Premise of research.Arbuscular mycorrhizal fungi can colonize plants of different species, creating a common mycorrhizal network (CMN) connecting the roots of many plants. How the CMN affects plant performance, especially during early plant life stages, is still uncertain. We examined the seedling performance of two temperate forest wildflowers (Arisaema triphyllum and Maianthemum racemosum) with and without open access to a CMN produced by conspecific or heterospecific adult plants, under conditions of optimal watering and water stress.Methodology.We established a split-pot design, where the adult Arisaema or Maianthemum plants grew in the main portion of the pot and the seedlings of both species grew in the seedling pots within the main container but separated from the soil matrix by nylon membranes that permitted or prevented connection with the mycorrhizal network of the adult plants. We examined the seedling growth response, nutrient acquisition, and gas exchange after 3 yr of growth.Pivotal results.Connection with the CMN had little effect on seedling biomass but did result in higher seedling nutrient content. Adult plant identity affected the nutrient content for the Maianthemum seedlings. Adult plant identity did not directly affect the Arisaema seedlings, but connection with the CMN of a heterospecific adult improved leaf N content more than connection with the CMN of a conspecific adult. Water stress also impacted the seedlings differentlywater-stressed Arisaema seedlings had less seedling biomass, while water-stressed Maianthemum seedlings, for example, had higher nutrient content compared with well-watered plants. The Maianthemum seedlings also exhibited the highest gas exchange rates when grown under water stress with a heterospecific adult, regardless of their connection with the CMN.Conclusions.Our results suggest that the CMN may confer both positive and negative effects on seedling performance, but the direction and magnitude of the effects will vary between plant species and can be altered under environmental stress.
