Lognormal Distribution of Bacterial Populations in the Rhizosphere

Abstract

Rhizosphere bacterial populations were estimated on 43 sets of up to 60 entire root systems of young greenhouse and field-grown plants (potato, sugar beet, barley, tomato or radish). Total aerobic bacterial populations, total fluorescent bacterial populations, and populations of inoculated plant growth-promoting strains of Pseudomonas putida or P. fluorescens generally approximated a lognormal distribution as determined by several graphic and statistical tests of normality (Rankit diagrams, Shapiro-Wilk tests and Kolmogorov tests). Total bacterial populations and populations of fluorescent pseudomonads varied by a factor of 10 to 50 within a given set of root systems. Seed piece or seed populations of inoculated rhizobacterial strains A1 or SH5 varied by a factor of 4-34, respectively; rhizosphere populations of these strains on potato or sugar beet varied by a factor of 100-1000. Populations of these inoculated strains of Pseudomonas on seed or seed pieces also approximated a lognormal distribution.