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Water Potential and Component Potentials in Expanded and Unexpanded Leaves of Two Xeric Grasses

1978; Wiley; Volume: 44; Issue: 4 Linguagem: Inglês

10.1111/j.1399-3054.1978.tb01642.x

1399-3054

James O. MAXWELL, R. E. Redmann,

Soil and Unsaturated Flow

Abstract Water (ψ), osmotic (ψ s +ψ m ) and pressure (ψ p ) potentials were measured in three leaf regions of Agropyron dasystachyum and A. smithii grown in the field. Spanner‐type thermocouple psychrometers were used to measure ψ and (ψ m +ψ m ). Absolute water content (AWC) was measured gravimetrically. The ψ and ψ p were slightly lower in the emerging leaf blade (EBI) than in the last fully emerged leaf blade (FEBI); (ψ s +ψ m ) and AWC were similar in the two regions. A gradient as large as 0.7 MPa was observed between the EBI and the base of the same emerging leaf (EBs); the latter included the meristematic regions. Although (ψ s +ψ m ) and ψ p were generally higher in the EBs, the gradients diminished as the level of stress increased in the shoot. Under moderate water stress the ψ p of the EBs remained constant relative to the ψ p in the exposed blades. The large ψ gradient within the growing leaf could have resulted from high resistance imposed by poor vascular development in the intercalary meristem. Ability to maintain a relatively large ψ gradient may be of general significance in buffering the growing region of xeric grass leaves from extreme, short‐term fluctuations in water stress that occur in exposed leaf blades.