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  • 1. Drößler, Lars
    et al.
    Attocchi, G
    Jensen, Anna M.
    Occurrence and management of oak in southern Swedish forests2012In: Forstarchiv, ISSN 0300-4112, Vol. 83, no 5, p. 163-169Article in journal (Refereed)
    Abstract [en]

    This article describes the current proportions of forest types with oak (Quercus robur and Q. petraea) in southern Sweden, provides an overview of oak distribution over time and reviews literature about oak regeneration relevant for the region. Further we discuss silvicultural possibilities to maintain and promote oak in Scandinavia. In Götaland pure oak forest covers 1% of the forest area and mixed forest types with > 10% oak proportion cover approximately 10% of the area. Common types of mixture are spruce-oak and pine-oak forest. Both mixtures are frequent in mature forest, especially pine-oak. Additionally, about one third of spruce-oak mixtures can be found in medium-aged forest. Intensive management would be necessary to promote single oak trees in old pine stands or spruce plantations, but the proportion of oak in coniferous forest provides some potential to maintain additional oak trees. The distribution of acorns by Jays, enhanced measures against browsing, and the release of single oak trees from competing tree species could help to maintain more oak trees for nature conservation. However, regarding management of oak for timber production, conventional methods are recommended. Planting after clear cutting of coniferous forest, or short shelter periods after mast years in oak stands, are established methods to regenerate pure oak stands. Another possibility to develop mature oak forest are mixed oak-spruce plantations, as traditionally practised in a small region in southern Sweden. The different approaches of oak management in Sweden were presented in April 2012 on the annual meeting of the section silviculture of DVFFA (German Union of Forest Research Organizations) in Wermsdorf near Leipzig to give an overview and access to recent forest research in Sweden.

  • 2.
    Furze, Morgan E.
    et al.
    Harvard university, USA.
    Jensen, Anna M.
    Oak Ridge National Laboratory, USA.
    Warren, JM
    Oak Ridge National Laboratory, USA.
    Richardson, Richardson
    Northern Arizona university, USA.
    Seasonal patterns of nonstructural carbohydrate reserves in four woody boreal species2018In: Journal of the Torrey Botanical Society, ISSN 1095-5674, E-ISSN 1940-0616, Vol. 145, no 4, p. 332-339Article in journal (Refereed)
    Abstract [en]

    Plants store nonstructural carbohydrates (NSCs), such as sugars and starch, to use as carbon and energy sources for daily maintenance and growth needs as well as during times of stress. Allocation of NSCs to storage provides an important physiological strategy associated with future growth and survival, and thus understanding the seasonal patterns of NSC reserves provides insight into how species with different traits (e.g., growth form, leaf habit, wood anatomy) may respond to stress. We characterized the seasonal patterns of NSCs in four woody boreal plant species in Minnesota, USA. Sugar and starch concentrations were measured across the year in the roots and branches of two conifer trees, black spruce (Picea mariana (Mill.) B.S.P.) and eastern tamarack (Larix laricina (Du Roi) K. Koch), as well as in the leaves and branches of two evergreen broadleaf shrubs, bog Labrador tea (Rhododendron groenlandicum (Oeder) Kron & Judd) and leatherleaf (Chamaedaphne calyculata (L.) Moench). In general, seasonal variation was dominated by changes in starch across all organs and species. While similar seasonal patterns of NSCs were observed in the shrubs, different seasonal patterns were observed between the trees, particularly in the roots. Our results suggest that species-specific traits likely have consequences for organ-level storage dynamics, which may influence whole-plant growth and survival under global change

