Estimating photosynthetic light‐use efficiency using the photochemical reflectance index: the effects of short‐term exposure to elevated CO₂ and low temperature

Abstract

There is growing interest in using the photochemical reflectance index (PRI) to estimate photosynthetic light‐use efficiency (LUE) in studies of terrestrial carbon exchange. However, evidence suggests that the PRI is correlated with LUE only while there is coordinated adjustment between PSII (photosystem II) photochemical efficiency (ΔF/F_m′) and the CO₂ fixation rate. The range of environmental conditions under which this occurs has yet to be fully explored. In this study we examined for 13 species the response of ΔF/F_m′, LUE, and the PRI to short‐term exposure to elevated CO₂ and low temperature. The PRI was linearly correlated with both ΔF/F_m′ and LUE under all conditions. Under elevated CO₂, LUE was considerably enhanced without significantly affecting either ΔF/F_m′ or the PRI. This is consistent with current mechanistic understanding of the basis of the PRI/LUE relationship. In contrast, ΔF/F_m′, LUE, and the PRI were on average reduced proportionally by low temperature. This suggests simple multiplicative scaling may be sufficient to account across species for the effect of typical diurnal temperature variations in PRI/LUE relationships.

Acknowledgements

This study was supported by a post‐doctoral fellowship provided by the New Zealand Foundation for Research, Science and Technology, under contract LCRX0202. We thank the New Zealand National Climate Laboratory (NZNCL) for providing the facilities used to conduct this study. We also thank Ted Pinkney and Cara Norling for technical assistance.