ALTITUDINAL GRADIENTS OF NUTRIENT SUPPLY TO PLANT ROOTS IN MOUNTAIN SOILS

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Abstract
Avena fatua, wild oats, was greenhouse grown in surface and subsurface soils collected on an altitudinal transect in the San Jacinto Mountains in southern California to assess patterns of nutrient supply. Concentrations of available Na, K, Ca, and Mg generally increased toward lower elevations in this gradient from cool moist to hot dry climates. Nutrient concentrations and uptake by Avena also increased with decreasing altitude but with different relative slopes than those of soil nutrients or nutrients in native plant leaves. Magnesium supply and uptake by root interception and supply by mass flow were greater in mid-elevations, while supplies and uptakes of Na, K, and Ca increase linearly toward low elevation. Calculated supplies of Na, Ca, and Mg exceeded uptake, producing large apparent accumulations about roots, but inadequate mass flow plus interception led to apparent depletion of K in the rhizosphere. Diffusion is the major mode of supply of K, interception for Ca, and interception plus mass flow for Na and Mg. The significance of these observations is interpreted for native plants growing on the transect from desert to chaparral, woodlands, and forests. Avena fatua, wild oats, was greenhouse grown in surface and subsurface soils collected on an altitudinal transect in the San Jacinto Mountains in southern California to assess patterns of nutrient supply. Concentrations of available Na, K, Ca, and Mg generally increased toward lower elevations in this gradient from cool moist to hot dry climates. Nutrient concentrations and uptake by Avena also increased with decreasing altitude but with different relative slopes than those of soil nutrients or nutrients in native plant leaves. Magnesium supply and uptake by root interception and supply by mass flow were greater in mid-elevations, while supplies and uptakes of Na, K, and Ca increase linearly toward low elevation. Calculated supplies of Na, Ca, and Mg exceeded uptake, producing large apparent accumulations about roots, but inadequate mass flow plus interception led to apparent depletion of K in the rhizosphere. Diffusion is the major mode of supply of K, interception for Ca, and interception plus mass flow for Na and Mg. The significance of these observations is interpreted for native plants growing on the transect from desert to chaparral, woodlands, and forests. © Williams & Wilkins 1977. All Rights Reserved.

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