Difference in diurnal courses of microclimate and gas exchange on rice (Oryza sativa L.) leaves with various orientations in a paddy field

Seiichi Nishimura, Kazuyuki Itoh, Yanhong Tang and Hiroshi Koizumi(2000) : Difference in diurnal courses of microclimate and gas exchange on rice (Oryza sativa L. ) leaves with various orientations in a paddy field. Journal of the Japanese Agricultural Systems Society, Vol.16, No.2, 156 - 162. Diurnal courses of photosynthesis and transpiration were measured on rice leaves within the same height range and with four different azimuth angles (leaf orientation ; east, south, west, north) by the closed chamber method in the field. Diurnal courses of photon flux density (PFD) on leaf surfaces were quite different among the four leaf orientations. Accordingly, diurnal courses of leaf photosynthesis also differed with the leaf orientation. However, in most cases, significant difference in the relationship of PFD on leaf surface and the leaf photosynthesis (light-photosynthesis curve) was not found among the four leaf orientation. Stomatal conductance gradually decreased from the morning to the evening, and did not show any appreciable difference among the four leaf orientations either. Daily total PFD on the surfaces of east-, west- and north-oriented leaves were about 37%, 28% and 80% lower than that on the south-oriented leaf, respectively. An estimation showed that daily carbon gains on east-, west- and north-oriented leaves were about 20%, 3% and 36% lower than that on the south-oriented leaf, respectively. On the contrary, daily water consumptions by transpiration of east-, west- and north-oriented leaves were similar to that of south-oriented leaf (ranged between 0.9 and 1.1 times). The present study therefore suggests that, the diurnal course of leaf photosynthesis is mainly subjected to the microclimatic PFD value (PFD on leaf surface) and its diurnal course, and is changeable with leaf's orientation and inclination, which affects the amount of daily leaf assimilation, whereas stomatal aperture and water consumption are comparatively uniform and not largely affected by the leaf orientation in the canopy.