Senior Scientist The University of Kansas, United States
Background/Question/Methods The processes driving the functional benefits of biodiversity remains a critical, but unanswered question in both agriculture and ecology. We tested whether the soil microbiome mediated the productivity benefits of diversity among crops and in grasslands. Across both systems, we found evidence of productivity benefits of plant diversity being mediated by components of soil microbiome. We found that agricultural wheat/faba bean maize/faba bean intercropping altered the soil microbiome composition with relative abundance of putative pathogens decreased and relative abundance of Rhizobia increased. Suppression of pathogens in mixture contributed to overyielding. Moreover, the greater bacterial and fungal dissimilarities in heterospecific than host crop’s own soil, the better it improved crop growth, indicating the positive effect from alterations of soil microbial composition. In natural grasslands, we used late successional species combinations and found that the positive diversity-productivity relationships occurred with higher soil microbial diversity. That results from the operation of two microbial mechanisms: decrease of negative feedback effects induced by pathogens and increase of positive feedback effects from beneficial (AMF or rhizobial) microbes. In conclusion, both host-specific pathogens dilution/suppression and microbiome-mediated resource partitioning may act in concert to contribute to the positive diversity-productivity relationships in both agricultural intercropping and natural grassland ecosystems.
Results/Conclusions In both agricultural maize/faba bean and wheat/faba bean intercropping, soil microbes drove intercropping overyielding compared to monoculture, with 28%–51% of the overyielding contributed by microbial legacies. The overyielding effects resulted from negative PSFs in both systems, as crops, in particular faba bean grew better in soils conditioned by other crops than itself. More detailed analysis showed faba bean monoculture soil accumulated more putative pathogens with higher Fusarium relative abundance and more Fusarium oxysporum gene copies by qPCR, while in heterospecific soils, there were less pathogenic effects when cereals were engaged. In addition, at the low P level, AMF increased maize/faba bean intercropping overyielding, intercropped maize biomass and P uptake, while faba bean was not responsive to AMF inoculation. Similarly, we found the soil microbiome mediates the diversity-productivity relationships among late successional plant species, namely productivity increased with plant richness in diverse soil communities. Transgressive overyielding resulting from positive complementarity was only observed with the late successional soil microbiome, which was both the most diverse and exhibited the strongest microbial community differentiation among plant species. We found evidence that both dilution/suppression from host-specific pathogens and microbiome-mediated resource partitioning contributed to positive diversity-productivity relationships and overyielding.
