The effects of freeze thaw cycles on microbial communities in arctic soils and biocrusts
(2023) BION02 20212Degree Projects in Biology
- Abstract
- Rising global temperatures are creating a variety of changes in polar regions and pushing organisms to new extremes. Snow cover changes in the arctic are leading to exposed soils, allowing the soil to freeze at lower temperatures and experience freeze thaw cycles. In this study, I investigated the effect of freeze thaw cycles on arctic microorganisms, focusing on the main microbial groups bacteria, protists, and fungi. I also investigated the effect of soil pore structure on freezing and microbial dynamics, as small pore spaces can create a freezing point depression leading to unfrozen water. In this study I performed experiments on bulk soil samples and soil chips, which are an artificial soil system allowing us to study soil... (More)
- Rising global temperatures are creating a variety of changes in polar regions and pushing organisms to new extremes. Snow cover changes in the arctic are leading to exposed soils, allowing the soil to freeze at lower temperatures and experience freeze thaw cycles. In this study, I investigated the effect of freeze thaw cycles on arctic microorganisms, focusing on the main microbial groups bacteria, protists, and fungi. I also investigated the effect of soil pore structure on freezing and microbial dynamics, as small pore spaces can create a freezing point depression leading to unfrozen water. In this study I performed experiments on bulk soil samples and soil chips, which are an artificial soil system allowing us to study soil microorganisms in an environment of relevant scale to actual soil. I exposed soils and soil chips to freeze thaw cycles of different intensities and durations. I found that freeze thaw cycle frequency resulted in greater microbial mortality than compared to freezing temperature intensity, specifically when looking at bacteria and fungi. In the more frequent short term freeze thaw cycles, bacteria favored the smaller pore spaces. Using live freezing experiments, I was able to confirm that pockets of unfrozen water can remain in small pore spaces and may serve as a refuge for microorganisms in the event of freezing. I also found high microbial activity for long term -18℃, showing how well adapted arctic microorganisms are to surviving harsh winter conditions. (Less)
- Popular Abstract
- The effects of freeze thaw cycles on microbial communities in arctic soils and biocrusts
People are becoming more concerned about arctic soils and permafrost, as there are fears that with warming they may turn from a carbon sink to a carbon source, further exacerbating the effects of climate change. It is important to better understand what is happening within these soils especially at the microbial level, since soil microbes are drivers of these soil processes. One unexpected effect of rising temperatures is more intense freezing of soil due to snowmelt. Snow typically serves as an insulator, protecting the soil underneath from directly experiencing harsh weather conditions and freezing at extremely low temperatures. Exposed soil may... (More) - The effects of freeze thaw cycles on microbial communities in arctic soils and biocrusts
People are becoming more concerned about arctic soils and permafrost, as there are fears that with warming they may turn from a carbon sink to a carbon source, further exacerbating the effects of climate change. It is important to better understand what is happening within these soils especially at the microbial level, since soil microbes are drivers of these soil processes. One unexpected effect of rising temperatures is more intense freezing of soil due to snowmelt. Snow typically serves as an insulator, protecting the soil underneath from directly experiencing harsh weather conditions and freezing at extremely low temperatures. Exposed soil may also begin to experience freeze thaw cycles, where the soil temperature is frequently crossing the zero degree threshold. Freezing presents a challenge to soil microorganisms, affecting their ability to survive and reproduce. Soil is a complex environment, both spatially and chemically. Therefore, the effects of freezing will be different depending on where a microorganism is located in soil. For example, unfrozen water may remain in small pore spaces and ones with increased salts due to a freezing point depression.
In this study, I investigated how freezing affects soil microorganisms by looking at population changes of the main microbial groups: bacteria, protists, and fungi. I also investigated the effect of soil pore structure on freezing and soil microbes, focusing on two different sized pore spaces. For my experiment, I used a combination of microfluidic soil chips and bulk soil experiments on biocrust samples that were from Disko, Greenland and Latnjajaure, Sweden. Biocrusts are a layer of organisms, such as cyanobacteria, lichens, algae, and moss on the soil surface. These crusts serve a variety of functions such as preventing erosion and increasing biodiversity and nutrient availability in the soil. Soil chips are an artificial soil system made out of PDMS, which can be examined under a microscope. In these chips, soil microbes create similar population dynamics to what is experienced in actual soil. The bulk soil experiment I used is called leucine incorporation, which allows us to determine bacterial growth and how much bacteria is currently active in the soil.
