EVOLUTION OF ECTOMYCORRHIZA IN JUGLANDACEAE AND THE INFLUENCE OF THIS KEYSTONE SYMBIOSIS ON SOIL NITROGEN AVAILABILITY AND CARBON STORAGE IN TROPICAL FORESTS

Mycorrhizas are the most widespread fungal mutualism and are found on the roots of most vascular plants on earth. There are two main mycorrhizal types: arbuscular mycorrhizas and ectomycorrhizas. In tropical forests most tree species form arbuscular mycorrhizas, but ectomycorrhizal associations are also widespread. Although the mycorrhiza type has a major impact on tree community structure, the mycorrhizal status and ecology of many plant lineages has not been studied. The Juglandaceae (walnut family) is an ecologically and economically important lineage of trees distributed in temperate and tropical montane forests in Southeast Asia and the Americas.  At least 4 genera of Juglandaceae form associations with diverse EM fungi but 5 other genera remain unsampled. Anecdotal evidence suggests that the Juglans lineage may have lost the ability to form EM, making Juglandaceae an interesting family for studies of mycorrhizal ecology and testing hypotheses about mycorrhizal evolution. Recent studies of the EM tree Oreomunnea mexicana (Juglandaceae) indicate that this species dominates some montane forests and is symbiotically associated with a unique community of EM fungi. The soils with O. mexicana also have lower inorganic N and more organic matter than adjacent AM-dominated forest. Because O. mexicana and other tropical EM-forming Juglandaceae can be locally abundant, they may strongly impact soil nutrient cycles. However, the influence of O. mexicana and other Juglandaceae on nutrients is likely context-dependent and factors such as soil fertility, precipitation, temperature, and fungal community composition may all be important. Fine-root morphology and mycorrhiza type are key functional traits that influence nutrient uptake, ecosystem processes, seedling recruitment, and responses of plants to global change. Because montane tropical forests are under increasing anthropogenic pressure and are forecast to experience massive impacts due to climate change, it is critical that we study how these changes will impact the EM fungal communities with EM Juglandaceae and understand the role of both plants and fungi in nutrient cycling.
Here I propose to study EM associations of the tropical Juglandaceae and their influence on soil nutrient cycling and simultaneously study the evolution of the mycorrhizal symbiosis in Juglandacae. I expect to document the EM symbiosis in many Juglandacae species where this symbiosis was not previously known and also to document a putative loss of the EM symbiosis in the Juglans lineage. I also anticipate that the EM Juglandacae will have strong local effects on nutrient cycling in tropical forests across both Asia and the Americas. Given that EM associations of most Juglandaceae have not been studied, I also expect to discover endemic yet diverse EM fungal communities with many undescribed fungal taxa. For my postdoctoral mentor I have selected Assistant Professor Matthew Smith from the UF Department of Plant Pathology. Dr. Smith is recognized expert in ectomycorrhizal fungi and has ongoing international projects on ectomycorrhizal ecology and fungal evolution. Dr. Smith is an ideal collaborator for my fellowship and he has agreed to support my research in his lab and act as my postdoctoral mentor. In addition, I will be involved in collaboration with the Soltis Lab to resolve the phylogeny of Juglandaceae based on representative taxa using sequences of the entire chloroplast genomes and other available plastome sequences of Juglandaceae.