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The role of plant-soil feedback dynamics in determining plant community composition has been increasingly recognized. In both temperate grasslands and species-rich tropical forests, native species tend to experience negative feedback (soil microbial communities (SMC) in the rhizosphere of each species have a greater detrimental effect on conspecifics than on heterospecifics), whereas exotic invasive species often show positive feedback (SMC of each species have a greater detrimental effect on heterospecifics than on conspecifics) that promotes their invasive potential. However, it remains unknown how these interactions might change in human-modified landscapes consisting of habitats differing in native species diversity. We used a factorial greenhouse experiment to test plant-soil feedback for 8 native forest plant species and 2 widely planted exotic crop species in a montane region of Colombia to address two questions: 1) What type of feedback occurs in forest fragments and agricultural monocultures (pastures and coffee plantations)? 2) How does feedback differ between arbuscular mycorrhizal fungi (AMF) compared to non-AMF soil microbes? To do this, we inoculated each plant species with either AMF spore-cultures or a microbial filtrate amplified on each of the 10 inoculated with SMC from their respective habitats (e.g. native plants with SMC from forests, coffee with SMC from coffee plantations).
Results/Conclusions
Most native forest species from forest fragments showed negative feedback with AMF cultures (6 out of 8 species) and with the soil microbial filtrate that contained soil pathogens (6 out of 8 species). Surprisingly, Brachiaria brizantha (invasive exotic grass that dominates pastures) and Coffea arabica (coffee, an exotic non-invasive shrub) also experienced negative feedbacks for both AMF and the microbial filtrate, instead of positive feedbacks shown for temperate invasive exotics in other studies. For instance, feedback for B. brizantha and native species was mostly negative for AMF (5 out of 8 species) and the microbial filtrate (all species). Similarly, feedback between C. arabica and native species was mostly negative for AMF (5 out of 8 species) and the microbial filtrate (6 out of 8 species). Overall, feedback mediated by AMF was much weakly negative than feedback mediated by the microbial filtrate. These results suggest that plants in both natural forest fragments and species-poor agricultural lands show negative plant-soil feedback dynamics. Thus, it seems like soil organisms are widespread across habitat types with contrasting plant diversity and management regimes, where they might have significant effects on plant community composition.
