TRANSPIRATION RESPONDING TO LIGHT CONDITIONS IN CONTROLLED ENVIRONMENTS-EFFECT OF INFRARED RADIATION

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Transpiration rate (E), leaf conductance (C_L), leaf temperature (T_L) and vapor density difference (W_L-W_A) between leaf and air in cucumber plants were examined in a phytotron glass room and a growth chamber under different light conditions. In the phytotron, intensity of solar radiation was variable according to solar altitude and sky conditions, and E, T_L and W_L-W_A in the daytime varied with the intensities of the solar radiation: The respective elevations of E, T_L and W_L-W_A were remarkably higher on a fair day as compared with those on a rainy day. On the other hand, C_L in the daytime was kept almost constant even in variable intensities of solar radiation, and E in the daytime was linearly related to W_L-W_A which was responsible for evaporative demand against the plant. The same effects of the light condition on E, C_L, T_L and W_L-W_A were found in the growth chamber under two different artificial lights (metal halide lamps with heat absorbing filter and without the filter) which were set at equal PPFD but contained different intensities of infrared radiation. These results indicate that infrared radiation affects transpiration mainly through the physical process in vapor diffusion from leaf to air. Thus, the infrared radiation were responsible for the increase in evaporative demand against the plant by raising W_L-W_A which varied with T_L affected directly by the radiation.
九州大学の論文