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Response of Sorghum and Wheat to Different K + /Na + Ratios at Varying Osmotic Potentials 1
Author(s) -
Devitt D.,
Stolzy L. H.,
Jarrell W. M.
Publication year - 1984
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj1984.00021962007600040040x
Subject(s) - sorghum , shoot , osmotic pressure , xylem , salinity , chemistry , plant physiology , osmosis , horticulture , nutrient , agronomy , botany , biology , ecology , biochemistry , organic chemistry , membrane
Plants growing in saline‐sodic conditions must confront not only osmotic stress but the relative toxicity of the Na ion. The impact of these two factors on the physiology and morphology of the plant will often determine the plant growth in saline‐sodic soils. The objective of this experiment was to investigate the impact of low K + /Na + ratios at given osmotic potentials in the solution phase on cation composition in the plant tissue, stomatal response, and root growth and development. The experiment was conducted in outdoor solution culture tanks. Wheat ( Triticum aestivum ) and sorghum [ Sorghum bicolor (L.) Moench] were grown for 6 weeks in nutrient solution to which a range of polyethylene glycol 6000 and/or NaCl additions were made (MPa = −0.070, −0.076, −0.193, −0.340, −0.493 and K + mmol L −1 /Na + mmol L −1 = 1/0,1/1,1/10,1/25,1/60,1/100). Porometry measurements were taken twice weekly at 830 and 1230 h. Leaf xylem water potentials were measured at 1230 h. Root length extension, root volume solution displacement and solution samples were taken weekly over the 6 week experimental periods. At harvest, fresh and dry weights were measured and the plants were subdivided into roots, shoots, stalks, and leaves for eventual analysis of Na, K, Ca, and Mg. Diffusive resistances generally increased with decreasing osmotic potential for both sorghum and wheat; however, measurement variability prevented clear separation between all osmotic and K + /Na + treatments. The highest diffusive resistances were measured in plants grown in the −0.493 MPa, K + /Na + = 1/100 solution. Interpolated Na + concentrations in the plant tissue from estimated growth and Na uptake curves suggested translocation of Na to the upper leaves coincident with the stomatal response. The Ca concentration in the upper leaves decreased as Na increased. The combination of high Na and low Ca concentrations in the leaves, even when K concentrations appeared to be adequate, apparently decreased effective regulation of the stomata in the sorghum treatment. Root mass decreased as the osmotic potential of the solution decreased, while root elongation was primarily dictated by the Na concentration in solution. Sorghum root elongation decreased while wheat root elongation increased as the Na concentration increased within each osmotic level. Sodium was primarily confined to the root system in sorghum but translocation to the tops increased as the Na concentration increased. With wheat, Na was not restricted to the root system. An excellent exponential relationship for sorghum was found between the coefficient of root elongation and the concentration of Na in the plant. Root elongation of both wheat and sorghum under saline‐sodic conditions is controlled to a great extent by the degree of Na saturation of the root tissue.