Influence of Rate of Development of Leaf Water Deficits upon Photosynthesis, Leaf Conductance, Water Use Efficiency, and Osmotic Potential in Sorghum

Authors

  • M. M. JONES,

    1. Department of Environmental Biology, Research School of Biological Sciences, Australian National University, P.O. Box 475, Canberra City, A.C.T., Australia 2601 and Division of Plant Industry, CSIRO, P.O. Box 1600, Canberra City, A.C.T., Australia 2601
    Search for more papers by this author
  • H. M. RAWSON

    1. Department of Environmental Biology, Research School of Biological Sciences, Australian National University, P.O. Box 475, Canberra City, A.C.T., Australia 2601 and Division of Plant Industry, CSIRO, P.O. Box 1600, Canberra City, A.C.T., Australia 2601
    Search for more papers by this author

Abstract

This study reports the effect of rate of development of leaf water deficits in soil-grown sorghum (Sorghum bicolor) on the relationship of net photosynthesis, leaf conductance, and water use efficiency to leaf water potential, and on the degree of solute accumulation (osmotic adjustment). Recovery of these processes on rewatering, and responses during a second stress cycle were also studied. The most rapid rate of stress (1.2 MPa day−1) resulted in no solute accumulation and the lowest rate of net photosynthesis and leaf conductance for any given leaf water potential during stress. Stress at 0.7 and 0.15 MPa day−1 led to equal solute accumulations of approximately 0.6 MPa, but net photosynthesis, leaf conductance, and water use efficiency at a given leaf water potential were lower with the faster rate of stress (0.7 MPa day−1). Additionally, leaf conductance at a given leaf turgor potential was lowest at the 1.2 MPa day−1 stress rate, slightly higher at the intermediate rate of stress, and clearly highest at the slowest rate of stress. Recovery of both net photosynthesis and leaf conductance upon rewatering was rapid, taking less than 3 days, but full recovery of osmotic potential took between 6 and 11 days. One slow stress cycle had no influence on relationships during a second cycle. The concept of a threshold leaf water potential for stomatal closure is discussed and the conclusion reached that stomatal closure occurs slowly over a wide range of leaf water potential (> 1.0 MPa), the range being greater for slower rates of stress.

Ancillary