Effects of reindeer grazing on the fungal community in subarctic mountain birch woodland and open tundra: implications for soil carbon storage
(2020) BIOM02 20201Degree Projects in Biology
- Abstract
- Due to a warming climate, tundra ecosystems are subject to shrub and treeline expansions which could lead to increased above- but decreased belowground carbon (C) stocks. An observed low soil C stock in some subarctic forests and tall shrublands has been suggested to be induced by priming of organic matter decomposition, possibly mediated by ectomycorrhizal fungi. On the other hand, the higher belowground C stocks in the open tundra could have resulted from the build-up of resistant mycelial necromass of ericoid mycorrhizal fungi residing below dwarf shrubs. It is known that the widespread reindeer grazing in the Arctic can also shape vegetation changes, yet its impact on the soil fungal community remains to be explored in depth. I... (More)
- Due to a warming climate, tundra ecosystems are subject to shrub and treeline expansions which could lead to increased above- but decreased belowground carbon (C) stocks. An observed low soil C stock in some subarctic forests and tall shrublands has been suggested to be induced by priming of organic matter decomposition, possibly mediated by ectomycorrhizal fungi. On the other hand, the higher belowground C stocks in the open tundra could have resulted from the build-up of resistant mycelial necromass of ericoid mycorrhizal fungi residing below dwarf shrubs. It is known that the widespread reindeer grazing in the Arctic can also shape vegetation changes, yet its impact on the soil fungal community remains to be explored in depth. I investigated the possible role of the root-associated fungal community in determining soil organic C (SOC) stocks under two different grazing regimes that presented alternative vegetation states. I measured SOC stocks and used high-throughput sequencing to determine relative abundances of fungal guilds under year-round grazing compared to non-summer grazing. While the belowground C stocks were similar across the two grazing regimes, I found that the soil fungal community differed depending on the grazing regime, although the root-associated fungi did not respond strongly. The results did not indicate any relationship between SOC stock and ectomycorrhizal fungi, suggesting that the dominating taxa present at the site are not causing net losses of soil C, or that the nutrient status of the soil played a role in modifying the response. In contrast, I found positive relationships between SOC stocks and root-associated ascomycetes, which propose a role for this fungal group in altering soil C storage. If management of reindeer grazing could be optimised to increase C stocks, for instance by favouring root-associated ascomycetes, it would be a valuable tool in the quest to mitigate positive climate feedbacks. (Less)
- Popular Abstract
- Reindeers and root-associated fungi: the real climate rebels?
Imagine a green and lush forest covering a previously open landscape that harbored only low statured vegetation. To the naked eye, this change might seem all good: A greater amount of carbon has been incorporated into plant biomass, and this carbon is taken directly from the atmosphere that otherwise has experienced a recent dramatic increase in CO2. However, belowground lurks a problem.
Below the vast open tundra of the north lies a great reservoir of carbon. While a warmer climate increases the plant growth aboveground, the carbon belowground is at risk of escaping into the atmosphere. A lower amount of carbon has been observed in the soil of subarctic forests and... (More) - Reindeers and root-associated fungi: the real climate rebels?
Imagine a green and lush forest covering a previously open landscape that harbored only low statured vegetation. To the naked eye, this change might seem all good: A greater amount of carbon has been incorporated into plant biomass, and this carbon is taken directly from the atmosphere that otherwise has experienced a recent dramatic increase in CO2. However, belowground lurks a problem.
Below the vast open tundra of the north lies a great reservoir of carbon. While a warmer climate increases the plant growth aboveground, the carbon belowground is at risk of escaping into the atmosphere. A lower amount of carbon has been observed in the soil of subarctic forests and shrublands compared to adjacent open tundra heath. This has been connected to a certain group of so called mycorrhizal fungi living in close connection to the tall shrub and tree roots. Common to all mycorrhizal fungi is that they search the soil for nutrients and transfers these to the plant host in return for energy in the form of carbon. In the productive tall shrub and forest ecosystems, a lot of carbon can be transferred to one type of fast growing mycorrhizal fungi, namely ectomycorrhizal fungi. They can then use this extra energy to decompose organic matter in the soil when scavenging for nutrients. At the same time they also release CO2 into the atmosphere. Certain kinds of ectomycorrhizal fungi are even masters of recycling their own biomass – or "eating themselves" – leaving little carbon to be returned to the soil, and potentially resulting in a net loss of carbon.
