Photosynthesis and Stomatal Conductance with CO2‐Enrichment of Containerand Field‐Grown Soybeans1

Abstract

AbstractThe present experiment was an attempt to study the differences between photosynthetic responses of pot‐grown and field‐grown soybean [Glycine max(L.) Merr., ‘Bragg’] plants to atmospheric CO2enrichment at six levels of irradiance and four leaf temperatures. Plants were grown in field soil or in pots containing an artificial substrate at five elevated atmospheric CO2levels and two water regimes in open top field chambers. Under well‐watered conditions plants grown in the pots had lower stomatal conductances and lower rates of net photosynthesis than plants grown in the field. However, the field‐grown plants responded to a less extent to increasing atmospheric CO2concentration than pot‐grown plants. The photosynthesis‐ irrdiance relationships were linear in the field‐grown plants and curvilinear in the pot‐grown plants. At the highest irradiance level tested (1400 µmol m−2s−1), the field‐grown plants had maximum net photosynthetic rates of 43 and 48 mg CO2dm−2h−1at 332 and 623 µL L−1CO2respectively. The pot‐grown plants were irradiance saturated at a level of 700 µmol m−2s−1and net leaf photosynthetic rates were 18 and 28 mg CO2dm−2h−1at 332 and 623 µL L−1CO2, respectively. Water stress caused a reduction in both stomatal conductance and net photosynthetic rate in the leaves of pot‐grown plants. The effect of leaf temperature on net photosynthethis and stomatal conductance depended upon the atmospheric CO2concentration and rooting media. High temperature increased net photosynthetic response to CO2enrichment at high CO2concentrations but not at low CO2concentrations.