Photosynthetic and Respiratory Responses of Two Bog Shrub Species to Whole Ecosystem Warming and Elevated CO2 at the Boreal-Temperate Ecotone

Eric J. Ward; Jeffrey M. Warren; David A. McLennan; Mirindi E. Dusenge; Danielle A. Way; Stan D. Wullschleger; Paul J. Hanson

doi:10.3389/ffgc.2019.00054

Photosynthetic and Respiratory Responses of Two Bog Shrub Species to Whole Ecosystem Warming and Elevated CO₂ at the Boreal-Temperate Ecotone

Eric J. Ward, Jeffrey M. Warren, David A. McLennan, Mirindi E. Dusenge, Danielle A. Way, Stan D. Wullschleger, Paul J. Hanson

Research output: Contribution to journal › Article › peer-review

10 Scopus citations

Abstract

Peatlands within the boreal-temperate ecotone contain the majority of terrestrial carbon in this region, and there is concern over the fate of such carbon stores in the face of global environmental changes. The Spruce and Peatland Response Under Changing Environments (SPRUCE) facility aims to advance the understanding of how such peatlands may respond to such changes, using a combination of whole ecosystem warming (WEW; +0, 2.25, 4.5, 6.75, and 9°C) and elevated CO₂ (eCO₂; +500 ppm) treatments in an intact bog ecosystem. We examined photosynthetic and respiration responses in leaves of two ericaceous shrub species–leatherleaf [Chamaedaphne calyculata (L.) Moench] and bog Labrador tea [Rhododendron groenlandicum (Oeder) Kron & Judd]–to the first year of combined eCO₂ and WEW treatments at SPRUCE. We surveyed the leaf N content per area (N_area), net photosynthesis (A_ST) and respiration (R_D25) at 25°C and 400 ppm CO₂ and net photosynthesis at mean growing conditions (A_GR) of newly emerged, mature and overwintered leaves. We also measured leaf non-structural carbohydrate content (NSC) in mature leaves. The effects of WEW and eCO₂ varied by season and species, highlighting the need to accommodate such variability in modeling this system. In mature leaves, we did not observe a response to either treatment of A_ST or R_D25 in R. groenlandicum, but we did observe a 50% decrease in A_ST of C. calyculata with eCO₂. In mature leaves under eCO₂, neither species had increased A_GR and both had increases in NSC, indicating acclimation of photosynthesis to eCO₂ may be related to source-sink imbalances of carbohydrates. Thus, productivity gains of shrubs under eCO₂ may be lower than previously predicted for this site by models not accounting for such acclimation. In newly emerged leaves, A_ST increased with WEW in R. groenlandicum, but not C. calyculata. Overwintered leaves exhibited a decrease in R_D25 for R. groenlandicum and in A_ST for C. calyculata with increasing WEW, as well as an increase of A_GR with eCO₂ in both species. Responses in newly emerged and overwintered leaves may reflect physiological acclimation or phenological changes in response to treatments.

Original language	English
Article number	54
Journal	Frontiers in Forests and Global Change
Volume	2
DOIs	https://doi.org/10.3389/ffgc.2019.00054
State	Published - Sep 12 2019

Bibliographical note

Publisher Copyright:
© Copyright © 2019 Ward, Warren, McLennan, Dusenge, Way, Wullschleger and Hanson.

Funding

Way, D. A., Oren, R., and Kroner, Y. (2015). The space-time continuum: the effects of elevated CO2 and temperature on trees and the importance of scaling. Plant Cell Environ. 38, 991–1007. doi: 10.1111/pce.12527 Way, D. A., and Oren, R. A. (2010). Differential responses to changes in growth temperature between trees from different functional groups and biomes: a review and synthesis of data. Tree Physiol. 30, 669–688. doi: 10.1093/treephys/tpq015 Way, D. A., and Yamori, W. (2014). Thermal acclimation of photosynthesis: on the importance of adjusting our definitions and accounting for thermal acclimation of respiration. Photosynth. Res. 119, 89–100. doi: 10.1007/s11120-013-9873-7 Weltzin, J. F., Pastor, J., Harth, C., Bridgham, S. D., Updegraff, K., and Chapin, C. T. (2000). Response of bog and fen plant communities to warming and water-table manipulations. Ecology 81, 3464–3478. doi: 10.1890/0012-9658(2000)081[3464:ROBAFP]2.0.CO;2 Woodruff, D. R., and Meinzer, F. C. (2011). Water stress, shoot growth and storage of non-structural carbohydrates along a tree height gradient in a tall conifer. Plant Cell Environ. 34, 1920–1930. doi: 10.1111/j.1365-3040.2011.02388.x Disclaimer: This manuscript has been co-authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the US Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy (DOE) will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan). We greatly appreciate field and laboratory support by Joanne Childs, Deanne Brice, and Robert Nettles. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research. ORNL is managed by UT-Battelle, LLC, for the DOE under contract DE-AC05-00OR22725. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Funders	Funder number
Deanne Brice
Joanne Childs
U.S. Government
U.S. Department of Energy	DE-AC05-00OR22725
Office of Science
Biological and Environmental Research
Oak Ridge National Laboratory
UT-Battelle

