Gen-ichi Hirai

Studies on the Effect of the Relative Humidity of the Atmosphere on the Growth and Physiology of Rice Plants : Effects of relative humidity during the light and dark periods on the growth

Summary The seedlings of rice (Oryza sativa cv. Nipponbare) at a plant age of 3 leaves, were cultured for 10 days in a 12-h light/12-h dark cycle, and exposed to 60% (low) or 90% (high) relative humidity during the light and dark period in all combinations. Low humidity in light and high humidity in darkness, significantly increased the rate of leaf emergence, plant height, leaf area, leaf blade length, the number of roots, total root length and dry matter production as compared with low humidity in both light and dark periods. These results suggested that the effects of high humidity during the dark period on the growth and dry matter production is not nullified by low humidity during the light period. High humidity during the light period was significantly more effective than that during the dark period for the growth expressed by these parameters. The effects of high humidity during the light and dark periods on the plant height, leaf sheath length and width of leaf blade were additive, but those on the leaf-emergence rate, number of roots, total root length, leaf area, leaf blade length and dry matter production were not additive.

Varietal Differences in the Morphophysiological Response to Atmospheric Humidity in Rice

Abstract High atmospheric humidity promotes vegetative growth and dry-matter production in japonica rice. In this study, the varietal differences in the response to atmospheric humidity were examined using three japonica varieties (Nipponbare, Kinmaze, Yamadanishiki), one indica variety IR24 and japonica × indica variety (Milyang 23). The indica and japonica × indica varieties are referred to as indica varieties hereafter. The growth of the japonica varieties was greatly promoted by high humidity (90%) and greatly reduced by low humidity (60%), but that of the indica varieties was less sensitive to humidity and the growth was hardly affected by low humidity. We compared the responses of the above varieties to low humidity (water stress) using the plants under high humidity as a control. Under low humidity, as compared to the indica varieties, the japonica varieties had a higher stomatal density, longer stornata and larger stomatal aperture, resulting in a lower water potential in leaf blades and lower water -use efficiency. Under high humidity, the japonica and indica varieties showed a similar transpiration rate (per unit area), stomatal aperture and water-use efficiency, but the japonica varieties had a higher water content than the indica varieties. This may be why the japonica varieties show greatly suppressed growth and dry matter production under low humidity. These differences between the japonica and indica varieties in morphophysiological characters under low humidity might cause the varietal differences in the plant growth and dry matter production in rice.