Leaf wall yield threshold of field‐grown soybean measured by vapour pressure psychrometry

Abstract

Abstract. Wall‐yield threshold pressures of growing leaves obtained from field‐grown soybean (Glycine max [L.] Merr.) plants were measured in vapour pressure psychrometers. The plants were grown either under well‐watered or water deficit conditions. Wall‐yield threshold pressures were measured at night when turgor pressure was expected to exceed the wall‐yield threshold pressure both in drought‐stressed and well‐watered growing leaves. Wall‐yield threshold pressure increased as the area of the growing leaves increased in both treatments. After an 8‐d drought, wall‐yield threshold pressure in leaves which had recently emerged from the meristem was 0.50 MPa, while in well‐watered leaves these values ranged from 0.03 to 0.23 MPa. Upon release from drought, wall‐yield threshold pressure rapidly returned to unstressed values.