  • 3.
    Griffiths, Natalie A.
    et al.
    Oak Ridge Natl Lab, USA.
    Hanson, Paul J.
    Oak Ridge Natl Lab, USA.
    Ricciuto, Daniel M.
    Oak Ridge Natl Lab, USA.
    Iversen, Colleen M.
    Oak Ridge Natl Lab, USA.
    Jensen, Anna M.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Oak Ridge Natl Lab, USA.
    Malhotra, Avni
    Oak Ridge Natl Lab, USA.
    McFarlane, Karis J.
    Lawrence Livermore Natl Lab, USA.
    Norby, Richard J.
    Oak Ridge Natl Lab, USA.
    Sargsyan, Khachik
    Sandia Natl Labs, USA.
    Sebestyen, Stephen D.
    USDA Forest Serv, USA.
    Shi, Xiaoying
    Oak Ridge Natl Lab, USA.
    Walker, Anthony P.
    Oak Ridge Natl Lab, USA.
    Ward, Eric J.
    Oak Ridge Natl Lab, USA.
    Warren, Jeffrey M.
    Oak Ridge Natl Lab, USA.
    Weston, David J.
    Oak Ridge Natl Lab, USA.
    Temporal and Spatial Variation in Peatland Carbon Cycling and Implications for Interpreting Responses of an Ecosystem-Scale Warming Experiment2017In: Soil Science Society of America Journal, ISSN 0361-5995, E-ISSN 1435-0661, Vol. 81, no 6, p. 1668-1688Article in journal (Refereed)
    Abstract [en]

    We are conducting a large-scale, long-term climate change response experiment in an ombrotrophic peat bog in Minnesota to evaluate the effects of warming and elevated CO2 on ecosystem processes using empirical and modeling approaches. To better frame future assessments of peatland responses to climate change, we characterized and compared spatial vs. temporal variation in measured C cycle processes and their environmental drivers. We also conducted a sensitivity analysis of a peatland C model to identify how variation in ecosystem parameters contributes to model prediction uncertainty. High spatial variability in C cycle processes resulted in the inability to determine if the bog was a C source or sink, as the 95% confidence interval ranged from a source of 50 g C m(-2) yr(-1) to a sink of 67 g C m(-2) yr(-1). Model sensitivity analysis also identified that spatial variation in tree and shrub photosynthesis, allocation characteristics, and maintenance respiration all contributed to large variations in the pretreatment estimates of net C balance. Variation in ecosystem processes can be more thoroughly characterized if more measurements are collected for parameters that are highly variable over space and time, and especially if those measurements encompass environmental gradients that may be driving the spatial and temporal variation (e.g., hummock vs. hollow microtopographies, and wet vs. dry years). Together, the coupled modeling and empirical approaches indicate that variability in C cycle processes and their drivers must be taken into account when interpreting the significance of experimental warming and elevated CO2 treatments.

  • 4.
    Götmark, Frank
    et al.
    University of Gothenburg, Sweden.
    Götmark, Elin
    Chalmers University of Technology, Sweden;University of Gothenburg, Sweden.
    Jensen, Anna M.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Why Be a Shrub?: a Basic Model and Hypotheses for the Adaptive Values of a Common Growth Form2016In: Frontiers in Plant Science, ISSN 1664-462X, E-ISSN 1664-462X, Vol. 7, article id 1095Article in journal (Refereed)
    Abstract [en]

    Shrubs are multi-stemmed short woody plants, more widespread than trees, important in many ecosystems, neglected in ecology compared to herbs and trees, but currently in focus due to their global expansion. We present a novel model based on scaling relationships and four hypotheses to explain the adaptive significance of shrubs, including a review of the literature with a test of one hypothesis. Our model describes advantages for a small shrub compared to a small tree with the same above-ground woody volume, based on larger cross-sectional stem area, larger area of photosynthetic tissue in bark and stem, larger vascular cambium area, larger epidermis (bark) area, and larger area for sprouting, and faster production of twigs and canopy. These components form our Hypothesis 1 that predicts higher growth rate for a small shrub than a small tree. This prediction was supported by available relevant empirical studies (14 publications). Further, a shrub will produce seeds faster than a tree (Hypothesis 2), multiple stems in shrubs insure future survival and growth if one or more stems die (Hypothesis 3), and three structural traits of short shrub stems improve survival compared to tall tree stems (Hypothesis 4)—all hypotheses have some empirical support. Multi-stemmed trees may be distinguished from shrubs by more upright stems, reducing bending moment. Improved understanding of shrubs can clarify their recent expansion on savannas, grasslands, and alpine heaths. More experiments and other empirical studies, followed by more elaborate models, are needed to understand why the shrub growth form is successful in many habitats.

