Super-Optimal CO2 Reduces Seed Yield But Not Vegetative Growth in Wheat
- Timothy P. Grotenhuis and
- Bruce Bugbee
Although terrestrial atmospheric CO2 levels will not reach 1000 μmol 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 10 000 μmol mol−1 (1%). Numerous studies have examined CO2 effects up to 1000 μmol mol−1, but biochemical measurementisn dicate that the beneficial effects of CO2 can continue beyond this concentration. We studied the effects of near-optimal (≈1200 μmol mol−1) and super-optimal CO2 levels (2400 μmol 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 μmol 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 μmol mol−1 reduced seed yield by 22% (P < 0.001) in cv. Veery-10 and by 15% (P < 0.001) in cv. USU-ApogeeS. uper-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 fromh alf to full sunlight. Subsequenttr ials revealed that super-optimal CO2 during the interval between 2 wk before and after anthesis mimickedth e effect of constant super-optimal O2. 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 uggest that super-optimal CO2 inhibits some process that occurs near the time of seed set resulting in decreased seed set, seed mass, and yield.
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