How do biomes rebuild?

Hello and welcome to another installment of All things Bacteriology, where we talk about the latest and greatest happenings in the microbial world. In the past, I’ve mostly talked about what bacteria do to help human health, industrial manufacturing, and bioenergy. Before microbes were important for any of these uses though, microbes shaped the world we live in today.

Microbes were the origin of life in deep, hydrothermal vents on the ocean floor. Billions of years later, microbes oxygenated the atmosphere, rapidly accelerating evolution of other, more complex life forms and taming the once harsh and unforgiving crust of the earth. Microbes in the environment today continue the legacy of their ancestors, producing as much oxygen as the trees around the world. They cycle nutrients in the soil, breaking down dead and decaying organisms into fuel for new things to grow. Microbes’ ability to reshape our world is a tale as old as time, and now that we have the tools to study them in extreme detail, we can understand exactly how they work.

If microbes are so good at building environments, then it stands to reason they are relatively adept at rebuilding communities too. We’ve seen this before in the gut microbiome, where strong microbial communities can sometimes rebound after the decimation that follows antibiotic treatment. But what about more complex ecosystems where microbes aren’t the only life forms?

As forest fires become more common and powerful, a budding area of research is forest fire succession. How does a forest rebuild after a devastating wildfire? For larger plants, we know that there is an order of succession. Grasses and shrubs lead the way for larger bushes and trees. But what about the microbes? Soil microbes are es of any biome, as they cycle nutrients and enrich the soil. How do they come back?

In the past few years, researchers at UC Irvine have developed a model to study how microbes return to burned environments. To track this, they studied two different biomes: a more arid grassland and a coastal sage scrub biome shown below. They placed burned leaf litter that was devoid of any life forms in porous bags that let microbes in and left them in various parts of these two ecosystems. Over the course of a year, researchers gathered five samples from each field to study when bacteria returned to the leaf litter.

This study revealed several interesting results:

1. “The answer, my friends is blowing in the wind.” Wind and rain can actually transport microbes and bring them back into the environment. This allows these microbes to rejuvenate the soil and set the stage for larger plants to put down roots.
2. Microbial composition changes with environment. The composition of bacteria that returned to the soil was markedly different between the drier grassland or wetter coastal scrub.
3. Microbial composition of the soil changes by season. Even though the environment remains the same in recovery, which microbes appear over the course of a year changes by season. This makes sense given the fact that wind and rain, which can be seasonal weather patterns, predicate microbes landing into the soil.

Such research projects tend to focus on incredibly specific questions, and so it can sometimes be hard to see the forest for the trees when looking at results. Discovering the migration patterns of soil bacteria has very interesting implications. For one, understanding how to rejuvenate soil, which bacteria fit different biomes, and which season they arrive in can help us recover and rebuild faster after wildfires. This can also help dictate how we can help remediate our biomes to respond better to large-scale environmental perturbations, especially as they become more prevalent with each passing year.