  • 5.
    Götmark, Frank
    et al.
    University of Gothenburg.
    Schott, Kaitlin Muir
    University of Alberta, Canada.
    Jensen, Anna M.
    Swedish University of Agricultural Sciences.
    Factors influencing presence-absence of oak (Quercus spp.) seedlings after conservation-oriented partial cutting of high forests in Sweden2011In: Scandinavian Journal of Forest Research, ISSN 0282-7581, E-ISSN 1651-1891, Vol. 26, no 2, p. 136-145Article in journal (Refereed)
    Abstract [en]

    We studied occurrence of oak seedlings (Quercus robur L. and Q. petraea Liebl.) in 11 semi-natural oak-rich temperate forests in south Sweden after partial cutting (mean harvest; 26% of basal area). Earlier studies show that canopy openness is positively correlated with oak seedling performance. We used 20 pairs of subplots in each forest, with and without oak seedlings and matched with respect to canopy openness, to analyse other factors associated with seedling establishment and growth. The height of the ground layer (herbs and woody plants) had negative influence, i.e. higher height was associated with reduced probability of seedling occurrence. Higher soil water content had positive influence on seedling occurrence. Protection of seedlings by e.g. Rubus spp., twigs or dead wood was associated with lower seedling occurrence, but seedlings that did establish there tended to be taller. Type of ground vegetation and species composition did not differ between subplots with and without oak seedling. Thus, after conservation-oriented partial cutting of closed canopy high forests, increasing height of the ground vegetation disfavours oak seedlings (independent of canopy openness). High soil moisture favours oak seedlings, as does protected microsites for seedlings that can maintain high growth rate among their competitors.

  • 6.
    Hao, Meng-Shu
    et al.
    Lund University, Sweden.
    Jensen, Anna M.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Lund University, Sweden.
    Boquist, Ann-Sofie
    Lund University, Sweden.
    Liu, Yun-Jun
    Lund University, Sweden;Chinese Acad Agr Sci, Peoples Republi of China.
    Rasmusson, Allan G.
    Lund University, Sweden.
    The Ca2+-Regulation of the Mitochondrial External NADPH Dehydrogenase in Plants Is Controlled by Cytosolic pH2015In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, no 9, article id e0139224Article in journal (Refereed)
    Abstract [en]

    NADPH is a key reductant carrier that maintains internal redox and antioxidant status, and that links biosynthetic, catabolic and signalling pathways. Plants have a mitochondrial external NADPH oxidation pathway, which depends on Ca2+ and pH in vitro, but concentrations of Ca2+ needed are not known. We have determined the K-0.5(Ca2+) of the external NADPH dehydrogenase from Solanum tuberosum mitochondria and membranes of E. coli expressing Arabidopsis thaliana NDB1 over the physiological pH range using O-2 and decylubiquinone as electron acceptors. The K-0.5(Ca2+) of NADPH oxidation was generally higher than for NADH oxidation, and unlike the latter, it depended on pH. At pH 7.5, K-0.5(Ca2+) for NADPH oxidation was high (approximate to 100 mu M), yet 20-fold lower K-0.5(Ca2+) values were determined at pH 6.8. Lower K-0.5(Ca2+) values were observed with decylubiquinone than with O-2 as terminal electron acceptor. NADPH oxidation responded to changes in Ca2+ concentrations more rapidly than NADH oxidation did. Thus, cytosolic acidification is an important activator of external NADPH oxidation, by decreasing the Ca2+-requirements for NDB1. The results are discussed in relation to the present knowledge on how whole cell NADPH redox homeostasis is affected in plants modified for the NDB1 gene.

  • 7.
    Jensen, Anna M.
    SLU, Sweden.
    Effects of facilitation and competition on oak seedlings: Using shrubs as nurse-plants to facilitate growth and reduce browsing from large herbivores2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Plant–plant interactions have been indicated as a potential means to facilitate oak seedling establishment and reduce herbivory when restoring oak forests. The aim of this thesis was to investigate mechanisms and outcomes of competitive and indirectly facilitative interactions between oak (Quercus robur and Q. petraea) seedlings and neighboring plants, primarily shrubs. The associational resistance of planted oak seedlings to larger herbivores provided by naturally occurring shrubs was tested in ten temperate broadleaved forests across southern Sweden. The results showed that shrubs reduced ungulate browsing frequency and intensity by concealing the oak seedlings and by sharing enemies (i.e. ungulate herbivores) with surrounding and more preferred shrub species, thus providing numeric dilution and associational plant refuges. The occurrence of naturally regenerated oak seedlings, five years after a conservation-oriented thinning, was negatively influenced by the presence of tall ground vegetation and positively influenced by high soil moisture. For oak seedlings planted in an open field, shrubs indirectly facilitated biomass accumulation by reducing competition from herbaceous vegetation. However, shrubs became net competitors three years after planting. The oak seedling response, in terms of biomass accumulation, transpiration and photosynthesis, to competition from shrubs was proportional to resource availability. Aboveground competition for light had a greater effect on oak seedling growth than belowground competition. Nevertheless, oak seedlings were able to produce a second shoot flush, over-topping the shrub canopy. This periodic flushing enabled light-acclimation in a stratified light environment. In conclusion, management of shrubs has the potential to reduce browsing and herbaceous competitors during oak regeneration, particularly during the first years after planting. Although shrubs alone may not replace fences as an effective means of reducing browsing on oaks, they provide a complement to improve the growth of seedlings during the early stages of establishment.

