Cheating belowground interactions : diversity, ecology and distribution of mycoheterotrophy

Mycoheterotrophy is a particular mode of life in which plants obtain carbohydrates from their associated fungal partners, instead of by using photosynthesis. Due to the complexity of mycorrhizal interactions and challenges in assessing the outcomes of this symbiosis, cheating has remained a poorly researched topic in plant ecology. This thesis aimed to shed light on the diversity, ecology and distribution of mycoheterotrophic interactions. In my approach, I considered that different drivers may be important at different scales and studied four levels of ecological complexity. In chapter 2, the specificity of mycoheterotrophic interactions within the arbuscular mycorrhizal symbiosis was assessed at the organism level. In chapter 3, biotic interactions between plants and fungi were studied in the framework of mycoheterotrophic plant coexistence scenarios at the population level. In addition, edaphic abiotic factors potentially influencing the occurrence of mycoheterotrophic plants were assessed at the community level in chapter 4, through a comparison of soil chemistry and nutrients in plots where mycoheterotrophic plants were present with those lacking these plants. Finally, in chapter 5 I derived the global drivers for the distribution of mycoheterotrophy for both the arbuscular and the ectomycorrhizal symbiosis from species occurrence data of these plants.

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