Insects and mycorrhizal fungi influence maternal seed provisioning in Senecio vulgaris

The performance of plants in any one generation can be influenced not just by the prevailing biotic and abiotic factors, but also by those factors experienced by the parental generation. These maternal effects have been recorded in an array of plant species, but most studies tend to focus on abiotic factors over two generations. Here we show that maternal effects in the annual forb Senecio vulgaris may be influenced by beneficial arbuscular mycorrhizal fungi and insect herbivory over four successive generations. These effects were very much determined by seed provisioning, wherein C:N:P ratios were altered by both fungi and aphids. There was little evidence of epigenetic changes induced by the fungi or insects, instead the driving forces seemed to be allocation of N and P to the seeds. However, changes in seed chemistry were not cumulative over generations, often decreases in seed nutrient content were followed by recovery in subsequent generations. The changes in seed stoichiometry can have important consequences for viability, germination and subsequent seedling growth rates. We conclude that studies of maternal effects need to be conducted over multiple generations, and also need to be multifactorial, involving variation in abiotic factors such as water and nutrients, combined with biotic factors.