USING MICROFLUIDIC SOIL CHIPS TO EXAMINE THE EFFECTS OF DAILY AND WEEKLY FREEZE-THAW CYCLES ON FUNGAL AND BACTERIAL ACTIVITY IN ARCTIC SOILS AND THE FUNGAL MODEL SPECIES Coprinopsis cinerea

Abstract

Soil temperature fluctuations are typical at high latitudes in early spring or late autumn. Freeze-thaw cycles (FTCs) occur when the soil temperature fluctuates around 0°C, causing a change in the state of the soil solution. Due to climate change, FTCs are predicted to become more frequent and intense, especially in the Arctic, Antarctic, and cold temperate regions. In this study, two experiments were conducted using different designs of microfluidic soil chips to describe and determine the effects of daily FTCs on the fungal model species Coprinopsis cinerea, and the influence of daily and weekly FTCs on fungal and bacterial activity in Arctic soils. In addition, the effect of spatial complexity in the microfluidic chips on microbial communities was assessed. The results indicate that FTCs can cause significant bacterial and hyphal abundance differences. The bacterial density and the number of clusters decreased significantly in chips with weekly FTCs compared to daily FTCs. In addition, the number of hyphae inside the chips was reduced considerably under all FTCs treatments compared to the control. On the other hand, the different levels of spatial complexity within the chips showed no significant differences in bacterial activity between treatments, however the most complex fractal (fractal 6) reduced the presence of hyphae during the experiment compared to fractal 4. In summary, FTCs would cause changes in microbial activity and therefore affect soil biochemical properties and nutrient cycling. Thus, to assess potential changes in the ecological functions and services provided by ecosystems at high latitudes, it is crucial to understand how factors such as FTCs affect microbial communities.

Popular Abstract

Introduction

Soils on our planet provide humans with important ecosystem functions such as water filtration, food production, carbon, and nutrient cycling, but behind the scenes, soil-dwelling microorganisms play an important role in organic matter decomposition and nutrient cycling. Nonetheless, environmental conditions such as temperature, moisture, and soil pH affect their abundance and activity; for example, in cold environments, microbial activity slows down, contributing to carbon storage in soils.

However, the world is warming and experiencing the most extreme temperatures in decades. In the Arctic, warming temperatures are thinning the snow cover of soils. Once the snow layer is gone, the soil is exposed to large temperature fluctuations, creating new living conditions for the microorganisms that live there.

It was therefore important for me to study the effects of freeze-thaw cycles on two important groups of soil micro-organisms: Soil fungi and bacteria. To do this, I used a novel method involving transparent silicon microchips that can mimic the structures found in soil. In the first experiment, I used the model fungal species grey shag (Coprinopsis cinerea), which grows naturally in horse and cattle dung and fertilised straw; however, because of some interesting properties of this species, it is used by researchers to study fungal evolution, cell division, and other biological topics. For my second experiment, I used samples obtained from Arctic soils in Disko Island, Greenland.

My results

My first experiment showed that exposing the grey shag fungus to freeze-thaw cycles, with the lowest temperatures being -5°C and -20°C, reduced the growth of hyphae (filamentous structure of a fungus used to absorb nutrients, release enzymes, and other functions); and the hyphae were more affected by exposure to the lower temperatures (-20°C).

Regarding bacterial activity from Greenland Soils, the longest freeze-thaw cycles (thawing one day per week) reduced bacterial density compared to more frequent freeze-thaw cycles (thawing for a few hours each day). In addition, when bacteria formed clusters or gathered in groups, the longest freeze-thaw cycles also reduced the number of clusters inside the chips compared to treatments with more frequent freeze-thaw cycles.

A notable finding was the increase in bacterial density when hyphae were absent or when hyphal counts were lower and could be explained by competition for space, nutrients, production of secondary metabolites by bacteria or fungi, or a combination of these factors.


Conclusion

This study helps us understand the changes in soil microbial communities under the stronger and more frequent freeze-thaw cycles predicted by climate change in cold temperate regions, the Arctic and Antarctic. Microbes in soils have a major impact on carbon storage and nutrient cycling, so it is relevant to understand how climate change will affect ecosystem functions at high latitudes, and for conserving plant communities and other groups of soil-dwelling fauna.

• author: Gonzalez Oliveros, Yitsully Geraldine
• supervisor: Kristin Aleklett; Edith Hammer
• organization: Degree Projects in Biology
• course: BION02 20232
• year: 2024
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9185213
• date added to LUP: 2025-02-14 10:44:31
• date last changed: 2025-02-14 10:44:31