Abstract
The effects of atmospheric humidity on vegetative growth of paddy and upland rice were compared. A low atmospheric humidity (60%RH) significantly decreased the dry-matter production in paddy rice but not in upland rice. In paddy rice, exposure to low atmospheric humidity significantly increased the stomatal density in leaves, stomatal aperture and the ratio of stomatal apparatus to leaf area. Thus, stomatal opening was only slightly decreased by the low humidity, resulting in a striking increase in transpiration rate per unit leaf area and marked reduction in water potential of leaf blade. On the other hand, in upland rice, stomatal density and stomatal apparatus area were not influenced by exposure to a low humidity and the ratio of stomatal apparatus area to leaf area was not influenced by atmospheric humidity up to 60%RH. In paddy rice, the relative leaf expansion rate was significantly reduced by exposure to a low humidity, but in upland rice, it was not. Thus, in the present study the low atmospheric humidity reduced the leaf expansion rate without reducing the net assimilation rate in paddy rice, but not in upland rice. This may be why the effect of atmospheric humidity on growth and dry-matter production differed between paddy and upland rice.