I exposed the soils and soil chips to a control (+5℃ w/ light), mild freeze (-5℃), and deep freeze (-18℃). I had two groups of freezing treatments: long term freeze and short term freeze. Long term treatments were kept frozen for a period of a month, and then exposed to thaw in the phytotron (+5℃ w/ light) once a month. Short term treatments were kept frozen overnight in their respective treatments and then placed in the phytotron (+5℃ w/ light) during the day for a thaw period of eight hours. Later in the study, I exposed soil chips to live freezing under the microscope and focused on ice front development.
I found that for the soil chip experiments freezing frequency resulted in greater microbial mortality than compared to freezing temperature intensity, specifically when looking at bacteria and fungi. This was likely due to physical damage from the ice, rupturing the cell membranes of these organisms and causing them to die. Protists were less affected, due to adaptations that allow them to better survive freezing, such as a cyst form, changes to their membranes, and the secretion of antifreeze substances. The bulk soil experiments showed a contrasting result, with bacterial activity being similar for all freezing treatments apart from the control. Further investigating the soil chip bacteria data revealed that in the more frequent short term freeze thaw cycles, bacteria favored the smaller pore spaces. Using live freezing experiments, I was able to confirm that pockets of unfrozen water can remain in small pathways and may serve as a refuge for microorganisms in the event of freezing and recolonization of these chips was likely being done by bacteria that survived in these areas. Another interesting result of this study is the high microbial activity for long term -18℃, showing just how well adapted arctic microorganisms are to surviving harsh winter conditions. Even with being well adapted to freezing temperatures, the emergence of freeze thaw cycles will likely push the limits of arctic soil microorganisms to new extremes. Therefore, we should be aware of the effects that this will have on soil microbial communities, because they are the drivers of many processes that affect the soil ecosystem and beyond! (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9114009
- author
- Duljas, Julia
- supervisor
-
- Edith Hammer LU
- organization
- course
- BION02 20212
- year
- 2023
- type
- H2 - Master's Degree (Two Years)
- subject
- language
- English
- id
- 9114009
- date added to LUP
- 2023-05-05 11:00:18
- date last changed
- 2023-05-05 11:00:18
@misc{9114009,
abstract = {{Rising global temperatures are creating a variety of changes in polar regions and pushing organisms to new extremes. Snow cover changes in the arctic are leading to exposed soils, allowing the soil to freeze at lower temperatures and experience freeze thaw cycles. In this study, I investigated the effect of freeze thaw cycles on arctic microorganisms, focusing on the main microbial groups bacteria, protists, and fungi. I also investigated the effect of soil pore structure on freezing and microbial dynamics, as small pore spaces can create a freezing point depression leading to unfrozen water. In this study I performed experiments on bulk soil samples and soil chips, which are an artificial soil system allowing us to study soil microorganisms in an environment of relevant scale to actual soil. I exposed soils and soil chips to freeze thaw cycles of different intensities and durations. I found that freeze thaw cycle frequency resulted in greater microbial mortality than compared to freezing temperature intensity, specifically when looking at bacteria and fungi. In the more frequent short term freeze thaw cycles, bacteria favored the smaller pore spaces. Using live freezing experiments, I was able to confirm that pockets of unfrozen water can remain in small pore spaces and may serve as a refuge for microorganisms in the event of freezing. I also found high microbial activity for long term -18℃, showing how well adapted arctic microorganisms are to surviving harsh winter conditions.}},
author = {{Duljas, Julia}},
language = {{eng}},
note = {{Student Paper}},
title = {{The effects of freeze thaw cycles on microbial communities in arctic soils and biocrusts}},
year = {{2023}},
}