Environmental influences on the maximum quantum yield of terrestrial primary production

Historically, terrestrial biosphere models (TBMs) have assigned the intrinsic (maximum) quantum yield of photosynthesis ( ${\varphi }_0)$ a constant value for each plant functional type. However, experimental studies have shown that ${\varphi }_0$ - when measured on light-adapted leaves - depends on temperature. It is unclear whether this dependence is universal or biome-specific; how it is manifested at the ecosystem level; and how it should be represented in TBMs. By fitting empirical light-response curves to a global set of eddy-covariance CO₂ flux measurements and correcting for photorespiration, we inferred apparent, ecosystem-level ${\varphi }_0$ values and their temperature responses across a wide range of environments. The temperature response of the apparent ecosystem-level ${\varphi }_0$ follows a universal bell-shaped curve. The shape of this curve does not markedly differ among biomes, but the maximum value of ${\varphi }_0$ decreases with increasing aridity, its temperature optimum increases with increasing growth temperature, and its sensitivity to temperature increases as growth temperature declines. Our model for ${\varphi }_0\left(T\right)$ aligns with recent theory highlighting the role of cytochrome b₆f in regulating the light reactions of photosynthesis. If implemented in TBMs, this model should allow better predictions of the responses of terrestrial ecosystem function to a warming climate.