Báo cáo lâm nghiệp: Control of gas exchange: evidence for root-shoot communication on drying soil

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Báo cáo lâm nghiệp: "Control of gas exchange: evidence for root-shoot communication on drying soil"Control of gas exchange: evidencefor root-shoot communication on drying soilT. Gollan W.J. Davies 2 1 2 J. Zhang U. Schurr1 Lehrstuhl Pflanzen6kologie, POB 10 f2Universitit Bayreuth, 51, 8580 Bayreuth, F.R.G., and2 University of Lancaster, Department of Biological Sciences, Bailrigg,Lancaster LA I 4YQ, U. K.Decrease in leaf conductance (stomatal maintained until a critical soil water with drying soil is a common phe-closure) content was reached. With the introduc-nomenon and has been reported in tion of thermodynamics in plant water rela-myriads of publications. Stomatal closure tions and the development of morewith soil drying generally occurs in parallel sophisticated measurement techniques,with a deterioration of plant water status. leaf water potential became the controllingWith a decrease in relative water content, factor in most experimental hypotheses. Itleaf turgor and water potential in general was an obvious thought, because stoma-decline. Since both leaf conductance and tal movements operate via changes in tur-leaf water potential decrease more or less gor of the guard cells and the surroundingat the same time during a drying cycle, the epidermal cells (e.g., Raschke, 1979).decrease in leaf conductance is often Also, in most experiments under normalexplained as a function of the decrease in conditions, we are unable to uncouple theleaf water potential. During the last few decrease in leaf conductance and theyears, increasing evidence has been decrease in water potential; both are com-accumulated that stomatal closure at mon plant responses to drying soil. Leafdrying soil is not only related to a deterio- water relation parameters, however, failedration in shoot water potential but also to to explain the stomatal response due tochanges in soil conditions. In this paper, drought. Often there is no unique relation-we summarize the experimental evidence ship between leaf conductance and leafthat led us to hypothesize a communi- water potential for different species (e.g.,cation between root and shoot on drying Schulze and Hall, 1982). Some speciessoil. show a more linear relationship between Changes in plant performance with the two, others an expressed thresholddrying soil have been widely discussed response, which means that, during a soilduring the last 50 years. Martin (1940), drying cycle, leaf conductance was main-Veihmeyer and Hendrickson (1950), and tained at a high value until a critical leafVeihmeyer (1956) had previously con- water potential was reached (Turner,cluded that the rate of transpiration was 1974; Ludlow, 1980). However, Bates and surprising to see that the leaf conduc- that leaf conductanceHall (1981) showed, was tance of the single leaf was independent decrease without any detectablecan of its leaf water potential related to the soilchanges in bulk leaf water potential. Turn-er et al. (1985) and Gollan et aL (1985) water content (Fig. 1 ).showed for a herbaceous and a woody The conclusion of their experiments wasspecies, that within one species there was that the stomatal aperture is under the unique relationship between leafno control of signals from the root system thatconductance and leaf water potential with experiences the drying soil and is medi-drying soil. In their studies, leaf conduc- ated to the shoot via the transpirationtance of a single leaf was measured at stream.constant high humidity with the remainder The problem in working out controllingof the plant being either at high or low air factors on stornatal conductance at dryinghumidity ...