Water Relations and Physiological Activity of Potatoes1

Abstract

The effects of water stress on internal water potential components and specific physiological processes were investigated in field grown potatoes ( Solanum tuberosum L. cv. Viking). Leaf water potential ( ψ leaf ) as estimated by the pressure chamber, was not directly related to soil water potential ( ψ soil ) until a specific minimum ψ soil was attained. Subsequently ψ leaf did not increase in response to increases in ψ soil . Water stress affected physiological processes such as stomatal resistance, photosynthesis and enzyme activity. A decline in ψ leaf was apparently responsible for increased stomatal resistance and decreases in photosynthetic rates. The activities of ribulose diphosphate carboxylase and phosphoenolpyruvate carboxylase decreased as ψ leaf declined. The relationship between water stress and physiological processes and the inability of ψ leaf to respond to increases in ψ soil after a maximum stress may partially explain the extreme sensitivity of potatoes to even mild water stress.