Abstract
Photosynthesis (Pn) and transpiration (Tr) of rakkyo, a plant which can be cultivated without irrigation in sandy soil, is measured under several kinds of meteorological conditions, i. e., air temperature, relative humidity (RH) and light intensity. Several leaves of rakkyo were inserted into a small plastic assimilation box in a growth cabinet. The air temperature and relative humidity of the assimilation box and the growth cabinet were controlled. Experimental conditions were as follows: (1) Light intensity was constantly adjusted to 22klx by artificial lamps. Air temperatures were increased from 15°C to 35°C in 5°C steps. (2) Light intensity was charged from zero to 45klx. Four combinations of two air temperatures and two relative humidities were controlled in an assimilation box. These four combinations of environmental conditions were 15°C 50% RH, 15°C 70% RH, 30°C 25% RH and 30°C 70% RH.
Photosynthesis and water use efficiency were high under conditions of low air temperature and high relative humidity, while transpiration showed the opposite tendency. In the case of 15°C 70% RH, 40klx, photosynthesis was 26mg CO2/dm2•h, transpiration was 0.6g H2O/dm2•h, and water use efficiency (Pn/Tr) was 38mg CO2/gH2O. At 30°C 25% RH, Pn was 19mg, Tr 2g and Pn/Tr 8mg/g, respectively.
