Soil microorganisms can affect ecologically important plant traits, including resistance to insect herbivores. We previously found that soil microbiomes shift over the course of fallow/oldfield succession, altering the community that assembles in the rhizosphere of a native plant, goldenrod, Solidago altissima (Asteraceae). These successional microbial shifts can be functional, as inoculating S. altissima plants with late succession (15 years fallow) microbial communities conferred greater resistance to their primary herbivore, Trirhabda sp. (Chrysomelidae), than their counterparts grown in early succession (2 years fallow) microbiomes. This microbially-mediated successional trend in herbivore resistance parallels patterns of resistance observed in the field, suggesting that shifts in soil microbial communities over succession may play an important role in driving changes in resistance. However, whether these microbial shifts affect the herbivore resistance of other plant species is unknown. Here we investigated the effects of soil microbiomes from agricultural fields and different stages of succession (1, 3, and 16 years fallow), collected from a large-scale field experiment, on the growth and pest resistance of four crops: maize, tomato, cucumber, and lettuce. We inoculated the crops with these different microbiomes in a greenhouse mesocosm experiment and compared their resistance to two generalist pests, Trichoplusia ni and Spodoptera frugiperda.
Results/Conclusions
We found that microbiomes from fallow agricultural fields altered the growth and pest resistance of plants, but the effects were species-specific. For example, lettuce produced the largest leaves when inoculated with a 3-year fallow microbiome, the microbiome in which cucumber performed worst, while tomato growth was unaffected under any microbiome treatment. Maize grew largest inoculated with the 16-year fallow microbial community. Consistent with the pattern we observed in S. altissima, plants were generally more resistant to T. ni when inoculated with the later succession microbiomes, particularly in contrast to those treated with agricultural microbiomes. However, for tomato plants, the opposite pattern was observed with regard to S. frugiperda resistance. Collectively, these results indicate that plant responses to microbiomes are species-specific and emphasize the need characterize the responses of taxonomically and functionally diverse plant species to different microbiomes. Yet, we found that microbiomes from fallow fields have the potential to affect agronomically important crop traits and as farmers incorporate fallow land into their landscape for other ecosystem services (e.g., habitat for pollinators and natural enemies of pests), assessing the soils of these communities as sources of functional microbiomes may reveal additional benefits.