  • 8.
    Jensen, Anna M.
    et al.
    Swedish University of Agricultural Sciences.
    Gardiner, Emile
    USDA Forest Service, Southern Research Station, Center for Bottomland Hardwoods Research, P.O. Box 227, Stoneville, MS 38776, USA.
    Vaughn, Kevin C.
    USDA Agricultural Research Service, Crop Production Systems Research Unit, P.O. Box 350, Stoneville, MS USA.
    High-light acclimation in Quercus robur L. seedlings upon over-topping a shaded environment.2012In: Environmental and Experimental Botany, ISSN 0098-8472, E-ISSN 1873-7307, Vol. 78, p. 25-32Article in journal (Refereed)
    Abstract [en]

    High developmental plasticity at the seedling-level during acclimation to the light environment may be an important determinant of seedling establishment and growth in temperate broadleaf forests, especially in dense understories where spatial light availability can vary greatly. Pedunculate oak (Quercus robur L.) seedlings were raised beneath a range of artificial light environments (high light, partial high light and low light) to examine morphological and photosynthetic acclimation to vertically stratified light availability. Acclimation observed at the seedling level included changes in proportional distribution of biomass and leaf area ratio to enhance either light gathering under low light availability or reduction of moisture stress under high light availability. Seedling-level acclimation was partially driven by plasticity at the flush level, but plasticity of traits determining flush morphology, such as leaf number, area, and mass, was largely controlled during bud formation rather than during shoot development. Therefore, flush-level acclimation was restricted when shoots elongated from a shaded environment into a high light environment. In contrast, traits influencing leaf-level acclimation, such as leaf thickness, specific leaf area, and pigment concentrations appeared to be driven primarily by the prevailing light environment during leaf development. The plastic response in leaf traits to light environments during shoot development enabled immediate acclimation of photosynthetic capacity to the prevailing light environment. In conclusion, oak seedlings displayed a large phenotypical plasticity on multiple levels that maximized whole seedling performance.

  • 9.
    Jensen, Anna M.
    et al.
    Swedish University of Agricultural Sciences.
    Götmark, Frank
    University of Gothenburg.
    Löf, Magnus
    Swedish University of Agricultural Sciences.
    Shrubs protect oak seedlings against ungulate browsing in temperate broadleaved forests of conservation interest: a field experiment2012In: Forest Ecology and Management, ISSN 0378-1127, E-ISSN 1872-7042, Vol. 266, p. 187-193Article in journal (Refereed)
    Abstract [en]

    In many oak-rich temperate broadleaved forests of conservation value, high ungulate browsing pressure restricts oak regeneration. We examined the protection of oak (Quercus sp.) seedlings from browsing provided by naturally occurring shrubs in 10 forests across southern Sweden over 3 years. We planted oak seedlings in four plots in each forest; two with naturally regenerated shrubs and two with no shrubs. Ungulate browsers were excluded from two plots at each site, one with and one without shrubs. Fencing provided the best protection against ungulate browsers for the seedlings. The probability of a seedling being browsed (browsing frequency) was approximately 20% units lower for individuals growing among shrubs than for individuals growing in the absence of shrubs. When browsing did occur, the intensity (measured as a reduction in height growth) was significantly lower for seedlings in shrubs. Regression analyses showed that browsing frequency increased on seedlings in tall shrubs, and decreased on seedlings that had been browsed previously. Browsing intensity decreased if the seedling grew in tall and dense shrubs. Browsing frequency and intensity increased on oak seedlings that over topped the shrub canopy. Increased abundance of the prickled Rubusidaeus and Rubusfruticosus coll. in plots with shrubs did not affect browsing frequency and intensity. Two and a half years after planting, oak seedling mortality increased by the presence of shrubs. Although shrubs restricted oak seedling growth, we conclude that shrubs initially facilitated oak regeneration by concealment, and subsequently by numeric dilution. Shrubs may be used to reduce browsing damages if long-term evaluation indicates a net positive outcome for oak survival and growth.

