Poster: Ecophysiology
Abs #
43: Estimating photosynthetic light-use efficiency using the photochemical reflectance index under conditions of short-term elevated CO2 and low temperature
Recent studies have shown that the photosynthetic light-use efficiency (LUE), defined as mol CO2 fixed per mol photons absorbed, can be estimated using the photochemical reflectance index (PRI) - an optical indicator of xanthophyll cycle activity. However, considerable uncertainty remains as to the response of the PRI/LUE relationship to variation in environmental factors other than irradiance. In this study, changes in LUE, PSII photochemical efficiency (∆F/Fm') and PRI with short-term elevated CO2 and low temperature were examined in thirteen perennial species varying in photosynthetic capacity and foliage nitrogen content. As expected, short-term exposure to elevated CO2 greatly enhanced the net photosynthesis and LUE in all species, but did not affect either ∆F/Fm' or PRI. In contrast, both LUE and ∆F/Fm' were reduced by low temperature, accompanied by a reduction in PRI. Low temperature also caused a reduction in maximum PSII photochemical efficiency (Fv/Fm) - an indicator of photoinhibition. The changes in PRI and photosynthetic parameters indicate that the overall photosynthetic system (photochemistry and CO2 assimilation) is down-regulated in response to short-term low temperature, but not up-regulated to short-term elevated CO2. The PRI can thus be used as an optical indicator of LUE when exposed to short-term low temperature, but not when increased rates of photosynthesis occur in response to short-term elevated CO2. Under low temperature, although a single regression line between PRI and LUE can be fitted to the response of the group of species, it is also evident that species-specific responses occur. This suggests that precise estimation of LUE from PRI measurements may require concurrent measurement of physiological parameters.
