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Joannie Beaulne
Université du Québec à Montréal
Corresponding Author
ORCiD: https://orcid.org/0000-0002-5889-6757
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Background: Black spruce (Picea mariana (Mill.) BSP)-forested peatlands are widespread ecosystems in boreal North America in which peat accumulation, known as the paludification process, has been shown to induce forest growth decline. However, the ecophysiological mechanisms that lead to growth reductions in black spruce remain unexplored. Trees growing in paludified forests have to deal with continuously evolving environmental conditions (e.g., water table rise, increasing peat thickness) that may require growth mechanism adjustments over time. In this study, we investigated tree ecophysiological mechanisms along a paludification gradient in a boreal forested peatland of eastern Canada by combining peat-based and tree-ring analyses. Carbon and oxygen stable isotopes in tree rings were used to document changes in carbon assimilation rates, stomatal conductance, and water use efficiency. In addition, paleohydrological analyses were performed to evaluate the dynamical ecophysiological adjustments of black spruce trees to site-specific water table variations.
Results: Increasing peat accumulation considerably impacted forest growth, but no significant differences in tree water use efficiency (iWUE) were observed between the study sites. Tree-ring isotopic analysis indicates no iWUE decrease over the last 100 years, but rather an important increase at each site up to the 1980s, before iWUE stabilized. Surprisingly, inferred basal area increments did not reflect such trends. Our results suggest that the slower growth rates observed at the most paludified sites are attributable, at least partially, to both lower carbon assimilation rates and stomatal conductance. These findings show that iWUE variations do not necessarily reflect tree ecophysiological adjustments required by changes in growing conditions. Local water table variations induced no changes in ecophysiological mechanisms, but the synchronous shift in iWUE observed at all sites in the mid-1980s suggests a tree response to regional or global factors, such as increasing atmospheric CO2 concentration.
Conclusions: Our study shows that paludification induces black spruce growth decline without, however, altering tree water use efficiency in boreal forested peatlands. This is the first attempt in exploring the complex interactions between stem growth, ecophysiological mechanisms, and environmental conditions in paludified sites. Additional research on carbon allocation strategies is of utmost importance to understand the carbon sink capacity of these widespread ecosystems and better predict their response to future climate change.
Keywords
black spruce growth, boreal biome, carbon allocation, ecophysiological mechanisms, forested peatland, paludification, stable isotope, water use efficiency
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CURRENT STATUS: Under Review
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Posted 14 Jan, 2021
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Editorial decision: Minor Revision
On 24 Jan, 2021
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Received 20 Jan, 2021
Review #2 received
Received 17 Jan, 2021
Reviewer #2 agreed
On 10 Jan, 2021
Reviewers invited
Invitations sent on 09 Jan, 2021
Reviewer #1 agreed
On 09 Jan, 2021
Editor assigned
On 04 Jan, 2021
Submission checks complete
On 04 Jan, 2021
Editor invited
On 04 Jan, 2021
No comments provided
Editorial decision: Major Revision
On 18 Oct, 2020
Review #2 received
Received 15 Oct, 2020
Review #1 received
Received 20 Sep, 2020
Reviewer #2 agreed
On 10 Sep, 2020
Reviewer #1 agreed
On 09 Sep, 2020
Reviewers invited
Invitations sent on 18 Aug, 2020
Editor assigned
On 11 Aug, 2020
First submitted
On 10 Aug, 2020
Submission checks complete
On 10 Aug, 2020
Editor invited
On 10 Aug, 2020
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Subject Areas
Forestry
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This preprint is under consideration at Forest Ecosystems. A preprint is a preliminary version of a manuscript that has not completed peer review at a journal. Research Square does not conduct peer review prior to posting preprints. The posting of a preprint on this server should not be interpreted as an endorsement of its validity or suitability for dissemination as established information or for guiding clinical practice.
Learn more about In Review
Research
Joannie Beaulne
Université du Québec à Montréal
Corresponding Author
ORCiD: https://orcid.org/0000-0002-5889-6757
Badges
Prescreen
This manuscript passed our Prescreen assessment
Complete author information
Appropriate declaration statements
Potential risks to human health
Prescreen
Peer Review Timeline
CURRENT STATUS: Under Review
Version 2
Posted 14 Jan, 2021
No community comments so far
Editorial decision: Minor Revision
On 24 Jan, 2021
Review #1 received
Received 20 Jan, 2021
Review #2 received
Received 17 Jan, 2021
Reviewer #2 agreed
On 10 Jan, 2021
Reviewers invited
Invitations sent on 09 Jan, 2021
Reviewer #1 agreed
On 09 Jan, 2021
Editor assigned
On 04 Jan, 2021
Submission checks complete
On 04 Jan, 2021
Editor invited
On 04 Jan, 2021
No comments provided
Editorial decision: Major Revision
On 18 Oct, 2020
Review #2 received
Received 15 Oct, 2020
Review #1 received
Received 20 Sep, 2020
Reviewer #2 agreed
On 10 Sep, 2020
Reviewer #1 agreed
On 09 Sep, 2020
Reviewers invited
Invitations sent on 18 Aug, 2020
Editor assigned
On 11 Aug, 2020
First submitted
On 10 Aug, 2020
Submission checks complete
On 10 Aug, 2020
Editor invited
On 10 Aug, 2020
Metrics
Comments: 0
PDF Downloads: ...
HTML Views: ...
Subject Areas
Forestry
License:
This work is licensed under a CC BY 4.0 License. Read Full License
Background: Black spruce (Picea mariana (Mill.) BSP)-forested peatlands are widespread ecosystems in boreal North America in which peat accumulation, known as the paludification process, has been shown to induce forest growth decline. However, the ecophysiological mechanisms that lead to growth reductions in black spruce remain unexplored. Trees growing in paludified forests have to deal with continuously evolving environmental conditions (e.g., water table rise, increasing peat thickness) that may require growth mechanism adjustments over time. In this study, we investigated tree ecophysiological mechanisms along a paludification gradient in a boreal forested peatland of eastern Canada by combining peat-based and tree-ring analyses. Carbon and oxygen stable isotopes in tree rings were used to document changes in carbon assimilation rates, stomatal conductance, and water use efficiency. In addition, paleohydrological analyses were performed to evaluate the dynamical ecophysiological adjustments of black spruce trees to site-specific water table variations.
Results: Increasing peat accumulation considerably impacted forest growth, but no significant differences in tree water use efficiency (iWUE) were observed between the study sites. Tree-ring isotopic analysis indicates no iWUE decrease over the last 100 years, but rather an important increase at each site up to the 1980s, before iWUE stabilized. Surprisingly, inferred basal area increments did not reflect such trends. Our results suggest that the slower growth rates observed at the most paludified sites are attributable, at least partially, to both lower carbon assimilation rates and stomatal conductance. These findings show that iWUE variations do not necessarily reflect tree ecophysiological adjustments required by changes in growing conditions. Local water table variations induced no changes in ecophysiological mechanisms, but the synchronous shift in iWUE observed at all sites in the mid-1980s suggests a tree response to regional or global factors, such as increasing atmospheric CO2 concentration.
Conclusions: Our study shows that paludification induces black spruce growth decline without, however, altering tree water use efficiency in boreal forested peatlands. This is the first attempt in exploring the complex interactions between stem growth, ecophysiological mechanisms, and environmental conditions in paludified sites. Additional research on carbon allocation strategies is of utmost importance to understand the carbon sink capacity of these widespread ecosystems and better predict their response to future climate change.
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
The full text of this article is available to read as a PDF.
This is a list of supplementary files associated with this preprint. Click to download.
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