Microbial community structure and activity in wheat straw after inoculation with biological control organisms

Wheat straw on pans of soil in a greenhouse was inoculated with either the fungus Limonomyces roseipellis or the bacterium Pseudomonas fluorescens strain Pf-5, biocontrol agents for Pyrenophora tritici-repentis, a straw-borne phytopathogen. The inoculated straw was exposed to alternate wetting and drying for 7 weeks to assess the effects of intentionally applied microorganisms on selected ecological parameters of the plant litter microflora. Pseudomonas fluorescens had little effect, but L. roseipellis had measurable effects on some aspects of microbial community structure and function. The frequency distribution of fungal taxa on straw was altered by L. roseipellis, with a large increase in yeasts and a decrease in several filamentous fungi. Compared with non-treated straw, respiration (CO2 evolution) under conditions of adequate moisture (- 0.1 MPa) was increased in straw colonized by L. roseipellis, but respiration at - 7 MPa was unaffected. The spectrum of sole carbon sources utilized by the straw microflora was altered slightly in Limonomyces-treated straw. These observations provide a basis for further studies concerning inoculant-induced ecological effects under field conditions.