Flo, V. | Search bioRxiv

bioRxiv2023

Temperature effects on the global patterns of photosynthetic quantum efficiency

SummaryO_LIHistorically, 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. C_LIO_LIBy 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}0values and their temperature responses across a wide range of environments. C_LIO_LIThe temperature response of 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. C_LIO_LIOur model for {varphi}0(T) 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. C_LI

ecology↗

bioRxiv2023

Incorporating photosynthetic acclimation improves stomatal optimisation models

Stomatal opening in plant leaves is regulated through a balance of carbon and water exchange under different environmental conditions. Accurate estimation of stomatal regulation is crucial for understanding how plants respond to changing environmental conditions, particularly under climate change. A new generation of optimality-based modelling schemes determines instantaneous stomatal responses from a balance of trade-offs between carbon gains and hydraulic costs, but most such schemes do not account for biochemical acclimation in response to drought. Here, we compare the performance of seven instantaneous stomatal optimisation models with and without accounting for photosynthetic acclimation. Using experimental data from 38 plant species, we found that accounting for photosynthetic acclimation improves the prediction of carbon assimilation in a majority of the tested models. Non-stomatal mechanisms contributed significantly to the reduction of photosynthesis under drought conditions in all tested models. Drought effects on photosynthesis could not accurately be explained by the hydraulic impairment functions embedded in the stomatal models alone, indicating that photosynthetic acclimation must be considered to improve estimates of carbon assimilation during drought. Summary StatementAccounting for photosynthetic acclimation improves the predictions of carbon assimilation in all the stomatal optimization models evaluated. The influence of drought on photosynthesis cannot be fully explained by the hydraulic impairment function of the stomatal models alone.

biophysics↗