What happens next? Legacy effects induced by grazing and grass-endophyte symbiosis on thistle plants and their floral visitors

Abstract

Background and aims: Complex webs of multiple interactions determine the final aboveground and belowground community structure. While the mechanisms are difficult to determine, soil conditioning may modify other plants performance and their interaction with other organisms. We aim to determine the extent to which aboveground Epichloë endophytes and consumers induce legacy effects on subsequent plants and their interactions with floral visitors. Methods: We performed two mesocosm experiments in two phases. Firstly, annual ryegrass plants (Lolium multiflorum), in symbiosis or not with Epichloë occultans and subjected or not to grazing, were grown in mesocoms to generate four soil conditionings. Secondly, thistle plants (Carduus acanthoides) were grown in these conditioned soils. We assessed thistle plants aerial biomass, number of flower heads and their floral visitors. Results: The presence of one or both interactions (symbiosis and grazing) reduced total visits in subsequent thistle plants by 45 %. In particular, honeybees and other bees were reduced by 42 and 51 %, respectively. The flower head number or biomass of thistle plants may only partially mediate these effects. Conclusions: To better understand the rules structuring communities and ecological processes, it is critical to connect multiple interactions effects on soil conditions and their influence on trophic and non-trophic interactions during the subsequent generations.