Combined gas exchange, fluorescence, and electrochromic shift measurements
A LI-COR 6800-12A clear-top chamber (LI-COR Inc., Lincoln, NE, USA) was modified to incorporate an optical bench for making measurements. The bottom plate of the clear top chamber was removed and replaced with a 3D-printed backplate with an infrared and an optical detector. These detectors were connected to an Idea Spec (Hall et al. 2013). A front plate was also 3D printed to secure a scattering optic to the top of the 6800-12A. Behind the scattering optic was an array of LEDs containing eight actinic blue and red LEDs, capable of producing up to 2,500 µmol m-2 s-1 constantly or a saturating flash up to 15,000 µmol m-2s-1, at an approximately 90% red/10% blue ratio. Measuring LEDs for electrochromic shift (ECS) were 520 nm, with 505 nm and 535 nm as correction wavelengths for zeaxanthin andqE effects on the 520 nm signal. Measuring lights for PSI measurements were at 820 nm with 910 nm as a correction wavelength. Measurements of chlorophyll fluorescence used the 520 nm LEDs as an excitation light. Measurements of PSI were performed according to Kanazawa et al. (2017) and measurements of ECS were performed according to Takizawa et al . (2007). These modifications to the chamber allowed high precision optical measurements simultaneous with high precision gas exchange measurements, especiallyA and intercellular CO2 partial pressure (Ci ) allowing construction ofA /Ci curves.