Growth and Specific Nodule Activity of Soybean during Application and Recovery of a Leaf Moisture Stress

Abstract

Soybean plants growing a day/night temperatures of 30/18.degree., 26/18.degree. and 22/18.degree. C were subjected to a single drying and recovery cycle during an 18-19 day period in the early to midpod development stage. Leaf total electrochemical water potential was reduced to about -24 bars during the 4 day drying cycle at all temperatures, but recovered to control levels upon rewatering. The changes in dry matter accumulation in whole plants and plant parts, specific activity of nodules as measured by acetylene reduction, and levels of adenosine phosphates in nodules were measured periodically during stress and recovery. Vegetative and reproductive growth were about equally suppressed by the leaf moisture stress. Both rate of appearance and number of pods were reduced. However, a similar average weight per pod for both stress and control plants at the conclusion of the recovery period suggests that individual pod development is not irreversibly affected by a single stress cycle and that yield potential is restricted by a decrease in number of pods or seed. Dry matter accumulation in plants and pods was unaffected by temperature. Specific nodule activity and energy charge of nodules declined concurrently with leaf moisture potential. Recovery of specific nodule activity following rewatering lagged behind recovery of leaf moisture potential, but energy charge of nodules recovered as rapidly as leaf moisture potential upon rewatering. Thus, the delayed recovery of specific nodule activity does not appear to be related to recovery of energy charge of the nodules.