A wax-based antitranspirant (AT) was sprayed on leaves of three phreatophytes, salt cedar (Tamarix sp.), cottonwood (Populus sp.), and willow (Salix sp.), as an alternative to eradicating them to conserve water. Scanning electron micrographs gave information on the nature of the foliar surfaces and coverage by the AT wax. A 10% solution of AT (vol/vol) reduced the transpiration rates of container-grown phreatophytes by 35-75% 1 day after spraying and by 17-56% after 4 days. In gas exchange studies with salt cedar in the field, transpiration was reduced 40% by a 'light' application of 6% AT and 70% by a 'heavy' application. The AT also increased resistance to water vapor diffusion and the water potential of the sprayed leaves. On salt cedar, phytotoxicity occurred at high temperature and solar radiation only if spray applications were very heavy. The AT conserved water much more effectively when it was applied to the outer part of the canopy than when it was applied to the inner shaded foliage, where transpiration was already minimal. These data from sprays applied from the ground provided a basis for trials of AT application by aircraft.

No abstract

The use of monomolecular films of high alcohols to reduce evaporation from open water surfaces has stimulated much work on the possibility of applying these materials to plants to reduce transpiration. The results of 17 such investigations indicate that at concentrations that reduce transpiration, these materials also redue• plant growth. The one study that reported reduction of plant transpiration and increase of growth was repeated, but with negative results. Analysis of the relative resistances of hexadeeanol films to flow of CO,and water vapor and their relation to resistances to flow normally found in plant leaves indicates that these films should reduce photosynthesis more than transpiration. It is concluded that such materials are not suitable as antitranspirants. (Key words: Evapotranspiration; plants; vegetation) Considerable attention has been given in recent years to the reduction of reservoir evaporation by the application of higher aleohols to the surface of the water [La Met, 1962]. The hydrophylie ends of the long chain alcohol molecules are attracted to the water, and the hydrophobie ends are repulsed. Van der Wall forces cause a tightly and symmetrically arranged monomoleeular layer to form, which is highly impermeable to water vapor. It has been considered possible that such materials, if made to form a film on the mesophyll surface of plants, would constitute effective antitranspirants.Research in this direction was stimulated by W. J. Roberts [1961], who reported that. radioactively tagged hexadecanol was absorbed through corn roots, transported to the leaves, and reduced transpiration (see Table 1). How-

No abstract

No abstract