Linking intraspecific variation in plant chemical defence with arthropod and soil bacterial community structure and N allocation

Aims We tested whether chemical content of individual Tansy plants influences aboveground arthropod and belowground soil microbial community composition. Methods We use Tansy chemical defence composition as focus for our analysis, given that changes in chemical defence are a dominant mechanism expected to modify aboveground and belowground community composition and nutrient cycling. Detailed assessment of arthropod food webs were made on tansy chemotypes. Next generation soil DNA analyses were used to assess soil bacterial community. Results Tansy plants defended by Camphor and Borneol had higher total soil bacterial diversity than control plants (soils under non-Tansy plants) and Tansy chemotypes containing high concentrations of Thujon. Furthermore, the frequency of bacterial genera with a significant role in litter mineralization processes decreased with time in soil associated with Camphor and Borneol chemotypes, indicative of complete microbial decomposition and mineralization of plant material. No such changes occurred in soils associated with Thujon chemotypes. Thujon plants had fewer aphids, ladybirds, spiders, and Orius sp. than other chemotypes. Conclusions Our experiments revealed that Thujon chemotypes had different associated aboveground arthropod and belowground soil microbial communities than Camphor or Borneol chemotypes. The common qualitative response between aboveground and belowground communities to Tansy plant defense is consistent with our hypothesis and extensive literature on plant defense and aboveground and belowground feedbacks.