EFFECTS OF PLANT SOCIAL ENVIRONMENT ON THE MUTUALISTIC INTERACTIONS BETWEEN PLANTS AND MYCORRHIZAL FUNGI

Abstract

<p>Plants and mycorrhizal fungi form a mutualism in which plants donate carbon to the fungus and, in return, receive benefits such as increased nutrient uptake and water. Mycorrhizal fungi colonize plant roots, forming nutrient exchange structures. The fungi also colonize the soil by growing long strands of hyphae that forage for nutrients and attach plants, forming a common mycorrhizal network (CMN). Plants attached to a well-supported CMN will receive greater benefits than those attached to a lesser CMN because the more carbon donations the fungal partner receives, the more it can grow and colonize the soil, accessing hard to reach soil nutrients. Kin selection theory predicts that relatives should donate more carbon to the fungal partner than non-relatives because benefits gained by neighbouring relatives through the CMN lead to inclusive fitness gains. Thus, social environment, i.e. relatedness of the group, could affect the mycorrhizal mutualism. Moreover, the presence of mycorrhizal fungi in the soil could affect plant responses to their social environment.</p> <p>For my PhD thesis I have investigated whether mycorrhizal fungi respond to plant social environment and whether the presence of mycorrhizal fungi affects plant responses to relatedness. I have addressed these topics in three greenhouse studies and two field studies, using herbaceous plants and trees. I have found strong evidence that siblings have an increased association with their mycorrhizal partner compared to strangers, resulting in greater benefits for siblings. Taken together, the results from this thesis demonstrate that the ability for plants to recognize kin has implications beyond intra-specific competitive interactions and that plant social environment has important effects on a widespread inter-specific mutualism. Additionally, the recently discovered phenomenon of plant kin recognition has been put into the context of mycorrhizae, and I have shown that mycorrhizal plants respond differently to their social environment than non-mycorrhizal plants.</p>