The far-reaching impact of wildfires extends beyond the charred landscapes, affecting even the tiniest inhabitants—microbes. Shedding light on how microbial communities evolve and adapt in the aftermath of a wildfire is pivotal in understanding the response of bacteria and fungi to significant environmental upheavals.
A recent study featured in mSystems highlights the pivotal role of dispersal, facilitated through mechanisms such as air and rain, in the succession of microbial populations following a destructive fire.
Researchers from the University of California, Irvine, embarked on a year-long investigation to monitor the resurgence of bacterial and fungal communities within the leaf litter of a burned field. Their findings unveiled a dynamic relationship between the changing seasons, plant regrowth, and the assembly of microbial communities, primarily driven by dispersal.
In recent decades, the frequency and magnitude of ecological disturbances like wildfires have witnessed a notable surge, attributed in part to climate change and human activities. Kristin Barbour, the lead author of the study and a Ph.D. student at the University of California, Irvine, emphasized the ecological significance of microorganisms, particularly those residing in surface soil. She noted, “Microbes, especially those in the surface soil, perform a number of really key ecosystem processes, like carbon and nitrogen cycling.” Bacteria and fungi are instrumental in decomposing dead and decaying plant matter within fields and forests.
Initially intending to explore microbial dispersal within the context of droughts, Barbour’s research direction shifted unexpectedly when an unanticipated wildfire swept through a field site near Irvine, known as Loma Ridge. What might have appeared as an impediment turned into a valuable opportunity. Barbour explained, “We wanted to take advantage of this disturbance, especially since wildfire is becoming more frequent in many parts of the world.”
The intense heat generated during a wildfire significantly alters the chemical composition of leaf litter, the habitat for many microbes, thereby reshaping the microbial communities within the ecosystem.
The study examined two distinct ecosystems impacted by the wildfire: a semi-arid grassland and a coastal sage scrub. To investigate microbial movement, researchers employed four configurations of dispersal bags. The first configuration utilized burned leaf litter to fill porous pouches, enabling microbes to move freely. The second, a control group, sealed leaf litter within impermeable bags to restrict movement. The third configuration featured porous bags with glass slides to collect microbes as they traversed, while the fourth configuration, another control group, employed sealed bags with glass slides.
Over the course of a year following the fire, Barbour and her colleagues retrieved dispersal bags from both sites and identified bacteria and fungi residing on the leaf litter. Their observations revealed varying effects of dispersal in the two environments, underscoring the environment-dependent nature of microbial responses. Barbour noted, “Which hurts our ability to make generalized statements.”
Nonetheless, some consistent patterns emerged. Overall, aerial dispersal played a dominant role in introducing microbes to the soil surface—accounting for 34% of bacteria and 42% of fungi. Additionally, during the initial months after the fire, before plant regrowth, the bulk soil (located beneath the leaf litter) explained a substantial proportion of immigrating bacteria.
Barbour highlighted that the study of microbial movement within the environment is an evolving area of research, intimately interconnected with broader issues concerning how significant disturbances reshape ecosystems. She expressed, “There’s a lot of exciting work being done right now, looking at dispersal and at microbial communities out in the environment.”