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 fluor escens strain Pf-5, biocontrol agents for Pyrenophora tritici-repentis , a straw-borne phytopathogen. The inoculated straw was exposed to alt ernate wetting and drying for 7 weeks to assess the effects of intenti onally applied microorganisms on selected ecological parameters of the plant litter microflora. Pseudomonas fluorescens had little effect, b ut 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 adequa te moisture (- 0.1 MPa) was increased in straw colonized by L. roseipe llis, but respiration at - 7 MPa was unaffected. The spectrum of sole carbon sources utilized by the straw microflora was altered slightly i n Limonomyces-treated straw. These observations provide a basis for fu rther studies concerning inoculant-induced ecological effects under fi eld conditions.