Changes in the Responses of Leaf Gas Exchange to Temperature and Photosynthesis Model Parameters in Four C<sub>3</sub> Species in the Field
2025
James Bunce
Substantial variation in the temperature dependence of parameters of the Farquhar, von Caemmerer, and Berry C<sub>3</sub> photosynthesis model, as well as those of in vitro Rubisco kinetic characteristics, have been observed in controlled conditions but have seldom been systematically examined in the field. In this work, A vs. C<sub>i</sub> curves were measured over a 15 or 20 °C range of temperature in four C<sub>3</sub> species growing outdoors on two occasions about three weeks apart early in the growing season and also once near mid-season when air temperatures were more stable. The two early season occasions were chosen for having contrasting temperatures for 3 to 4 days preceding the measurements. Low temperatures (mean maximum/minimum temperatures of 19/11 °C) resulted in higher values of the V<sub>Cmax</sub> of Rubisco and J<sub>max</sub> at a given measurement temperature in most species compared with higher temperatures (max/min 31/25 °C). The apparent activation energy of V<sub>Cmax</sub> of Rubisco ranged from 56 to 82 kJ mol<sup>−1</sup>, and that of electron transport (J<sub>max</sub>) ranged from 28 to 56 kJ mol<sup>−1</sup> across species and temperatures. In three of the four species, the activation energy of V<sub>Cmax</sub> decreased and that of J<sub>max</sub> increased after the cooler temperatures. Stomatal conductance measured at 20 and 25 °C increased strongly with the prior warm temperatures in all species. Measurements made near mid-season, after a period of relatively stable temperatures (mean maximum/minimum temperatures of 27/18 °C), also indicated a wide range of values of the activation energies of V<sub>Cmax</sub> and J<sub>max</sub> among these species.
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