances (ra+rl), and corresponding maximum CO2-exchange rates.

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