Frequencies, Microclimate and Root Properties for Three Codominant Perennials in the Northwestern Sonoran Desert on North-vs.South-facing Slopes

At a site in the northwestern Sonoran Desert the percent groundcover for the C₃subshrubEncelia farinosawas eight-times higheron more arid 20° south-facing slopes than on 20° north-facingslopes at 820 m elevation, and was six-times higher on north-facingslopes at a 300-m-lower elevation, also the more arid condition.The ground cover of the C₄bunchgrassPleuraphis rigidadecreasedover 50% from 20° north-facing slopes to the more arid conditionsof a 36° north-facing slope, a 20° south-facing slopeand a 20° north-facing slope at a 300-m-lower elevation.The CAM leaf succulentAgave desertialso had greater ground coverfor the 20° north-facing slopes at 820 m compared with 520m. For these three codominants that averaged 58% of the totalground cover, the key for the relative frequency ofE. farinosawasapparently its greater root growth on the warmer slopes duringthe winter. The key for the other two species was most likelysoil water availability, especially during the seedling stageforA. deserti. The wetter soil conditions on 20° north-facingslopes at 820 m apparently led to individual plants ofP. rigidathatwere twice as large as on south-facing slopes. Thus root propertiesmay exert the primary influence on relative plant frequencyin this desert ecosystem for which soil temperature and wateravailability are crucial.Copyright 1997 Annals of Botany Company Agave deserti; Encelia farinosa; Pleuraphis rigida; rooting patterns; soil temperature; Sonoran Desert; water availability     

The Saprophytic Status of Fusarium oxysporum Schl: Causing Vascular Wilt of Oil Palm

The droplet plating method described, especially when used inconjunction with a baiting technique, facilitates the demonstrationof Fusarium oxysporum in soil. This fungus was present in soilfrom wilt-free areas of oil palm plantations as well as in soilabout wilt-diseased palms. Hyphal fusions between soil isolatesand isolates from wilted palms could be demonstrated. The funguspersisted for periods of at least ¹ year in naturally infestedsoils under a variety of moisture conditions; it also survivedin inoculated alien soil forms of Ieast ¹year. Soil forms ofthe fungus had a high competitive saprophytic ability, competitivelycolonizing sterilized soils and sand, and organic materialsadded to soils and mixed cultures. The pathogenic isolate, aswell as the soil isolates, exhibited characters belonging tosoil-inhabiting fungi, namely continued persistance in soil:tolerance, in respect of growth and reproduction, to antagonism:and the ability competitively to colonize dead organic materialin soils. The pathogenic form is considered to be a soil inhabitant.