  • 10.
    Jensen, Anna M.
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Löf, Magnus
    Swedish University of Agricultural Sciences.
    Effects of interspecific competition from surrounding vegetation on mortality, growth and stem development in young oaks (Quercus robur)2017In: Forest Ecology and Management, ISSN 0378-1127, E-ISSN 1872-7042, Vol. 392, p. 176-183Article in journal (Refereed)
    Abstract [en]

    Facilitation by a neighboring woody understory has been suggested as a cost-effective and sustainable way to regenerate oaks. However, concerns about reduced plant growth and quality due to competing neighboring vegetation have hindered implementation. Here we studied competitive effects from herbaceous and woody vegetation on survival, growth, canopy development and stem quality in pedunculate oak (Quercus robur) in an open-field experiment in southern Sweden. Oaks were grown for eight years in four different competition treatments: no competing vegetation, with herbaceous vegetation (mainly grasses), with woody vegetation, and with both herbaceous and woody vegetation. During the first four years, competition had little effect on oak survival. However, after eight growing seasons, survival rates decreased to about 20% for oaks surrounded by woody vegetation, in contrast to oaks grown with only herbaceous vegetation that had a survival rate of near 100%. Competition from herbaceous and woody vegetation both reduced oak stem diameter and height growth, but they affected height growth differently. During the first growing seasons, oaks in the treatment with woody vegetation were able to keep up with the height growth of the surrounding vegetation. Thereafter, height growth stagnated, and after eight growing seasons heights of oaks in the treatment with woody competitors were only 30–39% that of oaks in the treatment without competing vegetation. In contrast, competition from herbaceous vegetation only restricted oak height development marginally. Interspecific competition not only restricted growth and survival but also shifted shoot architecture, resulting in a greater frequency of oaks with straight monopodial stems. Although competition from both herbaceous- and woody vegetation positively affected stem straightness, plots with woody vegetation had a greater proportion (0.42) of oaks with a single straight monopodial stem. Our results demonstrate that the facilitative competitive effects from herbaceous and woody vegetation could be used to control allocation patterns in young oaks, promoting development of tall straight monopodial stems. Considering the observed trade-off between high stem quality and survival, we recommend long-term assessment of this trade-off prior to application in practical forestry.

  • 11.
    Jensen, Anna M.
    et al.
    Swedish University of Agricultural Sciences.
    Löf, Magnus
    Swedish University of Agricultural Sciences.
    Gardiner, Emile
    Center for Bottomland Hardwoods Research, USA.
    Effects of above- and below-ground competition from shrubs on photosynthesis, transpiration and growth in Quercus robur L. seedlings2011In: Environmental and Experimental Botany, ISSN 0098-8472, E-ISSN 1873-7307, Vol. 71, no 3, p. 367-375Article in journal (Refereed)
    Abstract [en]

    For a tree seedling to successfully establish in dense shrubbery, it must maintain function under heterogeneous resource availability. We evaluated leaf-level acclimation in photosynthetic capacity, seedling-level transpiration, and seedling morphology and growth to gain an understanding of the effects of above- and below-ground competition on Quercus robur seedlings. Experimental seedlings were established in a typical southern Swedish shrub community where they received 1 of 4 competition levels (above-ground, below-ground, above- and below-ground, or no competition), and leaf-level responses were examined between two growth flushes. Two years after establishment, first-flush leaves from seedlings receiving above-ground competition showed a maximum rate of photosynthesis (Amax) 40% lower than those of control seedlings. With the development of a second flush above the shrub canopy,Amax of these seedlings increased to levels equivalent to those of seedlings free of light competition. Shrubby competition reduced oak seedling transpiration such that seedlings exposed to above- and below-ground competition showed rates 43% lower than seedlings that were not exposed to competition. The impaired physiological function of oak seedlings growing amid competition ultimately led to a 60–74% reduction in leaf area, 29–36% reduction in basal diameter, and a 38–78% reduction in total biomass accumulation, but root to shoot ratio was not affected. Our findings also indicate that above-ground competition reduced Amax, transpiration and biomass accumulation more so than below-ground competition. Nevertheless, oak seedlings exhibited the ability to develop subsequent growth flushes with leaves that had an Amax acclimated to utilize increased light availability. Our findings highlight the importance of flush-level acclimation under conditions of heterogeneous resource availability, and the capacity of oak seedlings to initiate a positive response to moderate competition in a shrub community.