Keywords

Chamaedaphne calyculata
Rhododendron groenlandicum
elevated CO
ericaceous shrubs
gas exchange
non-structural carbohydrates
whole ecosystem warming

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10.3389/ffgc.2019.00054

Cite this

@article{f983b7fe312049f9848a0cb89f752fa8,

title = "Photosynthetic and Respiratory Responses of Two Bog Shrub Species to Whole Ecosystem Warming and Elevated CO2 at the Boreal-Temperate Ecotone",

abstract = "Peatlands within the boreal-temperate ecotone contain the majority of terrestrial carbon in this region, and there is concern over the fate of such carbon stores in the face of global environmental changes. The Spruce and Peatland Response Under Changing Environments (SPRUCE) facility aims to advance the understanding of how such peatlands may respond to such changes, using a combination of whole ecosystem warming (WEW; +0, 2.25, 4.5, 6.75, and 9°C) and elevated CO2 (eCO2; +500 ppm) treatments in an intact bog ecosystem. We examined photosynthetic and respiration responses in leaves of two ericaceous shrub species–leatherleaf [Chamaedaphne calyculata (L.) Moench] and bog Labrador tea [Rhododendron groenlandicum (Oeder) Kron & Judd]–to the first year of combined eCO2 and WEW treatments at SPRUCE. We surveyed the leaf N content per area (Narea), net photosynthesis (AST) and respiration (RD25) at 25°C and 400 ppm CO2 and net photosynthesis at mean growing conditions (AGR) of newly emerged, mature and overwintered leaves. We also measured leaf non-structural carbohydrate content (NSC) in mature leaves. The effects of WEW and eCO2 varied by season and species, highlighting the need to accommodate such variability in modeling this system. In mature leaves, we did not observe a response to either treatment of AST or RD25 in R. groenlandicum, but we did observe a 50% decrease in AST of C. calyculata with eCO2. In mature leaves under eCO2, neither species had increased AGR and both had increases in NSC, indicating acclimation of photosynthesis to eCO2 may be related to source-sink imbalances of carbohydrates. Thus, productivity gains of shrubs under eCO2 may be lower than previously predicted for this site by models not accounting for such acclimation. In newly emerged leaves, AST increased with WEW in R. groenlandicum, but not C. calyculata. Overwintered leaves exhibited a decrease in RD25 for R. groenlandicum and in AST for C. calyculata with increasing WEW, as well as an increase of AGR with eCO2 in both species. Responses in newly emerged and overwintered leaves may reflect physiological acclimation or phenological changes in response to treatments.",

keywords = "Chamaedaphne calyculata, Rhododendron groenlandicum, elevated CO, ericaceous shrubs, gas exchange, non-structural carbohydrates, whole ecosystem warming",

author = "Ward, {Eric J.} and Warren, {Jeffrey M.} and McLennan, {David A.} and Dusenge, {Mirindi E.} and Way, {Danielle A.} and Wullschleger, {Stan D.} and Hanson, {Paul J.}",

note = "Publisher Copyright: {\textcopyright} Copyright {\textcopyright} 2019 Ward, Warren, McLennan, Dusenge, Way, Wullschleger and Hanson.",

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month = sep,

day = "12",

doi = "10.3389/ffgc.2019.00054",

language = "English",

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TY - JOUR

T1 - Photosynthetic and Respiratory Responses of Two Bog Shrub Species to Whole Ecosystem Warming and Elevated CO2 at the Boreal-Temperate Ecotone

AU - Ward, Eric J.

AU - Warren, Jeffrey M.

AU - McLennan, David A.

AU - Dusenge, Mirindi E.

AU - Way, Danielle A.

AU - Wullschleger, Stan D.

