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Tian M, Salmon Y, Lintunen A, Oren R, Hölttä T. Seasonal dynamics and punctuated carbon sink reduction suggest photosynthetic capacity of boreal silver birch is reduced by the accumulation of hexose. THE NEW PHYTOLOGIST 2024. [PMID: 38853424 DOI: 10.1111/nph.19883] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2024] [Accepted: 05/15/2024] [Indexed: 06/11/2024]
Abstract
The 'assimilates inhibition hypothesis' posits that accumulation of nonstructural carbohydrates (NSCs) in leaves reduces leaf net photosynthetic rate, thus internally regulating photosynthesis. Experimental work provides equivocal support mostly under controlled conditions without identifying a particular NSC as involved in the regulation. We combined 3-yr in situ leaf gas exchange observations (natural dynamics) in the upper crown of mature Betula pendula simultaneously with measurements of concentrations of sucrose, hexoses (glucose and fructose), and starch, and similar measurements during several one-day shoot girdling (perturbation dynamics). Leaf water potential and water and nitrogen content were measured to account for their possible contribution to photosynthesis regulation. Leaf photosynthetic capacity (A/Ci) was temporally negatively correlated with NSC accumulation under both natural and perturbation states. For developed leaves, leaf hexose concentration explained A/Ci variation better than environmental variables (temperature history and daylength); the opposite was observed for developing leaves. The weaker correlations between NSCs and A/Ci in developing leaves may reflect their strong internal sink strength for carbohydrates. By contrast, the strong decline in photosynthetic capacity with NSCs accumulation in mature leaves, observed most clearly with hexose, and even more tightly with its constituents, provides support for the role of assimilates in regulating photosynthesis under natural conditions.
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Affiliation(s)
- Manqing Tian
- Department of Forest Sciences, Faculty of Agriculture and Forestry, University of Helsinki, PO Box 27, Helsinki, 00014, Finland
| | - Yann Salmon
- Department of Forest Sciences, Faculty of Agriculture and Forestry, University of Helsinki, PO Box 27, Helsinki, 00014, Finland
- Institute for Atmospheric and Earth System Research, Faculty of Science, University of Helsinki, PO Box 64, Helsinki, 00014, Finland
| | - Anna Lintunen
- Department of Forest Sciences, Faculty of Agriculture and Forestry, University of Helsinki, PO Box 27, Helsinki, 00014, Finland
- Institute for Atmospheric and Earth System Research, Faculty of Science, University of Helsinki, PO Box 64, Helsinki, 00014, Finland
| | - Ram Oren
- Department of Forest Sciences, Faculty of Agriculture and Forestry, University of Helsinki, PO Box 27, Helsinki, 00014, Finland
- Nicholas School of the Environment and Pratt School of Engineering, Duke University, Durham, NC, 27708, USA
| | - Teemu Hölttä
- Department of Forest Sciences, Faculty of Agriculture and Forestry, University of Helsinki, PO Box 27, Helsinki, 00014, Finland
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Hart AT, Landhäusser SM, Wiley E. Tracing carbon and nitrogen reserve remobilization during spring leaf flush and growth following defoliation. TREE PHYSIOLOGY 2024:tpae015. [PMID: 38281259 DOI: 10.1093/treephys/tpae015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2024]
Abstract
Woody plants rely on the remobilization of carbon (C) and nitrogen (N) reserves to support growth and survival when resource demand exceeds supply at seasonally predictable times like spring leaf flush and following unpredictable disturbances like defoliation. However, we have a poor understanding of how reserves are regulated and whether distance between source and sink tissues affects remobilization. This leads to uncertainty about which reserves-and how much-are available to support plant functions like leaf growth. To better understand the source of remobilized reserves and constraints on their allocation, we created aspen saplings with organ-specific labeled reserves by using stable isotopes (13C,15N) and grafting unlabeled or labeled stems to labeled or unlabeled root stocks. We first determined which organs had imported root or stem-derived C and N reserves after spring leaf flush. We then further tested spatial and temporal variation in reserve remobilization and import by comparing 1) upper and lower canopy leaves, 2) early and late leaves, and 3) early flush and re-flush leaves after defoliation. During spring flush, remobilized root C and N reserves were preferentially allocated to sinks closer to the reserve source (i.e., lower vs upper canopy leaves). However, the reduced import of 13C in late versus early leaves indicates reliance on C reserves declined over time. Following defoliation, re-flush leaves imported the same proportion of root N as spring flush leaves, but they imported a lower proportion of root C. This lower import of reserve C suggests that, after defoliation, leaf re-flush rely more heavily on current photosynthate, which may explain the reduced leaf mass recovery of re-flush canopies (31% of initial leaf mass). The reduced reliance on reserves occurred even though roots retained significant starch concentrations (~5% dry wt), suggesting aspen prioritizes the maintenance of root reserves at the expense of fast canopy recovery.
