Temperature effects on the global patterns of photosynthetic quantum efficiency

Abstract

The photosynthetic quantum efficiency (φ0) is a key input parameter for modelling gross primary productivity in terrestrial biosphere models. Historically, these models assumedφ0to be constant, based on leaf measurements under unstressed conditions and within a narrow temperature range. However, increasing evidence suggests a temperature-dependentφ0on temperature, though it remains unclear whether this response is generalized or if it propagates to the ecosystem. Here, we derivedφ0(T) at the ecosystem level for sites distributed globally, using sub-daily eddy covariance measurements of CO2exchange and above/below-canopy measurements of photosynthetic flux density to derive the fraction of absorbed photosynthetically active radiation (fAPAR). We found thatφ0(T) shows a consistent bell-shaped response curve with temperature in all the sites we analysed. These patterns held when analysed with a larger global dataset using remotely sensed fAPAR. Furthermore, we observed that the values ofφ0(T) are not markedly different among biomes, instead, there is a gradual transition of the peakφ0(T) which decreases following an aridity gradient. Additionally, we noted varying sensitivity to temperature among the different sites, with sensitivity increasing as growth temperature decreases.