Figure 1.
Schematic diagram of the experimental setup.
Three matric potentials were combined with three sand particle size fractions with different pore size distributions, giving a total of nine treatments. In each box, the appropriate gravimetric water content of each treatment is indicated. Grain size, water distribution and bacterial cells (orange and purple) are indicated for illustrative purposes and are not based on actual microscopic visualization. Habitat connectivity decreases with decreasing matric potential and increasing pore size. In well-connected soils, (e.g. the treatments “wet” and/or “fine pores”), bacterial species (orange and purple) often inhabit connected microhabitats/pore spaces, thereby allowing for completive interactions. Under less-connected conditions (e.g. low matric potential “dry” and coarse pores), microhabitats are discontinuous, thereby reducing competitive bacterial interactions.
Figure 2.
Pore size distribution of the three sand size fractions (fine, medium, coarse).
Boxes indicate water-filled pores at different matric potentials, i.e. in the “dry” treatments all pores with a pore-neck diameter < = 6 µm are filled with water, in the “intermediate” treatments < = 15 µm and in the “wet” treatments < = 30 µm, respectively. Pores above these pore-neck diameters are filled with air.
Figure 3.
Expansion of Streptomyces and Bacillus inoculated individually in nine different combinations of pore size distribution and matric potential.
Each data point represents the mean of 2 replicate microcosms with 4 measurements per microcosm. Error bars show the standard deviation.
Table 1.
Three-way ANOVA of factors affection expansion of bacteria in sand microcosms.
Figure 4.
Population dynamics of Streptomyces and Bacillus competing in nine different combinations of pore size distribution and matric potential.
The x-axis is time in days and the y-axis is cell number (g drywt soil) on a log-scale. Each data point is the mean of three microcosm replicates. Error bars show the standard deviation.
Table 2.
Three-way ANOVA of factors affecting Bacillus/Streptomyces (B/S) ratios.
Table 3.
Three-way ANOVAs of factors affecting population densities of Bacillus and Streptomyces strains after the given periods of incubation.