Fire is a global phenomenon that annually burns approximately 3% of Earth’s terrestrial surface. While fire is an important component of many terrestrial ecosystems, climate change and anthropogenic influence are expected to alter global fire regimes (particularly fire frequency and intensity). This makes understanding fire’s role under a changing climate critical to preserving threatened ecosystems. Despite the need to protect these ecosystems, the manipulation of fire regimes is dangerous and often impossible in most systems. Pyrophilic, or fire recurrent ecosystems, however, may offer a useful model due to their long-term adaptation to recurrent fires. The fire regimes of pyrophilic ecosystems are maintained by feedbacks between fire and plant fuels, which has led to a historical focus on the role of plants in pyrophilic systems. This approach has largely ignored the role of soil microbes in these systems, despite their ability to modify plant fuel loads through saprotrophic, mutualistic, and pathogenic interactions. By improving our knowledge of the microbial processes that underly pyrophilic ecosystems, we may be able to better respond to future changes in the frequency and intensity of global fire regimes. In this dissertation, I assessed microbial roles in pyrophilic ecosystems by testing four primary questions 1) Does fire drive similar shifts to microbial community structure and seasonal trajectories across pyrophilic systems, 2-3) Do fire regime components (e.g. fire frequency and intensity) alter the microbial mediation of plant fuel loads via decomposition, and 4) Does fire modify microbial and abiotic soil components in ways that influence plant fuel production? I hypothesized that fire would modify microbial communities and their function (e.g. decomposition, mutualism, and pathogenic effects) in ways that modified plant fuel dynamics. I used four complementary experiments that manipulated fire regime components and combined molecular, field, and greenhouse techniques to develop a holistic understanding of microbial roles in pyrophilic ecosystems. Fire had similar effects on fungal community structure and seasonal trajectories across pyrophilic ecosystems. Furthermore, as the frequency and intensity of fires increased, microbial functions like decomposition slowed, and microbial interactions with plant fuel production were altered. This indicates that fire alters microbial community structure, seasonal dynamics, and function in ways that modify plant fuel loads. Since fire-microbial interactions influence plant fuel dynamics in ways that lead to fuel accumulation, this could drive positive feedbacks on future fires, and suggests that soil microbes play integral roles in maintaining the fire regimes of pyrophilic ecosystems. By understanding the processes that govern the fire regimes of pyrophilic ecosystems, we can better respond to and preserve terrestrial systems against future increases in fire frequency and intensity due to climate change and anthropogenic influence.
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