Data from: Soil pathogen-aphid interactions under differences in soil organic matter and mineral fertilizer

There is increasing evidence showing that microbes can influence plant-insect interactions. In addition, various studies have shown that aboveground pathogens can alter the interactions between plants and insects. However, little is known about the role of soil-borne pathogens in plant-insect interactions. It is also not known how environmental conditions, that steer the performance of soil-borne pathogens, might influence these microbe-plant-insect interactions. Here, we studied effects of the soil-borne pathogen Rhizoctonia solani on aphids (Sitobion avenae) using wheat (Triticum aestivum) as a host. In a greenhouse experiment, we tested how different levels of soil organic matter (SOM) and fertilizer addition influence the interactions between plants and aphids. To examine the influence of the existing soil microbiome on the pathogen effects, we used both unsterilized field soil and sterilized field soil. In unsterilized soil with low SOM content, R. solani addition had a negative effect on aphid biomass, whereas it enhanced aphid biomass in soil with high SOM content. In sterilized soil, however, aphid biomass was enhanced by R. solani addition and by high SOM content. Plant biomass was enhanced by fertilizer addition, but only when SOM content was low, or in the absence of R. solani. We conclude that belowground pathogens influence aphid performance and that the effect of soil pathogens on aphids can be more positive in the absence of a soil microbiome. This implies that experiments studying the effect of pathogens under sterile conditions might not represent realistic interactions. Moreover, pathogen-plant-aphid interactions can be more positive for aphids under high SOM conditions. We recommend that soil conditions should be taken into account in the study of microbe-plant-insect interactions.

越来越多的证据表明，微生物可调控植物与昆虫的互作（plant-insect interactions）。多项研究证实，地上病原菌（aboveground pathogens）能够改变植物与昆虫间的相互关系。然而，目前学界对土传病原菌（soil-borne pathogens）在植物-昆虫互作中的作用仍知之甚少，且尚不明确调控土传病原菌生长活性的环境条件，会如何影响这些微生物-植物-昆虫三方互作。
本研究以小麦（Triticum aestivum）为宿主植物，探究土传病原菌立枯丝核菌（Rhizoctonia solani）对麦长管蚜（Sitobion avenae）的影响。我们通过温室实验，设置不同梯度的土壤有机质（soil organic matter, SOM）与肥料添加量，探究其对植物-蚜虫互作的调控作用。为探明原有土壤微生物组（soil microbiome）对病原菌效应的影响，我们分别采用未灭菌的田间土壤与灭菌后的田间土壤开展实验。
在低土壤有机质含量的未灭菌土壤中，立枯丝核菌的接种会抑制蚜虫生物量；而在高土壤有机质含量的未灭菌土壤中，该病原菌则可提升蚜虫生物量。但在灭菌土壤中，立枯丝核菌的接种与高土壤有机质含量均会提升蚜虫生物量。肥料添加可提升植物生物量，但仅在土壤有机质含量较低，或未接种立枯丝核菌的情况下有效。
本研究表明，地下病原菌能够影响蚜虫的生长表现，且在无原有土壤微生物组的条件下，土壤病原菌对蚜虫的效应会更为积极。这意味着，在无菌条件下开展的病原菌效应相关实验，可能无法反映真实的自然互作过程。此外，在高土壤有机质条件下，病原菌-植物-蚜虫的三方互作对蚜虫更为有利。我们建议，在开展微生物-植物-昆虫互作相关研究时，应将土壤条件纳入考量范畴。