Thermal acclimation of leaf photosynthetic traits in an evergreen woodland, consistent with the coordination hypothesis

Fürstenau Togashi, Henrique; Prentice, Iain Colin; Atkin, Owen K.; Macfarlane, Craig; Prober, Suzanne M.; Bloomfield, Keith J.; Evans, Bradley John

Ecosystem models commonly assume that key photosynthetic traits, such as carboxylation capacity measured at a standard temperature, are constant in time. The temperature responses of modelled photosynthetic or respiratory rates then depend entirely on enzyme kinetics. Optimality considerations, however, suggest this assumption may be incorrect. The “coordination hypothesis” (that Rubisco- and electron-transport-limited rates of photosynthesis are co-limiting under typical daytime conditions) predicts, instead, that carboxylation (inline-formulaVcmax) capacity should acclimate so that it increases somewhat with growth temperature but less steeply than its instantaneous response, implying that inline-formulaVcmax when normalized to a standard temperature (e.g. 25 inline-formulaC) should decline with growth temperature. With additional assumptions, similar predictions can be made for electron-transport capacity (inline-formulaJmax) and mitochondrial respiration in the dark (inline-formulaRdark). To explore these hypotheses, photosynthetic measurements were carried out on woody species during the warm and the cool seasons in the semi-arid Great Western Woodlands, Australia, under broadly similar light environments. A consistent proportionality between inline-formulaVcmax and inline-formulaJmax was found across species. inline-formulaVcmax, inline-formulaJmax and inline-formulaRdark increased with temperature in most species, but their values standardized to 25 inline-formulaC declined. The inline-formulaci:ca ratio increased slightly with temperature. The leaf N inline-formula: P ratio was lower in the warm season. The slopes of the relationships between log-transformed inline-formulaVcmax and inline-formulaJmax and temperature were close to values predicted by the coordination hypothesis but shallower than those predicted by enzyme kinetics.



Fürstenau Togashi, Henrique / Prentice, Iain Colin / Atkin, Owen K. / et al: Thermal acclimation of leaf photosynthetic traits in an evergreen woodland, consistent with the coordination hypothesis. 2018. Copernicus Publications.


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