Leaf Elongation and Turgor Pressure in Field‐grown Soybean1

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Abstract
Cell and leaf elongation have been reported to be highly sensitive to plant water deficit and may represent the primary mechanism of stress and yield reduction. This study was designed to determine if leaf expansion is restricted by the routine daytime water deficit experienced by field plants in moist soil. Leaf elongation in soybean [Glycine max (L.) Merrill ‘Rampage’] was monitored during several 2 to 4‐day periods in the field in conjunction with pressure bomb measurement of water and osmotic and turgor potential. Short‐term (minutes) leaf‐elongation rate was highly responsive to step changes in water deficit but gradually recovered over periods of about an hour. Length that was lost during the transient rate reduction tended to be made up by high rates following improved water status. Mean elongation rates were not limited by normal daytime water deficit (turgor pressure as low as 2 bars), except late in the season when pod‐filling occurred at nodes adjacent to the growing leaves. Elongation rate was always sensitive to temperature. We conclude that within the range of moderate, daytime water deficits we encountered, soybean leaves may adapt to the extent that turgor pressure does not limit growth.