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Annals of Botany 67: 549-554, 1991
© 1991 Annals of Botany Company

RESEARCH-ARTICLE

Variations in Root Water Potentials: Influence of Environmental Factors for Two Succulent Species

PARK S. NOBEL and CAROL H. LEE

Department of Biology and Laboratory of Biomedical and Environmental Sciences, University of California Los Angeles, California 90024, USA

Accepted: 20 February 1991   

Average root water potential ({psi}root) was determined with a pressure chamber for excised roots of two succulent CAM species, Agave deserti Engelm. and Opuntiaficus-indica (L.) Miller, under various environmental conditions. The drop in water potential between small lateral roots at the distal and the proximal ends averaged only 0.02 MPa for 20-cm-long roots of A. deserti and 0.08 MPa for 30-cm-long roots of O.ficus-indica. Thus, {psi}root determined for these roots (e.g. —0.30 MPa for A. deserti and —027 MPa for O.ficus-indica at a {psi}root, of —0.05 MPa) was similar to the root water potential at the cut end, especially for A. deserti. As the soil dried until {psi}root became similar to {psi}root (approx. — 0.5 MPa), ){psi}root decreased about twofold, with little further change in {psi}root occurring as soil dried further (to approx. —30 MPa). Increases in soil temperature from 5 to 45°C caused {psi}root to increase by an average of 014 MPa. For both species, {psi}root was 009 MPa lower near the end of the night compared with the end of the daytime, consistent with a concomitant predicted decrease in {psi}shoot averaging 015 MPa; under a low photosynthetic photon flux density, diel changes in {psi}root were greatly reduced. Such responses of {psi}root to environmental factors were interpretable in terms of known properties of {psi}shoot and the root hydraulic conductivities for the two species.

Agave deserti, hydraulic conductivity, Opuntia ficus-indica, root system, root temperature, soil-plant-atmosphere continuum, soil water, solar irradiation, water potential


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