Mycorrhizas as mediators of plant population dynamics and community assembly

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Mycorrhizal fungi form symbiotic associations with plants, providing nutrients and pathogen protection in exchange for plant-derived carbon. As such, mycorrhizas can regulate plant population dynamics through changes in plant growth and by modifying how soil biota affect the recruitment of conspecific seedlings (plant-soil feedbacks; PSFs). These effects can cascade across plant communities, influencing their structure and function. However, mycorrhizal growth responses and PSFs are also highly context dependent, and despite their importance, we lack a predictive framework for their effects on plant communities. Plant traits are increasingly being used to understand plant community assembly, and are often correlated with mycorrhizal responses and PSFs. As such, they could be used to improve our understanding of, and ability to predict, mycorrhizal effects on plant communities. My research program focuses on developing predictive models of mycorrhizal responses and PSFs using plant traits, and integrating these models into larger trait-based models of invasion and community dynamics. My short-term objectives are to 1) identify the mechanisms by which mycorrhizas alter plant community assembly, and 2) to quantify the influence of mycorrhizas on the temporal dynamics of PSFs. To determine mycorrhiza effects on community assembly, I will experimentally manipulate the composition of plants and fungi along a water gradient. By developing niche and trait based models of plant and fungal community assembly, I can quantify mycorrhiza effects on community assembly and covariation between plant and fungal communities. To explore the temporal dynamics of PSF, I will use two systems where population age is estimable: invasion in grasslands and forest regeneration. In both systems, I will measure PSF among different age-classes for species differing in mycorrhizal dependency (grasslands) or mycorrhizal type (forests). In grasslands, these data will be combined with field surveys and competition experiments to determine how PSF alters invasion impacts over time. In forests, they will be combined with field surveys of seedlings to test whether PSF drives temporal shifts in conspecific distance dependence, and with multi-taxon next generation sequencing to identify the soil biota driving these changes. The proposed research has the potential to impact both applied and fundamental ecology. By quantifying how invasion impacts change over time, this research will aid the development of management and restoration plans for these invaders. Additionally, quantifying age dependent recruitment in forests can help optimize harvest times to maximize stand replacement. More broadly, mechanistically linking plant traits to mycorrhiza effects on plant populations and communities lays the groundwork for predictive models of plant community assembly a primary goal in community ecology.