Normal cyclic variation in CO2 concentration in indoor chambers decreases leaf gas exchange and plant growth

Authors: BUNCE, JAMES - Retired ARS Employee

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2020
Publication Date: 5/23/2020
Citation: Bunce, J.A. 2020. Normal cyclic variation in CO2 concentration in indoor chambers decreases leaf gas exchange and plant growth. Plants. 9(5):663. https://doi.org/10.3390/plants9050663.
DOI: https://doi.org/10.3390/plants9050663

Interpretive Summary: Because atmospheric CO2 concentrations are expected to continue to rise, attempts to identify crop lines with larger yield stimulation at projected elevated atmospheric CO2 concentrations are becoming more common. However, there is new concern that systems often used to produce elevated CO2 in field experiments may have incorrect results because of the large variation in CO2 concentrations those systems produce. This experiment tested whether the amount of variation in CO2 concentration occurring in indoor chambers and glass houses is also large enough to alter crop growth. The results indicate that indoor experiments as currently conducted may have the same problem as field experiments. These results will be of interest to scientists attempting to identify crop lines better adapted to projected future atmospheric conditions.

Technical Abstract: Attempts to identify crop genetic material with larger growth stimulation at projected elevated atmospheric CO2 concentrations are becoming more common both in indoor and field experiments. The probability of reductions in photosynthesis and yield caused by short-term variation in CO2 concentration within elevated CO2 treatments in the free-air CO2 enrichment plots raises the question of whether similar effects occur in glasshouse or indoor chamber experiments. These experiments were designed to test whether even the normal, modest, cyclic variation in CO2 concentration typical of indoor and glasshouse exposure systems have persistent impacts on photosynthesis and growth, and to explore mechanisms underlying the responses observed. Wheat, cotton, soybeans and rice were grown from seed in indoor chambers at a mean CO2 concentration of 560'ppm, with cyclic variation with standard deviations of either 4.5 or 18.0 ppm. Photosynthesis, stomatal conductance and biomass were reduced in all four species by the larger variation in CO2 concentration. Tests of differential rates of stomatal opening and closing with step changes in CO2, and tests of responses to cycling of CO2 were also conducted on individual leaves of these and other species, using a leaf gas exchange system. Reduced stomatal conductance due to larger amplitude cycling of CO2 in indoor chambers occurred even in species such as soybeans and rice which had equal rates of opening and closing in response to step changes in CO2. The gas exchange results further indicated that reduced mean stomatal conductance was not the only cause of reduced photosynthesis in variable CO2 conditions.