Resistance to Water Transport in Rice Plants1

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Abstract
Rice (Oryza sativa L.) is grown either in continuously flooded “lowland” soils or under rainfed conditions in “upland” soils. The objective of the study was to determine whether there are differences in resistance to water transport between plants grown in flooded and non‐flooded soils. This information may be useful in understanding the plant‐water relations under two cultural practices.In a greenhouse, rice variety ‘IR‐8’ was grown under flooded and 0.33 bar soil suction for 45 to 50 days. The resistance to water transport in different plant parts and in the whole plant was measured by a transient flow method. The effect of an increased air saturation deficit from 15 mb to 45 mb on transpiration rate and on leaf water potential was studied in a controlled environment chamber.The resistance to water transport in the non‐flooded plants was nearly twice as high as in the flooded plants. The non‐aerenchymatous roots of non‐flooded plants had about 17 times more resistance than aerenchymatous roots of flooded plants.The gradient between leaf and soil water potential increased markedly when plants were exposed to high air saturation deficit; however, the transpiration rate remained almost constant.These studies indicate the existence and development of large resistances to water transport in rice plants.

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