  • 12.
    Jensen, Anna M.
    et al.
    Swedish University of Agricultural Sciences.
    Löf, Magnus
    Swedish University of Agricultural Sciences.
    Witzell, Johanna
    Swedish University of Agricultural Sciences.
    Effects of competition and indirect facilitation by shrubs on Quercus robur saplings2012In: Plant Ecology, ISSN 1385-0237, E-ISSN 1573-5052, Vol. 213, no 4, p. 535-543Article in journal (Refereed)
    Abstract [en]

    Indirect facilitation by shrubs has been suggested as a cost-effective way of regenerating oaks in forests of conservation interest. In this study, we tested whether shrubs can enhance growth in pedunculate oak (Quercus robur) by suppressing herbaceous competitors. We studied interactions between young oaks, shrubs, and/or herbaceous vegetation in an open-field experiment, in southern Sweden, over the first 3 years after planting. Oak saplings were grown in four competition treatments: no competing vegetation; with herbaceous vegetation; with shrubs; and with both herbaceous vegetation and shrubs. Competition from shrubs and herbaceous vegetation both reduced stem diameter and biomass accumulation, but they affected biomass partitioning differently. Saplings grown with competition from shrubs partitioned biomass primarily into height growth, while those saplings exposed to competition from herbaceous vegetation invested a relatively higher proportion in root growth. Competition between shrubs and herbaceous vegetation reduced the above-ground biomass of the herbaceous vegetation, resulting in an indirect facilitative effect for the oaks during the first 2 years after planting. However, during the third year, shrubs had a negative effect on biomass accumulation. In summary, results from this study suggest that shrubs indirectly facilitate biomass accumulation of oak saplings by suppressing herbaceous vegetation, possibly by reducing competition for below-ground resources. However, owing to the relatively short duration of positive net outcome for the oak, we recommend that a longer-term assessment of the interaction between oak regeneration and neighboring shrubs be made before the outcome of this study is applied to practical forestry.

  • 13.
    Jensen, Anna M.
    et al.
    Oak Ridge National Laboratory, USA.
    Warren, Jeffrey M.
    Oak Ridge National Laboratory, USA.
    Hanson, Paul
    Oak Ridge National Laboratory, USA.
    Childs, Joanne
    Oak Ridge National Laboratory, USA.
    Wullschleger, Stan
    Oak Ridge National Laboratory, USA.
    Needle age and season influence photosynthetic temperature response and total annual carbon uptake in mature Picea mariana trees2015In: Annals of Botany, ISSN 0305-7364, E-ISSN 1095-8290, Vol. 116, no 5, p. 821-832Article in journal (Refereed)
    Abstract [en]

    Background, Aims and Methods; The carbon (C) balance of boreal terrestrial ecosystems is sensitive to increasing temperature, but the direction and thresholds of responses are uncertain. Annual C uptake in Picea and other evergreen boreal conifers is dependent on seasonal- and cohort-specific photosynthetic and respiratory temperature response functions. To assess the physiological significance of maintaining multiple foliar cohorts we measured photosynthetic capacity, foliar respiration (Rd), and leaf biochemistry and morphology of mature Picea mariana trees within an ombrotrophic bog ecosystem in Minnesota, USA. Results were applied to a simple model of canopy photosynthesis to simulate annual C uptake by cohort age under ambient and elevated temperature scenarios.

