Carry-over effects of soil inoculation on plant growth and health under sequential exposure to soil-borne diseases

Abstract

Background and aims Most plant-soil feedback and inoculation studies are limited to one growth cycle. We examined the effects of inoculation with eight plantconditioned soils on chrysanthemum during two sequential growth cycles. The plants were also exposed sequentially to soil diseases. Methods In cycle 1, plants were grown in sterile soil inoculated or not with plant-conditioned soils, and exposed or not to Pythium or root feeding nematodes. In cycle 2, new plants were grown in soil from cycle 1 or in new 100% sterile soil. Plants were exposed again to Pythium, or to soil with pathogens and nematodes collected from a commercial chrysanthemum greenhouse. Results After two cycles, effects of soil inoculation on plant growth were still present. Chrysanthemum exhibited a negative conspecific feedback response, but this was less strong in inoculated soils. Pythium or nematode addition did not affect plant growth. However, addition of pathogen-containing soil from the commercial greenhouse reduced plant growth in sterile soil but increased growth in plant-conditioned soils. Conclusions Inoculation with plant-conditioned soil can reduce the negative conspecific plant-soil feedback of chrysanthemum. Our study further advances our understanding of the temporal dynamics of conspecific and heterospecific plant-soil feedbacks, and how they interact with soil-borne diseases.

Conditioning the soil microbiome through plant–soil feedbacks suppresses an aboveground insect pest

“…We hypothesized that every plant species would exert a specific effect on the microbiome in their soil. An important question is how this is maintained when another plant species grows in that soil later, as the latter plant also influences the soil microbiome (Ma et al ., ; Wubs & Bezemer, ). Here we show that chrysanthemum exerted a strong negative effect on fungi (especially on the Glomeromycotina, known as arbuscular mycorrhiza), as only 58% of the total fungal OTUs were present both in the inocula and in the soil after chrysanthemum growth (Fig.…”

“…Especially interesting are those inocula that led to a reduction in thrips without affecting plant growth, which was the case for soil inocula that consisted of RA‐ or HL‐conditioned soil (Figs , ). We expected that, in addition to increasing resistance, the selected species and especially grasses would promote chrysanthemum growth, based on our previous studies where chrysanthemum grew better in soils with those inocula than in sterilized soils (Ma et al ., , ). A possible explanation for the lack of plant growth promotion in inoculated soil in this study is that even for a single microbial strain, a common duality that is observed is that the establishment of symbiosis has a cost for the plant that might result in reduced growth (Morgan et al ., ), contributing to a spectrum of positive, neutral and negative effects of microbes.…”

Inoculum origin and soil legacy can shape plant–soil feedback outcomes for tropical grassland restoration

“…Spore diversity can be an important factor positively influencing mycorrhizal colonization (Fitzsimons & Miller 2010) and high spore loads can lead to elevated mycorrhizal colonization (Khakpour & Khara 2012). Ultimately, the origin of inoculated soil can affect the net plant response (Ma et al 2018), through directly influencing a plant's ability to recruit available microorganisms, as demonstrated here. However, we acknowledge that although our results point to a strong effect of mycorrhizal fungi on plant success, we did not collect the evidence to show that mycorrhizal fungi, rather than other organisms present in the soil, drove our results.…”

Soil Inoculation Alters Leaf Metabolic Profiles in Genetically Identical Plants

“…However other studies have shown that the composition of these soil microbiomes varies greatly from those in inoculated soils (e.g. Ma et al 2018 ). Therefore, we propose that the differences that we observed in metabolome composition were caused by differences in soil microbial communities in the different inocula.…”