A Comparison of Chemical Properties Between Gypsophile and Nongypsophile Plant Rhizospheres

Abstract

Soils with high gypsum content support specific vegetation, indicating a soil environment to which gypsophile plants have adapted. The goal of the present work was to compare the chemical composition, mainly the availability of micronutrients, of the rhizosphere soil of plants growing in gypsiferous soils to that of plants growing in nongypsiferous soils. Rhizospheres of populations of gypsophile (true and facultative) and nongypsophile plants were sampled, and concentrations of SO 2- 4 , Ca 2+ , Mg 2+ , K + , Fe, Cu, Mn, and Zn were determined. Sulphates and Ca 2+ concentrations were higher in the rhizosphere of gypsophile plants, either true and facultative, than in the rhizosphere of nongypsophile plants. The electrolytic conductivity (EC) is moderate in all cases (maximum 2.5dS m - 1 ), and pH values (between 7.6 and 7.9) were slightly basic and similar among the sampled rhizospheres. Largest differences were found in the micronutrient concentrations, especially Fe and Mn. Soils holding gypsophile plants had higher Fe concentration (4.03 µg g -1 ) than soils holding nongypsophile or facultative gypsophile plants (between 1.3 and 2.0 µg g -1 ). Soil holding facultative and nongypsophile plants showed an opposite behavior regarding Mn: low concentrations for true or facultative gypsophiles (1.3-2.6 µg g -1 ) and high concentrations for nongypsophile plants (5.8 µg g -1 ). Properties of bulk gypsiferous soils were also present at the rhizosphere level, suggesting that ecophysiological adaptation mechanisms, at the rhizosphere level, were not very active. A specific dynamic of micronutrients at the rhizosphere level, that might indicate the presence of some type of mechanism determining the availability of these elements, was not observed.