Soil microbiomes harbor an extremely rich diversity of bacteria and fungi. Plants also have microbiomes, and as they are rooted in the soil, a subset of the soil microbiome colonizes the roots. Consequently, aboveground plant parts, such as stems and leaves, are inhabited by specific commensal, symbiotic or pathogenic bacteria and fungi that, at least partly, originate from the roots and soil.

Herbivorous insects ingest microorganisms that are present in the plant, and hence microorganisms that originate from the soil, via the plant, can be incorporated in the microbiome of the insect. However, whether herbivorous insect microbiomes as a whole are also influenced by the soil environment is unknown.  

In a recent study published in Nature Communications, four ecologists from Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology of Chinese Academy of Sciences, and Netherlands Institute of Ecology (NIOO-KNAW), addressed how plant-mediated changes in soil microbiomes affect plant and insect microbiomes in the context of aboveground-belowground interactions. 

Scientists first generated plant-conditioned soils in field plots, and reared leaf-feeding caterpillars on dandelion grown in these soils, to assess whether the microbiomes of the caterpillars were attributed to the conditioned soil microbiomes or the dandelion microbiome.

They found that microbiomes of caterpillars kept on intact plants differed from those of caterpillars fed detached leaves collected from plants growing in the same soil. Microbiomes of caterpillars reared on detached leaves were relatively simple and resembled leaf microbiomes, while those of caterpillars from intact plants were more diverse and resembled soil microbiomes.

Moreover, plant-mediated changes in soil microbiomes were not reflected in the phytobiome but were detected in caterpillar microbiomes, however, only when kept on intact plants.

These results implied that insect microbiomes depend on soil microbiomes, and that effects of plants on soil microbiomes can be transmitted to aboveground insects feeding later on other plants.