Measurement of Gas Exchange Characteristics of Developing Wheat in the Biomass Production System

The PESTO (Photosynthesis Experiment and System Testing and Operation) spaceflight experiment is designed to directly measure gas exchange of developing stands of wheat (Triticum aestivum L.) on the International Space Station (ISS). Gas exchange measurements will characterize photosynthesis and transpiration in microgravity at different stages of development. The Biomass Production System (BPS), a double middeck-sized plant growth will be the plant growth hardware used to support this experiment on-board ISS. This report presents results from a 10-day functional test of PESTO protocols in the BPS.

Wheat canopy CO₂ assimilation rate for 14-24 day-old plants grown in the BPS chambers was 6-7 μmol m^-2 s^-1 during this test. Plant responses to CO₂ and photosynthetic photon flux (PPF) response curves were obtained at different stages of development by altering CO₂ and light conditions. PPF response curves were linear (r²=0.99) over the range evaluated, and the estimated light compensation point was 103 μmol m^-2 s^-1. The CO₂ compensation point was between 95 and 125 μmol mol^-1. Transpiration rates of approximately 3.8 L m^-2 day^-1 were estimated for 20-day-old plants from water additions to the plant root zone.