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Affiliation(s)
- Ashley T Hart
- Department of Renewable Resources, University of Alberta, Edmonton, Alberta, Canada
| | - Simon M Landhäusser
- Department of Renewable Resources, University of Alberta, Edmonton, Alberta, Canada
| | - Erin Wiley
- Department of Biology, University of Central Arkansas, Conway, Arkansas, USA
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Potkay A, Feng X. Dynamically optimizing stomatal conductance for maximum turgor-driven growth over diel and seasonal cycles. AOB PLANTS 2023; 15:plad044. [PMID: 37899972 PMCID: PMC10601388 DOI: 10.1093/aobpla/plad044] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Accepted: 07/04/2023] [Indexed: 10/31/2023]
Abstract
Stomata have recently been theorized to have evolved strategies that maximize turgor-driven growth over plants' lifetimes, finding support through steady-state solutions in which gas exchange, carbohydrate storage and growth have all reached equilibrium. However, plants do not operate near steady state as plant responses and environmental forcings vary diurnally and seasonally. It remains unclear how gas exchange, carbohydrate storage and growth should be dynamically coordinated for stomata to maximize growth. We simulated the gas exchange, carbohydrate storage and growth that dynamically maximize growth diurnally and annually. Additionally, we test whether the growth-optimization hypothesis explains nocturnal stomatal opening, particularly through diel changes in temperature, carbohydrate storage and demand. Year-long dynamic simulations captured realistic diurnal and seasonal patterns in gas exchange as well as realistic seasonal patterns in carbohydrate storage and growth, improving upon unrealistic carbohydrate responses in steady-state simulations. Diurnal patterns of carbohydrate storage and growth in day-long simulations were hindered by faulty modelling assumptions of cyclic carbohydrate storage over an individual day and synchronization of the expansive and hardening phases of growth, respectively. The growth-optimization hypothesis cannot currently explain nocturnal stomatal opening unless employing corrective 'fitness factors' or reframing the theory in a probabilistic manner, in which stomata adopt an inaccurate statistical 'memory' of night-time temperature. The growth-optimization hypothesis suggests that diurnal and seasonal patterns of stomatal conductance are driven by a dynamic carbon-use strategy that seeks to maintain homeostasis of carbohydrate reserves.
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Affiliation(s)
- Aaron Potkay
- Department of Civil, Environmental, and Geo-Engineering, University of Minnesota, Twin Cities, 500 Pillsbury Drive S.E., Minneapolis, MN 55455, USA
- Saint Anthony Falls Laboratory, University of Minnesota, Twin Cities, 23rd Ave SE, Minneapolis, MN 55414, USA
| | - Xue Feng
- Department of Civil, Environmental, and Geo-Engineering, University of Minnesota, Twin Cities, 500 Pillsbury Drive S.E., Minneapolis, MN 55455, USA
- Saint Anthony Falls Laboratory, University of Minnesota, Twin Cities, 23rd Ave SE, Minneapolis, MN 55414, USA
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Fleurial K, Vaziriyeganeh M, Zwiazek JJ. Getting cold feet: tree productivity at the mercy of soil temperature. TREE PHYSIOLOGY 2022; 42:1695-1699. [PMID: 35796551 DOI: 10.1093/treephys/tpac077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2022] [Accepted: 06/06/2022] [Indexed: 06/15/2023]
Affiliation(s)
- Killian Fleurial
- Department of Renewable Resources, University of Alberta, 442 Earth Sciences Building, Edmonton T6G 2E3, Canada
| | - Maryamsadat Vaziriyeganeh
- Department of Renewable Resources, University of Alberta, 442 Earth Sciences Building, Edmonton T6G 2E3, Canada
| | - Janusz J Zwiazek
- Department of Renewable Resources, University of Alberta, 442 Earth Sciences Building, Edmonton T6G 2E3, Canada
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Du Y, Lu R, Sun H, Cui E, Yan L, Xia J. Plant photosynthetic overcompensation under nocturnal warming: lack of evidence in subtropical evergreen trees. ANNALS OF BOTANY 2022; 130:109-119. [PMID: 35690359 PMCID: PMC9295921 DOI: 10.1093/aob/mcac075] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2022] [Accepted: 06/09/2022] [Indexed: 06/13/2023]
Abstract
BACKGROUND AND AIMS Increased plant photosynthesis under nocturnal warming is a negative feedback mechanism to overcompensate for night-time carbon loss to mitigate climate warming. This photosynthetic overcompensation effect has been observed in dry deciduous ecosystems but whether it exists in subtropical wet forest trees is unclear. METHODS Two subtropical evergreen tree species (Schima superba and Castanopsis sclerophylla) were grown in a greenhouse and exposed to ambient and elevated night-time temperature. The occurrence of the photosynthetic overcompensation effect was determined by measuring daytime and night-time leaf gas exchange and non-structural carbohydrate (NSC) concentration. KEY RESULTS A reduction in leaf photosynthesis for both species and an absence of persistent photosynthetic overcompensation were observed. The photosynthetic overcompensation effect was transient in S. superba due to respiratory acclimation and stomatal limitation. For S. superba, nocturnal warming resulted in insufficient changes in night-time respiration and NSC concentration to stimulate overcompensation and inhibited leaf stomatal conductance by increasing the leaf-to-air vapour pressure deficit. CONCLUSIONS The results indicate that leaf stomatal conductance is important for the photosynthetic overcompensation effect in different tree species. The photosynthetic overcompensation effect under nocturnal warming may be a transient occurrence rather than a persistent mechanism in subtropical forest ecosystems.
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Affiliation(s)
- Ying Du
- Zhejiang Tiantong Forest Ecosystem National Observation and Research Station, School of Ecological and Environmental Sciences, East China Normal University, Shanghai 200241, China
| | - Ruiling Lu
- Zhejiang Tiantong Forest Ecosystem National Observation and Research Station, School of Ecological and Environmental Sciences, East China Normal University, Shanghai 200241, China
| | - Huanfa Sun
- Zhejiang Tiantong Forest Ecosystem National Observation and Research Station, School of Ecological and Environmental Sciences, East China Normal University, Shanghai 200241, China
| | - Erqian Cui
- Zhejiang Tiantong Forest Ecosystem National Observation and Research Station, School of Ecological and Environmental Sciences, East China Normal University, Shanghai 200241, China
| | - Liming Yan
- Zhejiang Tiantong Forest Ecosystem National Observation and Research Station, School of Ecological and Environmental Sciences, East China Normal University, Shanghai 200241, China
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