    Key Results; Temperature responses of key photosynthetic parameters (i.e., light-saturated rate of CO2 assimilation (Asat), rate of Rubisco carboxylation (Vcmax), electron transport rate (Jmax)) were dependent on season and generally less responsive in the developing current-year (Y0) needles compared to one-year-old (Y1) or two-year-old (Y2) foliage. Temperature optimums ranged from 18.7 - 23.7, 31.3 - 38.3 and 28.7 - 36.7°C for Asat, Vcmax and Jmax, respectively. Foliar cohorts differed in their morphology and photosynthetic capacity, which resulted in 64% of modeled annual stand C uptake from Y1&2 cohorts (LAI 0.67 m2 m-2) and just 36% from the Y0 cohorts (LAI 0.52 m2 m-2). Under warmer climate change scenarios, the contribution of Y0 cohorts was even less; e.g., 31% of annual C uptake for a modeled 9°C rise in mean summer temperatures. Results suggest that net annual C uptake by P. mariana could increase under elevated temperature, and become more dependent on older foliar cohorts.

    Conclusions; Collectively, these results illustrate the physiological and ecological significance of different foliar cohorts, and indicate the need for seasonal- and cohort-specific model parameterization when estimating C uptake capacity of boreal forest ecosystems under ambient or future temperature scenarios.

  • 14.
    Jensen, Anna M.
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Oak Ridge National Laboratory, USA.
    Warren, Jeffrey M.
    Oak Ridge National Laboratory, USA.
    King, Anthony W.
    Oak Ridge National Laboratory, USA.
    Ricciuto,, Daniel M.
    Oak Ridge National Laboratory, USA.
    Hanson, Paul J.
    Oak Ridge National Laboratory, USA.
    Wullschleger, Stan D.
    Oak Ridge National Laboratory, USA.
    Simulated projections of boreal forest peatland ecosystem productivity are sensitive to observed seasonality in leaf physiology2019In: Tree Physiology, ISSN 0829-318X, E-ISSN 1758-4469, Vol. 39, no 4, p. 556-572Article in journal (Refereed)
    Abstract [en]

    We quantified seasonal CO2 assimilation capacities for seven dominant vascular species in a wet boreal forest peatland then applied data to a land surface model parametrized to the site (ELM-SPRUCE) to test if seasonality in photosynthetic parameters results in differences in simulated plant responses to elevated CO2 and temperature. We collected seasonal leaf-level gas exchange, nutrient content and stand allometric data from the field-layer community (i.e., Maianthemum trifolium (L.) Sloboda), understory shrubs (Rhododendron groenlandicum (Oeder) Kron and Judd, Chamaedaphne calyculata (L.) Moench., Kalmia polifolia Wangenh. and Vaccinium angustifolium Alton.) and overstory trees (Picea mariana (Mill.) B.S.P. and Larix laricina (Du Roi) K. Koch). We found significant interspecific seasonal differences in specific leaf area, nitrogen content (by area; Na) and photosynthetic parameters (i.e., maximum rates of Rubisco carboxylation (Vcmax25°C), electron transport (Jmax25°C) and dark respiration (Rd25°C)), but minimal correlation between foliar Na and Vcmax25°C, Jmax25°C or Rd25°C, which illustrates that nitrogen alone is not a good correlate for physiological processes such as Rubisco activity that can change seasonally in this system. ELM-SPRUCE was sensitive to the introduction of observed interspecific seasonality in Vcmax25°C, Jmax25°C and Rd25°C, leading to simulated enhancement of net primary production (NPP) using seasonally dynamic parameters as compared with use of static parameters. This pattern was particularly pronounced under simulations with higher temperature and elevated CO2, suggesting a key hypothesis to address with future empirical or observational studies as climate changes. Inclusion of species-specific seasonal photosynthetic parameters should improve estimates of boreal ecosystem-level NPP, especially if impacts of seasonal physiological ontogeny can be separated from seasonal thermal acclimation.

