Soil microbial flora
Is a stable soil microflora harder to invade?

The greatest challenge to root colonization is the competitive advantage of the existing soil fungi. Three different  microbial flora have been established in the Rodale Farming Systems Trial which has been managed continuously for 18 years with mineral fertilizer, animal manure or legumes to supply nitrogen. All three management regimes have emphasized feeding and stabilizing soil fungi. The mycorrhizal fungi have been characterized by  David Douds and Marlise Snyder, USDA-ERRC. They found that Glomus spp. dominate with mineral fertilizer, whereas Gigaspora gigantea dominates the legume and manure-based regimes. Further, Jeff Buyer and Laurie Drinkwater (Rodale) have shown that the microbial communities vary in their ability to use different carbon sources. Therefore, there are three different stable microbial communities present in the same soil.  Presumably, even the strains of Trichoderma present in each one vary among the regimes.

In a common-garden experiment we examined whether the microbial flora affects the ability of Trichoderma to colonize.  The latter two provide more food for soil fungi. The results indicate that the animal based system is as easily colonized as the conventional one. Colonization was not significantly different among the management regimes.  Colonization was about 10-fold greater  following inoculation with T-22, demonstrating the consistently greater rhizosphere competence over the native strains.


The superior rhizosphere competence of T-22 allows it to colonize roots at 10 times the level found even in stable microbial communities.