The effect of gravity on surface temperature and net photosynthetic rate of plant leaves

To clarify the effects of gravity on heat/gas exchange between plant leaves and the ambient air, the leaf temperatures and net photosynthetic rates of plant leaves were evaluated at 0.01, 1.0, 1.5 and 2.0 G of 20 seconds each during a parabolic airplane flight. Thermal images of leaves were captured using infrared thermography at an air temperature of 26 °C, a relative humidity of 15 % and an irradiance of 260 W m ^-2 . The net photosynthetic rates were determined by using a chamber method with an infrared gas analyzer at an air temperature of 20 °C, a relative humidity of 50 % and a photosynthetic photon flux of 0.5 mmol m ^-2 s ^-1 . The mean leaf temperature increased by 1 °C and the net photosynthetic rate decreased by 13 % with decreasing gravity levels from 1.0 to 0.01 G. The leaf temperature decreased by 0.5 °C and the net photosynthetic rate increased by 7 % with increasing gravity levels from 1.0 to 2.0 G. Heat/gas exchanges between leaves and the ambient air were more retarded at lower gravity levels. A restricted free air convection under microgravity conditions in space would limit plant growth by retarding heat and gas exchanges between leaves and the ambient air.