In this new post, Melissa Pastore—a global change ecologist and Postdoctoral Associate at the University of Vermont in the Rubenstein School of Environment and Natural Resources, USA, and with the Gund Institute for Environment, USA—discusses her recently published paper ‘Soil microbial legacies influence freeze–thaw responses of soil’. Her research takes a cross-scale approach to understanding the impacts of global environmental changes, spanning processes happening at the leaf and microbe levels to the functioning of whole ecosystems.

About the paper

Our paper investigates how the temperature regimes experienced by soil microbial communities in the past may influence their responses to changing winters as the climate warms. In temperate regions, like the northeastern USA, climate change is reducing the depth and duration of snow cover, which serves as an insulating blanket over soils. Therefore, perhaps ironically, warmer winters will make soils more susceptible to freezing. More frequent cycles of soil freezing and thawing may harm and disrupt communities of soil microbes which play a crucial role in ecosystem functioning. While we know a lot about how plants and wildlife are affected by climate change aboveground, the impacts happening belowground are still largely a mystery. Our study is one of a growing number which sheds light on winter season dynamics and the hidden world beneath our feet.

While it can be challenging to study underground phenomena and ecosystems can be complex, tools like microcosm experiments allow us to scale down and simplify systems to test specific mechanisms while controlling for environmental variability. Our team designed a microcosm experiment to uncover how legacies of past conditions influence soil microbial communities during freeze-thaw cycles. We trekked through the mountains of Vermont to collect soil samples, along with the microbial communities they harbor, and then used these samples to create a controlled microcosm experiment simulating freeze-thaw cycles. Our samples came from two forests that are similar in vegetation and soil type, but that have experienced different winter conditions. The colder site is at high elevation near the peak of Camel’s Hump, one of the highest mountains in Vermont, while the warmer site is nearby at low elevation. Our experimental setup allowed us to attribute any differences in freeze-thaw responses to the microbes, rather than the soil, and we investigated potential longer-term effects during a recovery period, making our study stand out from past research. In addition, we focused on a temperate ecosystem, whereas prior studies have mostly been done in polar and high alpine regions.

About the research

Our study is important because its shows that microbial communities may simultaneously exhibit vulnerabilities and resilience to freeze-thaw cycles, but to different degrees based on the past conditions they have experienced. Because microbes are responsible for many important functions in temperate forest ecosystems, the degree to which their activities are altered could impact forest health, water quality, greenhouse gas emissions, plant nutrient uptake, carbon stocks, and more.

I was surprised at how quickly both microbial communities recovered their activity following the repeated freeze-thaw cycles, raising questions about what thresholds may exist that could push them into a less readily reversed state when crossed. Is it the number of repeated freeze-thaw cycles? The duration? The intensity of the freeze? Other questions also remain, such as how climate legacies shape microbial responses in other systems and whether these effects scale to impact nutrient availability, water quality, and ecosystem carbon balances.

Every research project comes with challenges. Although we did not have any problems running the experiment, the trek up Camel’s Hump (normally an amazing hike!) in somewhat icy conditions was challenging because I had dropped something heavy on my foot the night before and my big toe was in bad shape (I’ll spare you the pictures). So it goes. Microbial respiration measurements can also be tricky and the timing had to be precise, but I had a great team that supported me through the early morning and late evening measurements, as well as a few surprise visits from a curious mouse that kept us on our toes.

About the author

I have always been drawn to the natural world, even before I knew what Ecology was. Growing up, my family regularly visited the shores of a barrier island on the east coast of the U.S. It was and remains a dreamlike place, but over the years I watched as it changed. I observed the shoreline recede and towering pines die with no new trees growing in their place, creating peculiar ghost forests. I wondered what was happening and why, and what it would mean for the mainland. The island was in constant motion, and as the coast changed, so did I.

I first became involved in ecological research as an undergraduate, exploring the links between above and belowground processes of temperate tree species. While my research has yet to circle back to the ghost forests (there’s still time!), I have investigated the effects of global changes on brackish marshes and grasslands and other types of forests, and I came to realize the interconnectedness of all living and non-living components of our world.

Now, as a Postdoctoral Associate at the University of Vermont, I continue to explore the impacts of human-caused global changes on ecosystems. Much of my current research focuses on cold spots across the mountainous New England landscape that may be buffered from macroscale climate change. I am investigating whether these areas are serving as microrefugia for tree species that are vulnerable to climate change, along with the ecosystem functions those species support, like carbon storage.

My advice to anyone getting into the field of Ecology is to be open and flexible. It is important to have a plan, both in the process of research and in pursuing a career, but often the path we end up taking is not the one we envisioned.

Enjoyed the blogpost and want to take a closer look at the hidden world of soil microbes and their response to changing winters? Click here!