Manipulation of soil microbiome impacts arbuscular mycorrhiza colonization of plants: a study of the influences of the soil microbiome colonisation rates of arbuscular mycorrhiz colonization rates in sterilized and inoculated soils

Soils support complex microbial communities. Arbuscular mycorrhizal fungi (AMF) are important symbionts of many plant species, facilitating increased access to soil nutrients. Soil microbiome composition can impact AMF populations, affecting plant root colonization and plant growth. Here we evaluated the mycorrhiza colonization of two plants (Brachiaria sp. and Crotalaria sp.) cultivated in soils hosting distinct microbiomes. This glasshouse experiment used soils with eight distinct compositions of soil microbiomes: natural soil (i); soil exposed to heat treatments for one hour of 50 ºC (ii), 80 ºC (iii) or 100 ºC (iv); and sterilized soil (SS) followed by inoculation of dilutions of the natural soil community at: 10-1 (v), 10-3 (vi), 10-6 (vii), and SS without inoculation (viii). Microbial (bacteria and fungi) communities were assessed through 16S and ITS1 metabarcoding and the determination of the acid phosphatase activity. Sequencing results showed distinct microbial communities formed according to the soil manipulations and acid phosphatase activity declined along a stress gradient. Next, seedlings of Brachiaria and Crotalaria were transplanted to soils with separate inoculations of three AMF (Acalouspora colombiana, Rhizophagus clarus, and Dentiscutata heterogama), which were compared to an AMF-free control. Brachiaria showed higher colonization in natural soil when compared to other manipulations, regardless of the AMF species inoculated. Conversely, two mycorrhiza species were able to colonize Crotalaria under modified microbial communities in similar rates to natural soil. In summary, this suggests that Brachiaria was more dependent on the soil microbiome to promote root AMF colonization while Crotalaria relied on the AMF inoculations.