Microbially-induced variation in allelopathy among old field plants

Background/Question/Methods

Soil microbes generate complex interactions that can directly and indirectly regulate plant communities and populations. While the importance of plant-microbe interactions have clearly been demonstrated, their role in plant-plant interactions have been explored in less detail.  This study specifically focused on determining the influence of soil microbial communities on allelopathic potential in old field plants.  Four species (two each of Aster and Solidago) were grown in a pot experiment and inoculated with each species’ soil microbial communities in all pair-wise combinations and with a sterilized inoculum.   To determine microbial source effects on allelopathic potential, leaf tissue from the pot experiment was used in a series of bioassays.  This design allowed us to test for the effects of microbial community identity on allelopathic potential within and between plant genera.  This experiment was followed by HPLC characterization of metabolites from leaf tissues to determine whether soil microbial communities resulted in altered chemical profiles for each species.

Results/Conclusions

Microbial communities induced changes in allelopathic potential in the target species and this induction varied among soil microbial sources. Overall Aster was less toxic than Solidago, though there was much variation among species-soil combinations.  When the data were pooled into four groups – sterile soil, self soil, congener soil (same genus, other species) and confamilial (both species from the other genus), patterns were much clearer.  The allelopathic potential of both interspecific soils (congener and confamilial) were indistinguishable from each other.  However, plants grown with sterile soil inocula had the greatest allelopathic potential, and plants grown in their own microbial communities had the lowest potential.  Metabolite profiles from HPLC analysis revealed significant variation among inoculum types, confirming that soil microbial communities resulted in altered chemical composition in these species.  These results suggest that soil microbial communities largely reduce the ability of plants to produce allelochemicals.  As growth of plants in their own soil did not differ from sterile controls in the original experiment, this response does not appear to be driven by greater inhibition by self soils.  In contrast, this may represent a level of self-recognition.