PRINCIPAL COMPONENTS-ANALYSIS OF THE SOIL MICROBIAL-POPULATION OF HUMID ZONE OF GALICIA (SPAIN)

Principal components analysis has been applied to the total microbial population numbers and to taxonomic groups and the physiological groups involved in the C, N and S cycles in 10 humid zone soils developed over 7 different types of rock, the aim being to determine the relationships between the various groups and the factors influencing the distribution of microflora in these soils. Except for fungi, which are negatively correlated with certain other groups (algae especially), all the remaining groups are either not correlated or positively correlated with each other. The factor most influencing the density and functional diversity of the microbial population is depth within the profile, both density and diversity decreasing with increasing depth. In the surface horizons the distribution of microflora is controlled by the time of year and the associated changes in climatic conditions, with lack of humidity limiting the microbial population more than temperature. The time of year likewise determines the proteolytic and ammonification potential, whereas nitrification depends on the degree of differentiation of the profile. Denitrification and aerobic and anaerobic nitrogen fixing potential appear to be controlled by pH. Aerobic cellulolysis potential depends on the degree of evolution of the profile, with greatest potential in the least evolved soils, whereas the distribution of anaerobic cellulolytics seems to be determined by the type of parent rock. © 1990.