INTERACTION OF TEMPERATURE AND CO2 ENRICHMENT ON SOYBEAN: PHOTOSYNTHESIS AND SEED YIELD

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Abstract
Seed yield and photosynthetic responses of soybean (Glycine max L. Merr. ’Ransom’) were studied in growth chambers at day/night temperatures of 18/12, 22/16, and 26/20 °C and atmospheric CO2 concentrations of 350, 675 and 1000 μL L−1. No seeds were produced at 18/12 °C within any of the CO2 concentrations. Numbers of pods and seeds increased with increasing temperature and CO2 levels. Carbon dioxide enrichment increased seed yield of soybean grown at moderately cool temperatures. This increase was associated with an increase in net photosynthetic rate. Leaf photosynthesis in response to CO2 enrichment increased more at 22/16 °C than at 26/20 °C. Increases in temperature and CO2 levels enhanced total growth of plants but hastened senescence of leaves. The extended photosynthetic capacity at cool temperatures did not result in allocating more dry matter to developing pods. CO2 enrichment at 26/20 °C resulted in greater seed yield increases than CO2 enrichment at lower temperatures.Key words: Soybean yield, low temperature, CO2 × temperature