APPLICATION OF MONITORING FRESH WEIGHT TO ANALIZING GROWTH RESPONSES TO AIR TEMPERATURE AND LIGHT INTENSITY IN LEAF LETTUCE

The top fresh weight was monitored with a device composed of hydroponic and load cells. The air temperature was stepwisely changed every 12 hours under continuous light of several intensities at vapor pressure deficit(VPD) of 0.4 kPa. Growth rates of the top fresh weight were optimum at air temperatures of 25 or 30 °C, and saturated at photon fluxdensity(400˜700 nm) of 320 or 410 μ mol m^-2 s^-1.

Photosynthetic rates at 0.4 kPa of VPD were optimum at 25 or 30 °C under several light intensities, and saturated at 1300 μ mol m^-2 s^-1. The saturation point was higher than that of the growth rate of the top fresh weight.

The top fresh weight was monitored in darkness (12 hours) following a light period(9 hours) at several light intensities. The top fresh weight increased drastically within the first hour in the dark, depending on the previous light intensity. The increment of the top fresh weight in the 12 h darkness likely correlated to the previous photosynthtic rate. Respiration decreased after the 12 h darkness, while the fresh weight in the dark continued to increase for 5 days.

It was suggested that monitoring fresh weight can be applied to the analysis of growth responses to environment.

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