Response of source–sink relationship in soybean to temperature

Abstract

The need for carefully defined conditions to demonstrate sink-source interaction was investigated using 'Biloxi' soybean grown under defined growth conditions. When the source area was reduced in seedlings by removal of the cotyledons and one primary leaf, the CO2 uptake in the remaining leaf was increased at 24 °C but not at 27 °C. The 17% increase in the rate of CO2 uptake at 24 °C was accompanied by an increase of assimilate export of about 5% over 24 h. The effects on CO2 uptake at 21 and 30 °C were smaller than at 24 °C but larger than at 27 °C. The percentage of assimilated 14C that was translocated was also increased at 27 °C, but there was no accompanying stimulation of CO2 uptake. Fruiting plants at 24 °C had close to double the CO2 uptake rates of barren plants; whereas at 27 °C the rates were the same. Removing the pods reduced the CO2 uptake at 24 °C to close to that of barren plants. Sink activity appeared to limit CO2 uptake over a very narrow temperature range below optimum temperatures for growth, whereas at optimum temperatures CO2 uptake appeared to limit growth.