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Response of Oats to Water Deficit. I. Physiological Characteristics¹

Although an insufficient supply of water is commonly associated with reduced crop yields, the manner in which water deficits affect the functioning of many common field crops is not well established. The purpose of this study was to quantify the effects of a water deficit on some physiological processes of spring oats (Avena sativa L. ‘Jaycee’). The plants were subjected to water deficits under a field environment far 9 to 11 days at the boot stage, at anthesis through early grain formation stage, and at both stages in combination. Relative leaf water content (RLWC) as determined by the relative turgidity method was used as a measure of water deficit. Leaf diffusion resistance (LDR) was monitored using a diffusion porometer. The net photosynthetic rate (NPR) of the oat plants was determined using an infrared gas analyzer. Severe water stress at all stages of development studied caused about an 80% decline in NPR. LDR increased with a decrease in RLWC. Stress during boot stage reduced the photosynthetic sensivity of the plants to subsequent stress at the anthesis through early grain formation stage. On rewatering, LDR and RLWC recovered completely within 1 to 6 days; however, the net photosynthetic rate of plants stressed at the anthesis through grain formation stage showed a more gradual and incomplete recovery than plants stressed at other stages. The plants stressed during boot stage alone, but adequately watered thereafter, exhibited significantly higher NPR than the control plants. The results indicate that leaf diffusion resistance and net photosynthetic rate of oats show acute sensitivity to plant water deficits. Hence, these parameters hold promise as aids in determining permissible water deficit limits and in irrigation scheduling.

Key Words: Photosynthesis • Leaf diffusion Resistance • Relative leaf water content • Boot stage • Grain formation stage

² Former research assistant and professor, respectively, Plant Science Dep. and the South Dakota Water Resources Institute, South Dakota State Univ., Brookings, SD 57006. The senior author is now soil physicist in the Dep. of Soils, Punjab Agricultural Univ., Ludhiana, India.

Received for publication May 15, 1975.