AU - Hanson, Paul J.

PY - 2019/9/12

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N2 - Peatlands within the boreal-temperate ecotone contain the majority of terrestrial carbon in this region, and there is concern over the fate of such carbon stores in the face of global environmental changes. The Spruce and Peatland Response Under Changing Environments (SPRUCE) facility aims to advance the understanding of how such peatlands may respond to such changes, using a combination of whole ecosystem warming (WEW; +0, 2.25, 4.5, 6.75, and 9°C) and elevated CO2 (eCO2; +500 ppm) treatments in an intact bog ecosystem. We examined photosynthetic and respiration responses in leaves of two ericaceous shrub species–leatherleaf [Chamaedaphne calyculata (L.) Moench] and bog Labrador tea [Rhododendron groenlandicum (Oeder) Kron & Judd]–to the first year of combined eCO2 and WEW treatments at SPRUCE. We surveyed the leaf N content per area (Narea), net photosynthesis (AST) and respiration (RD25) at 25°C and 400 ppm CO2 and net photosynthesis at mean growing conditions (AGR) of newly emerged, mature and overwintered leaves. We also measured leaf non-structural carbohydrate content (NSC) in mature leaves. The effects of WEW and eCO2 varied by season and species, highlighting the need to accommodate such variability in modeling this system. In mature leaves, we did not observe a response to either treatment of AST or RD25 in R. groenlandicum, but we did observe a 50% decrease in AST of C. calyculata with eCO2. In mature leaves under eCO2, neither species had increased AGR and both had increases in NSC, indicating acclimation of photosynthesis to eCO2 may be related to source-sink imbalances of carbohydrates. Thus, productivity gains of shrubs under eCO2 may be lower than previously predicted for this site by models not accounting for such acclimation. In newly emerged leaves, AST increased with WEW in R. groenlandicum, but not C. calyculata. Overwintered leaves exhibited a decrease in RD25 for R. groenlandicum and in AST for C. calyculata with increasing WEW, as well as an increase of AGR with eCO2 in both species. Responses in newly emerged and overwintered leaves may reflect physiological acclimation or phenological changes in response to treatments.

AB - Peatlands within the boreal-temperate ecotone contain the majority of terrestrial carbon in this region, and there is concern over the fate of such carbon stores in the face of global environmental changes. The Spruce and Peatland Response Under Changing Environments (SPRUCE) facility aims to advance the understanding of how such peatlands may respond to such changes, using a combination of whole ecosystem warming (WEW; +0, 2.25, 4.5, 6.75, and 9°C) and elevated CO2 (eCO2; +500 ppm) treatments in an intact bog ecosystem. We examined photosynthetic and respiration responses in leaves of two ericaceous shrub species–leatherleaf [Chamaedaphne calyculata (L.) Moench] and bog Labrador tea [Rhododendron groenlandicum (Oeder) Kron & Judd]–to the first year of combined eCO2 and WEW treatments at SPRUCE. We surveyed the leaf N content per area (Narea), net photosynthesis (AST) and respiration (RD25) at 25°C and 400 ppm CO2 and net photosynthesis at mean growing conditions (AGR) of newly emerged, mature and overwintered leaves. We also measured leaf non-structural carbohydrate content (NSC) in mature leaves. The effects of WEW and eCO2 varied by season and species, highlighting the need to accommodate such variability in modeling this system. In mature leaves, we did not observe a response to either treatment of AST or RD25 in R. groenlandicum, but we did observe a 50% decrease in AST of C. calyculata with eCO2. In mature leaves under eCO2, neither species had increased AGR and both had increases in NSC, indicating acclimation of photosynthesis to eCO2 may be related to source-sink imbalances of carbohydrates. Thus, productivity gains of shrubs under eCO2 may be lower than previously predicted for this site by models not accounting for such acclimation. In newly emerged leaves, AST increased with WEW in R. groenlandicum, but not C. calyculata. Overwintered leaves exhibited a decrease in RD25 for R. groenlandicum and in AST for C. calyculata with increasing WEW, as well as an increase of AGR with eCO2 in both species. Responses in newly emerged and overwintered leaves may reflect physiological acclimation or phenological changes in response to treatments.

KW - Chamaedaphne calyculata

KW - Rhododendron groenlandicum

KW - elevated CO

KW - ericaceous shrubs

KW - gas exchange

KW - non-structural carbohydrates

KW - whole ecosystem warming

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DO - 10.3389/ffgc.2019.00054

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