title: Super-optimal CO2 reduces seed yield but not vegetative growth in wheat.
abstract: Although terrestrial atmospheric CO2 levels will not reach 1000 micromoles mol-1 (0.1%) for decades, CO2 levels in growth chambers and greenhouses routinely exceed that concentration. CO2 levels in life support systems in space can exceed 10000 micromoles mol-1(1%). Numerous studies have examined CO2 effects up to 1000 micromoles mol-1, but biochemical measurements indicate that the beneficial effects of CO2 can continue beyond this concentration. We studied the effects of near-optimal (approximately 1200 micromoles mol-1) and super-optimal CO2 levels (2400 micromoles mol-1) on yield of two cultivars of hydroponically grown wheat (Triticum aestivum L.) in 12 trials in growth chambers. Increasing CO2 from sub-optimal to near-optimal (350-1200 micromoles mol-1) increased vegetative growth by 25% and seed yield by 15% in both cultivars. Yield increases were primarily the result of an increased number of heads per square meter. Further elevation of CO2 to 2500 micromoles mol-1 reduced seed yield by 22% (P < 0.001) in cv. Veery-10 and by 15% (P < 0.001) in cv. USU-Apogee. Super-optimal CO2 did not decrease the number of heads per square meter, but reduced seeds per head by 10% and mass per seed by 11%. The toxic effect of CO2 was similar over a range of light levels from half to full sunlight. Subsequent trials revealed that super-optimal CO2 during the interval between 2 wk before and after anthesis mimicked the effect of constant super-optimal CO2. Furthermore, near-optimal CO2 during the same interval mimicked the effect of constant near-optimal CO2. Nutrient concentration of leaves and heads was not affected by CO2. These results suggest that super-optimal CO2 inhibits some process that occurs near the time of seed set resulting in decreased seed set, seed mass, and yield.
authors.affiliation: Crop Physiology Lab, Dep. of Plants, Soils, and Bimeteorology, Utah State Univ., Logan 84322-4820, USA.
authors.forename: T P
authors.initials: TP
authors.lastname: Grotenhuis
authors.forename: B
authors.initials: B
authors.lastname: Bugbee
mesh_terms: D018533:Biomass; D002245:Carbon Dioxide / Q000494:pharmacology* / Q000633:toxicity; D004305:Dose-Response Relationship, Drug; D004780:Environment, Controlled; D005030:Ethylenes / Q000378:metabolism; D008027:Light; D017785:Photons; D010788:Photosynthesis; D010937:Plant Growth Regulators / Q000378:metabolism; D012639:Seeds / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D014908:Triticum / Q000187:drug effects* / Q000254:growth & development* / Q000378:metabolism
chemical_list: D005030:Ethylenes; D010937:Plant Growth Regulators; D002245:Carbon Dioxide; C036216:ethylene