Abstract
The use of belowground microorganisms in agriculture, with the aim to stimulate plant growth and improve crop yields, has recently gained interest. However, few studies have examined the effects of microorganism inoculation on higher trophic levels in natural conditions. We examined how the diversity of phytophagous insects and their natural enemies responded to the field-inoculation of soybean with a model arbuscular mycorrhizal fungus (AMF), Rhizophagus irregularis, combined with a nitrogen-fixing bacterium, Bradyrhizobium japonicum, and a plant growth-promoting bacterium, Bacillus pumilus. We also investigate if the absence or presence of potassium fertilizer can affect this interaction. We found an increase in the abundance of piercing-sucking insects with the triple inoculant irrespective of potassium treatment, whereas there were no differences among treatments for other insect groups. A decrease in the abundance of the soybean aphid, Aphis glycines, with the double inoculant Rhizophagus + Bradyrhizobium was observed in potassium enriched plots and in the abundance of Empoasca spp. with potassium treatment independent of inoculation type. Although it was not possible to discriminate the mycorrhization realized by inoculum from that of the indigenous AMF in the field, we confirmed global negative effects of overall mycorrhizal colonization on the abundance of phytophagous piercing-sucking insects, phytophagous chewing insects, and the alpha diversity of phytophagous insects. In perspective, the use of AMF/Rhizobacteria inoculants in the field should focus on the identity and performance of strains to better understand their impact on insects.
Highlights
Plant beneficial soil microbes, including mycorrhizal fungi and plant growth-promoting rhizobacteria (PGPR), have long been studied and applied for their positive effects on plant growth, nutrient mobilization, and agricultural product yield [1,2]
We examined the effects of a combined inoculation of the Arbuscular mycorrhizal fungi (AMF) Rhizophagus irregularis isolate DAOM 197198
There were no significant differences between inoculant treatments (C, MR, MRB) for AMF colonization of roots or crop yield irrespective of potassium (Table 2)
Summary
Plant beneficial soil microbes, including mycorrhizal fungi and plant growth-promoting rhizobacteria (PGPR), have long been studied and applied for their positive effects on plant growth, nutrient mobilization, and agricultural product yield [1,2]. Arbuscular mycorrhizal fungi (AMF), of the phylum Glomeromycota [3,4], form one of the most widespread symbiotic associations with plant roots and constitute an important functional group in terrestrial ecosystems. Canada (NSERC) Discovery grants to CF (RGPIN 2017-06287) and to MH (RGPIN-2018-04178). EED received a scholarship from the Islamic Development Bank to support education fees and living allowances. Premier Tech Biotechnologies provided the seeds and inoculants and, in collaboration with La Coop Federee, the access to fields trials in for data collection
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