Photosynthetic Efficiencies of Rice under Humid and Dry Conditions, as Affected by Varietal Difference in Leaf Areal Nitrogen Content

Abstract

Four rice varieties, Bluebelle, IR8, Panbira and Sensho, were grown on flooded and dry soil in pots in a glasshouse. Photosynthetic rate (P, C02 uptake/time), transpiration rate (Tr, H20 release/time) and temperature (T) of the second expanded leaf (whole single leaf blade) from the top of the main stem were measured under controlled aeration (40 minutes wet, then 40 minutes dry) and illumination in an air sealed leaf chamber in the laboratory, together with leaf area (LA), fresh weight (FW), dry weight (DM) and nitrogen content (LN). CO2 diffusive resistance in the gaseous phase was estimated from Tr. T and air humidity, and actual leaf water content after P and Tr measure-ments was estimated from FW and DM. Photosynthetic efficiencies were evaluated on two bases : per unit leaf area (P/LA) and per unit leaf nitrogen (P/LN). Four varieties tested showed a marked difference in their leaf density-thickness as indicated by leaf areal nitrogen content (LN/LA). Judging Lrom the leaf nitrogen efficiency in photosynthetic energy conversion (P/LN), it was concluded that thinly expanded leaves with a highwer LN/LA were adapted to humid and densely thick leaves with a higher LN/LA were adapted to dry condltlons. With regard to this concluslon relatlonshlps between leaf density-thickness, dehydration avoidance ability, and C02 diffusive resistance were also discussed.