A multiple chamber, semicontinuous, crop carbon dioxide exchange system: Design, calibration, and data interpretation

Long-term, whole crop CO2 exchange measurements can be used to study factor s affecting crop growth. These factors include daily carbon gain, cumulativ e carbon gain, and carbon use efficiency, which cannot be determined from s hort-term measurements. We describe a system that measures semicontinuously crop CO2 exchange in 10 chambers over a period of weeks or months. Exchang e of CO2 in every chamber can be measured at 5 min intervals. The system wa s designed to be placed inside a growth chamber, with additional environmen tal control provided by the individual gas exchange chambers. The system wa s calibrated by generating CO2 from NaHCO3 inside the chambers, which indic ated that accuracy of the measurements was good (102% and 98% recovery for two separate photosynthesis systems), Since the systems measure net photosy nthesis (P-net, positive) and dark respiration (R-dark, negative), the data can be used to estimate gross photosynthesis, daily carbon gain, cumulativ e carbon gain, and carbon use efficiency. Continuous whole-crop measurement s are a valuable tool that complements leaf photosynthesis measurements. Mu ltiple chambers allow for replication and comparison among several environm ental or cultural treatments that may affect crop growth. Example data from a 2 week study with petunia (Petunia xhybrida Hort, Vilm.-Andr.) are prese nted to illustrate some of the capabilities of this system.