Percentage of rhizosphere bacterial isolates positive for different enzyme activities.

<p>Bacterial isolates were obtained from root-adhering soil after 6 weeks of growth of <i>Carex arenaria</i> seedlings in quartz sand microcosms. * indicates significant difference (p < 0.05) between microcosms with and without pre-inoculation of fungi. Note that experiment 1 and 2 started with different bacterial inoculums as indicated in Material & Methods. Data are the averages of three randomly selected sand microcosms. Error bars represent standard deviation. For each microcosm 40 bacterial isolates were individually screened for the different enzyme activities.</p

Schematic illustration of possible stimulation of biocontrol of soil-borne pathogenic fungi by increase of saprotrophic fungi.

<p>Organic amendments and/or other measures that stimulate growth of saprotrophic fungi can result in an increase of uptake of rhizodeposits by these fungi and, consequently, in an increase of competitive fungal pressure towards rhizosphere bacteria. As a result bacteria that are antagonistic against fungi will increase and several of these bacteria may also be antagonistic against soil-borne pathogenic fungi and form a natural barrier against fungal diseases. An advantage over introduction of antifungal biocontrol strains is that the fungus-induced stimulation occurs <i>in situ</i> with indigenous soil bacteria that are adapted to the local environmental conditions.</p

Bacterial numbers and fungal biomass (ergosterol) after 6 weeks of growth of <i>Carex arenaria</i> seedlings in quartz sand microcosms.

<p>1A: Number of bacterial colony forming units in the <i>Carex</i> rhizosphere (root-adhering sand); * indicates significant difference (p < 0.05) between microcosms with and without (control) the presence of inoculated fungi, # indicates p = 0.052 for Log-transformed data. 1B: Ergosterol concentrations. r indicates rhizophere sand (sand adhering to <i>Carex</i> roots), nr indicates sand remaining after removal of <i>Carex</i> roots. * indicates significant difference (p < 0.05) within fungal treatments between root-adhering and non-root-adhering sand. Data for both figures are the averages of 5 or 6 sand microcosms. Error bars represent standard deviation.</p

Pictures of the experimental set-up of sand microcosms with <i>Carex arenaria</i> (sand sedge) plants.

<p>Pictures of the experimental set-up of sand microcosms with <i>Carex arenaria</i> (sand sedge) plants.</p

Percentage of rhizosphere bacteria isolates with <i>in vitro</i> antagonistic activity against different fungi.

<p>Bacterial isolates were obtained from root-adhering soil after 6 weeks of growth of <i>Carex arenaria</i> seedlings in quartz sand microcosms. * indicates significant difference (p < 0.05) between microcosms with and without pre-inoculation of fungi, for the ANOVA test of data of the white column in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137988#pone.0137988.g003" target="_blank">Fig 3B</a> Log transformation was applied; # indicates p = 0.072. Note that experiment 1 and 2 started with different bacterial inoculums a as indicated in Material & Methods. Data are the averages of three randomly selected sand microcosms. Error bars represent standard deviation. For each microcosm 40 bacterial isolates were individually screened for in vitro antagonisms against the different fungi.</p

Appendix A. Additional methods (inverted assay and the volatiles analysis), results (pictures, rank abundance, heatmap, NMDS plots), and discussion (dilution approach).

Additional methods (inverted assay and the volatiles analysis), results (pictures, rank abundance, heatmap, NMDS plots), and discussion (dilution approach)