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A Field Study on Leaf Water Potential, Transpiration and Plant Resistance to Water Flow In Rice¹

Plant water deficits develop in rice (Oryza sativa L.) cultivars even under submerged soil conditions. Measurements of leaf water potential, transpiration rate, stomatal resistance, and leaf and air temperature were made on four rice cultivars, ‘M1-48,’ ‘Dular,’ ‘IR36,’ and ‘IR20,’ grown in a wetland irrigated field during the dry season. The response of leaf water status to transpiration rate and the magnitude of plant resistance to liquid-phase water flow were evaluated. Hourly observations on 2 clear days, 41 days after transplanting, revealed that during peak periods of transpiration, leaf water potentials declined to –10 to –17 bars and differed among cultivars. Ml-48, a dryland local cultivar, maintained a higher leaf water potential than high yielding wetland cultivars. Using the Ohm's law analogue resistances to water flow in plants were estimated. A curvilinear relationship between plant resistance and transpiration rate was observed. Hysteresis was observed in the leaf water potential: transpiration rate relationship. The trend in hysteresis of the two cultivars IR20 and M1-48, demonstrated differential behavior to water flow. Wetland rice culture allows study of the nature and cause of plant resistance to water flow and their direct interpretation because of minimal soil resistance to water flow and a constant (near zero) soil water potential.

Key Words: Oryza sativa L. • Liquid phase plant resistance • Water transport resistance

² Collaborative research fellow (Present address: Dep. of Soil Science, G. G. Pant Univ. of Agriculture and Technology, Pantnagar Dist. Nainital, U.P., India) and agronomist.

Received for publication October 29, 1979.