INFLUENCE OF PLANTS AND CROPPING ON MICROBIOLOGICAL CHARACTERISTICS OF SOME NEW CALEDONIAN ULTRAMAFIC SOILS

Five New Caledonian ultramafic soils were compared for their bacterial and fungal population densities and for their microbial activity esti mated by fluorescein diacetate (FDA) hydrolysis. The low microbial num bers and activities were related to the organic matter content and to metallic toxicity. Actinomycetes were found to be dominant among bacte rial populations. The effect of soil colonisation by plants on the mic roflora was studied and appeared to be very favourable. The rhizospher e effect of 2 plant species (Grevillea gillivrayi and Costularia comos a) was estimated. The influence of cropping on the development of micr oflora in one soil was also investigated and a qualitative study of th e fungal populations and their variation in relation to the cropping w as reported. The fungal flora was dominated by Moniliaceae, and Tuberc ulariaceae and Dematiaceae were absent in natural ultramafic soils. Cr opping enhanced the diversity of these fungal populations.