A Method For Opening Stomata And Measuring Photosynthetic Capacity v1

Stomatal closure can bottleneck photosynthetic measurements, making it difficult or impossible to characterize the throughput of the underlying biochemical machinery. This protocol uses a low-CO2 conditioning period to encourage stomatal opening, followed by ramping up CO2 levels across nine light levels. Unlike classical methods that characterize A/Ci curves at fixed, saturating light and measure A/Q curves separately, this approach measures A/Ci curves across light levels, producing a rich 3D surface capturing the interactions between CO2, light, and carbon assimilation. The protocol is encoded in an automated LI-6800 background program, which additionally includes dark-adapted fluorescence measurements and intermittent active MultiPhase fluorescence flashes. The program's default configuration takes approximately three hours to run after external leaf dark adaptation and instrument warmup.