Rapid Chlorophyll a Fluorescence Light Response Curves Mechanistically Inform Photosynthesis Modeling1[OPEN]

Crop improvement is crucial to ensuring global food security under climate change, and hence there is a pressing need for phenotypic observations that are both high throughput and improve mechanistic understanding of plant responses to environmental cues and limitations. In this study, chlorophyllafluorescence light response curves and gas-exchange observations are combined to test the photosynthetic response to moderate drought in four genotypes ofBrassica rapa. The quantum yield of PSII (phi(PSII)) is here analyzed as an exponential decline under changing light intensity and soil moisture. Both the maximum phi(PSII)and the rate of phi(PSII)decline across a large range of light intensities (0-1,000 mu mol photons m(-2)s(-1);beta(PSII)) are negatively affected by drought. We introduce an alternative photosynthesis model (beta(PSII)model) incorporating parameters from rapid fluorescence response curves. Specifically, the model uses beta(PSII)as an input for estimating the photosynthetic electron transport rate, which agrees well with two existing photosynthesis models (Farquhar-von Caemmerer-Berry and Yin). The beta(PSII)model represents a major improvement in photosynthesis modeling through the integration of high-throughput fluorescence phenotyping data, resulting in gained parameters of high mechanistic value. Chlorophyll a fluorescence rapid light response curves improve mechanistic models of drought limitations to photosynthetic electron transport.