OOS 41-3 - Effects of pulse fire disturbance, fire legacy, and their interaction on soil microbiomes' functional gene expression and native plant-microbiome interactions

Fire plays a major role in structuring plant communities across the globe, and the effects of fire are expected to keep increasing due to anthropogenic climate change,. Some of the most fire-prone regions of the USA, for instance, are projected to experience a 200–400% increase in burned area with the next 1°C increase in temperature resulting in substantial consequences for plant communities. Despite the reality that plant health and stress responses often depend on their interactions with microbial communities, the role of microbiomes in shaping plant community assembly post-fire is largely unclear. Here we present the first factorial manipulation of both fire and soil microbiome presence to investigate their interactive effects on plant performance across a suite of plant species with varying life history traits. We conducted fully factorial experiments on 11 species from the Florida scrub ecosystem to test plant performance responses to soils with varying fire histories (36 soil sources), the presence/absence of a microbiome, and exposure to an experimental burn. We found that while fire legacy did not significantly impact the fungal or bacterial communities, pulse fire from the prescribed burn did significantly restructure bacterial communities and alter the relative abundance of key fungal taxa. Some of the most striking shifts occurred among the fungal taxa Talaromyces diversus (P-solubilizing fungal species and pathogen antagonist), which had the greatest decreases after fire, and Gibberella fujikuroi (a virulent plant pathogen), which had the greatest increase after fire. Our plant experiments revealed interactive ‘pulse’ effects between fire and the soil microbiome on plant performance. On average, post-fire soil microbiomes strongly reduced plant productivity compared to unburned or sterilized soils. Interestingly, longer-term fire ‘legacy’ effects had minor impacts on plant performance and were unrelated to soil microbiomes. While pulse fire effects on plant–microbiome interactions were shorter-term, they could have long-term consequences for plant communities by establishing differential microbiome-mediated priority effects during post-disturbance succession. The prominence of pulse fire effects on plant–microbe interactions has even greater import due to expected increases in fire disturbances resulting from climate change. To gain insight into what functional changes in the microbiome may be impacting plants post-fire, we are currently complementing this study with a meta-transcriptomic analysis of the microbiome from these same soils, which have experienced both pulse fire treatments and different fire legacies.