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Soils contain biotic and abiotic legacies of previous conditions that may influence plant community biomass and associated aboveground biodiversity. However, little is known about the relative strengths and interactions of the various belowground legacies on aboveground plant–insect interactions. We used an outdoor mesocosm experiment to investigate the belowground legacy effects of range‐expanding versus native plants, extreme drought and their interactions on plants, aphids and pollinators. We show that plant biomass was influenced more strongly by the previous plant community than by the previous summer drought. Plant communities consisted of four congeneric pairs of natives and range expanders, and their responses were not unanimous. Legacy effects affected the abundance of aphids more strongly than pollinators. We conclude that legacies can be contained as soil 'memories' that influence aboveground plant community interactions in the next growing season. These soil‐borne 'memories' can be altered by climate warming‐induced plant range shifts and extreme drought. [ABSTRACT FROM AUTHOR]

Genetic diversity can have important ecological consequences on population dynamics and ecosystem functions and processes. While the direct effect of genetic diversity on population performance has been widely documented, its soil legacy effect has received little attention. To assess both the direct and soil legacy effects of genetic diversity on population performance, we conducted a plant-soil feedback experiment with 12 genotypes of a clonal plant Hydrocotyle vulgaris. We first conditioned soils (conditioning phase) by growing populations of H. vulgaris consisting of 1, 2, 4 and 8 genotypes in the soils and then tested the soils (test phase) by growing populations consisting of all 12 genotypes in sterilized bulk soils inoculated with each of the conditioned soils at a volume ratio of 10%. At the end of the conditioning phase, both biomass and the number of ramets of the populations of H. vulgaris first decreased and then increased with increasing genotypic diversity, indicating a direct effect of genetic diversity on population performance. At the end of the test phase, both biomass and number of ramets were significantly higher when the populations were grown in the soils conditioned by the populations consisting of 1 and 2 genotypes than when they were grown in the soils conditioned by the populations consisting of 4 and 8 genotypes, suggesting a soil legacy effect. Therefore, genetic diversity can have both a direct and a soil legacy effect on population productivity and size of H. vulgaris. These results highlight the importance of intraspecific differences on population performance and suggest that soil legacy effects should also be considered to fully understand the role of genetic diversity.