Reindeers and other root-associated fungi to the rescue?
Ericoid mycorrhizal fungi associate with the roots of dwarf shrubs growing in the open tundra. It was suggested that they aid the storage of soil carbon, due to the build-up of their dead biomass. Moreover, reindeers are the most common grazers of the tundra and have the potential to restrict tall shrub and tree growth, in some cases even favoring dwarf shrubs. If herbivory can alter vegetation communities, can it also impact the root-associated fungal community and ultimately change carbon storage? I investigated this question by collecting soil under different reindeer grazing regimes that also presented different vegetation states: woodland vs. open tundra. From the soil samples, I measured carbon content and identified the fungal community with DNA-sequencing. I found similar carbon storage across the two grazing regimes but the fungal community differed, although the response of the root-associated fungi was not very strong. When investigating relationships between soil carbon and ecto-mycorrhizal fungi, I did not find the expected negative connection. This was likely due to the fact that the dominating type of ectomycorrhizal species at the site were not the ones proposed to be involved in carbon losses. Further, as reindeers can increase nutrient availability through urine and excrements, it might have dampened the nutrient scavenging behavior of the ectomycorrhizal fungi - as the plants can just pick up these "cheap" nutrients from the soil thus paying less carbon to the soil fungi. On the other hand, I found positive relationships between soil carbon and so called root-associated ascomycetes (containing ericoid mycorrhizal fungi), which proposes a role for this fungal group in increasing carbon storage. Could reindeer grazing be managed to favour a root-associated fungal community that increases soil carbon storage in the long term? This question remains to be answered, but the results presented here give hints and provides increased understanding of ecological processes that can be used in the quest to mitigate positive climate feedbacks.
Master’s Degree Project in Biology with specialization in Ecology 30 credits, 2020
Department of Biology, Lund University
Supervisors: Henni Ylänne, Centre for Environmental and Climate Research, Lund University.
Carles Castaño, Department of Forest Mycology and Plant Pathology, Swedish University of Agricultural Sciences (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9022066
- author
- Madsen, Rieke Lo
- supervisor
- organization
- course
- BIOM02 20201
- year
- 2020
- type
- H2 - Master's Degree (Two Years)
- subject
- language
- English
- id
- 9022066
- date added to LUP
- 2020-06-24 13:11:50
- date last changed
- 2020-12-09 12:22:36
@misc{9022066,
abstract = {{Due to a warming climate, tundra ecosystems are subject to shrub and treeline expansions which could lead to increased above- but decreased belowground carbon (C) stocks. An observed low soil C stock in some subarctic forests and tall shrublands has been suggested to be induced by priming of organic matter decomposition, possibly mediated by ectomycorrhizal fungi. On the other hand, the higher belowground C stocks in the open tundra could have resulted from the build-up of resistant mycelial necromass of ericoid mycorrhizal fungi residing below dwarf shrubs. It is known that the widespread reindeer grazing in the Arctic can also shape vegetation changes, yet its impact on the soil fungal community remains to be explored in depth. I investigated the possible role of the root-associated fungal community in determining soil organic C (SOC) stocks under two different grazing regimes that presented alternative vegetation states. I measured SOC stocks and used high-throughput sequencing to determine relative abundances of fungal guilds under year-round grazing compared to non-summer grazing. While the belowground C stocks were similar across the two grazing regimes, I found that the soil fungal community differed depending on the grazing regime, although the root-associated fungi did not respond strongly. The results did not indicate any relationship between SOC stock and ectomycorrhizal fungi, suggesting that the dominating taxa present at the site are not causing net losses of soil C, or that the nutrient status of the soil played a role in modifying the response. In contrast, I found positive relationships between SOC stocks and root-associated ascomycetes, which propose a role for this fungal group in altering soil C storage. If management of reindeer grazing could be optimised to increase C stocks, for instance by favouring root-associated ascomycetes, it would be a valuable tool in the quest to mitigate positive climate feedbacks.}},
author = {{Madsen, Rieke Lo}},
language = {{eng}},
note = {{Student Paper}},
title = {{Effects of reindeer grazing on the fungal community in subarctic mountain birch woodland and open tundra: implications for soil carbon storage}},
year = {{2020}},
}