|RUIZ-VERA, URSULA - University Of Illinois|
|SIEBERS, MATHEW - University Of Illinois|
|DRAG, DAVIE - University Of Illinois|
Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2015
Publication Date: 7/5/2015
Citation: Ruiz-Vera, U.M., Siebers, M.H., Drag, D.W., Ort, D.R., Bernacchi, C.J. 2015. Canopy warming caused photosynthetic acclimation and reduced seed yield in maize grown at ambient and elevated [CO2]. Global Change Biology. 21:4237-4249.
Interpretive Summary: Increases in atmospheric carbon dioxide and resulting global warming both have direct impacts on ecosystem functioning. This study addresses the response of maize, a dominant crop grown worldwide, to both increases in CO2 and temperature while growing under typical agronomic conditions. The results confirm previous results that rising CO2 has little impact on maize growth or photosynthesis, show rising temperatures decrease photosynthesis, biomass, and yields. Decrease in harvested yield is driven by fewer kernels developing per cob, which can be a direct consequence of photosynthetic acclimation to higher temperatures, but may be driven by high temperature effects on reproductive development.
Technical Abstract: Rising atmospheric CO2 concentration ([CO2]) and attendant increases in growing season temperature are expected be the most important global change factors impacting production agriculture. Although maize is the most highly produced crop worldwide, few studies have evaluated the interactive effects of elevated [CO2] and temperature on its photosynthetic physiology, agronomic traits or biomass and seed yield under open field conditions. This study investigates the effects of rising [CO2] and warmer temperature, independently and in combination, on maize grown in the field throughout a full growing season. Free Air CO2 Enrichment (FACE) technology was used to target atmospheric [CO2] to 200 µmol mol-1 above ambient [CO2] and infrared heaters to target a plant canopy increase of 3.5°C, with actual season-mean heating of ~2.7°C, mimicking conditions predicted by the second half of this century. Photosynthetic gas exchange parameters, leaf nitrogen and carbon content, leaf water potential components, and developmental measurements were collected throughout the season and biomass and yield were measured at the end of the growing season. As predicted for a C4 plant, elevated [CO2] did not stimulate photosynthesis, biomass or yield. Canopy warming caused a large shift in above ground allocation by stimulating season long vegetative biomass and decreasing reproductive biomass accumulation at both CO2 concentrations, resulting in decreased harvest index. Warming caused a reduction in photosynthesis due to down-regulation of photosynthetic biochemical parameters and the decrease in the electron transport rate. The reduction in seed yield with warming was driven by reduced photosynthetic capacity and by a shift in above-ground carbon allocation away from reproduction. This field study portends that future warming will reduce yield in maize and this will not be mitigated by higher atmospheric [CO2] unless appropriate adaptation traits can be introduced into future cultivars.