The temperature response of photosystem II quantum yield is an important driver of leaf photosynthesis: a review and data synthesis

Photosystem II quantum yield (φ_PSII) measures the efficiency with which photosystem II converts absorbed light to photochemistry, and thus variation in φ_PSII directly affects leaf CO₂ assimilation. Given the sensitivity of photosystem II to temperature stress, increasing our understanding of the φ_PSII temperature response could improve model estimates of terrestrial carbon cycling in an increasingly warm and erratic climate. We reviewed the literature to establish what is known of the φ_PSII temperature response and highlighted potential underlying physiological and molecular mechanisms. We then used φ_PSII temperature response data collated from our review to generate a new and improved temperature response function for φ_PSII. After examining how a subset of land surface models currently represent φ_PSII and its temperature response, we incorporated our new temperature response function into the Farquhar, von Caemmerer, and Berry C₃ photosynthesis model. The model output showed that RuBP-limited photosynthesis is most affected by the φ_PSII temperature response as leaf temperatures increase or decrease further from the optimum temperature of φ_PSII. In addition to providing a new φ_PSII temperature response function, we also highlight key unanswered questions surrounding the φ_PSII temperature response that, if addressed, could bolster efforts to predict the effects of temperature on photosynthesis.