  • 15.
    Kumarathunge, Dushan P.
    et al.
    Western Sydney University, Australia;Coconut Research Institute of Sri Lanka, Sri Lanka.
    Medlyn, Belinda E.
    Western Sydney University, Australia.
    Drake, John E.
    State University of New York, USA.
    Tjoelker, Mark G.
    Western Sydney University, Australia.
    Aspinwall, Michael J.
    University of North Florida, USA.
    Battaglia, Michael
    CSIRO Agriculture and Food, Australia.
    Cano, Francisco J.
    Western Sydney University, Australia.
    Carter, Kelsey R.
    Michigan Technological University, USA.
    Cavaleri, Molly A.
    Michigan Technological University, USA.
    Cernusak, Lucas A.
    James Cook University, Australia.
    Chambers, Jeffrey Q.
    University of California Berkeley, USA.
    Crous, Kristine Y.
    Western Sydney University, Australia.
    De Kauwe, Martin G.
    University of New South Wales, Australia.
    Dillaway, Dylan N.
    Unity College, USA.
    Dreyer, Erwin
    Université de Lorraine, France.
    Ellsworth, David S.
    Western Sydney University, Australia.
    Ghannoum, Oula
    Western Sydney University, Australia.
    Han, Qingmin
    Forestry and Forest Products Research Institute (FFPRI), Japan.
    Hikosaka, Kouki
    Tohoku University, Japan.
    Jensen, Anna M.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Kelly, Jeff W. G.
    University of Washington, USA.
    Kruger, Eric L.
    University of Wisconsin‐Madison, USA.
    Mercado, Lina M.
    University of Exeter, UK;Centre for Ecology and Hydrology, UK.
    Onoda, Yusuke
    Kyoto University, Japan.
    Reich, Peter B.
    Western Sydney University, Australia.
    Rogers, Alistair
    Brookhaven National Laboratory, USA.
    Slot, Martijn
    Smithsonian Tropical Research Institute, Panama.
    Smith, Nicholas G.
    Texas Tech University, USA.
    Tarvainen, Lasse
    Swedish University of Agricultural Sciences, Sweden;University of Gothenburg, Sweden.
    Tissue, David T.
    Western Sydney University, USA.
    Togashi, Henrique F.
    Macquarie University, Australia.
    Tribuzy, Edgard S.
    Universidade Federal do Oeste do Pará (UFOPA), Brazil.
    Uddling, Johan
    University of Gothenburg, Sweden.
    Vårhammar, Angelica
    Western Sydney University, Australia.
    Wallin, Göran
    University of Gothenburg, Sweden.
    Warren, Jeffrey M.
    Oak Ridge National Laboratory, USA.
    Way, Danielle A.
    The University of Western Ontario, Canada;Duke University, USA.
    Acclimation and adaptation components of the temperature dependence of plant photosynthesis at the global scale2019In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 222, no 2, p. 768-784Article in journal (Refereed)
    Abstract [en]

    The temperature response of photosynthesis is one of the key factors determining predicted responses to warming in global vegetation models (GVMs). The response may vary geographically, owing to genetic adaptation to climate, and temporally, as a result of acclimation to changes in ambient temperature. Our goal was to develop a robust quantitative global model representing acclimation and adaptation of photosynthetic temperature responses.

    We quantified and modelled key mechanisms responsible for photosynthetic temperature acclimation and adaptation using a global dataset of photosynthetic CO2 response curves, including data from 141 C3 species from tropical rainforest to Arctic tundra. We separated temperature acclimation and adaptation processes by considering seasonal and common-garden datasets, respectively.

    The observed global variation in the temperature optimum of photosynthesis was primarily explained by biochemical limitations to photosynthesis, rather than stomatal conductance or respiration. We found acclimation to growth temperature to be a stronger driver of this variation than adaptation to temperature at climate of origin.

    We developed a summary model to represent photosynthetic temperature responses and showed that it predicted the observed global variation in optimal temperatures with high accuracy. This novel algorithm should enable improved prediction of the function of global ecosystems in a warming climate.

  • 16.
    Löf, Magnus
    et al.
    Swedish University of Agricultural Sciences, Southern Swedish Forest Research Center, Sweden.
    Bolte, Andreas
    Johann Heinrich von Thünen-Institut (TI), Federal Research Institute for Rural Areas, Forestry and Fisheries, Institute of Forest Ecosystems, Eberswalde, Germany.
    Jacobs, Douglass F.
    Hardwood Tree Improvement and Regeneration Center, Department of Forestry and Natural Resources, Purdue University, West Lafayette, IN, U.S.A.
    Jensen, Anna M.
    Oak Ridge National Laboratory, Climate Change Science Institute, Oak Ridge, TN, U.S.A.
    Nurse Trees as a Forest Restoration Tool for Mixed Plantations: Effects on Competing Vegetation and Performance in Target Tree Species2014In: Restoration Ecology, ISSN 1061-2971, E-ISSN 1526-100X, Vol. 22, no 6, p. 758-765Article in journal (Refereed)
    Abstract [en]

    Multi-species mixed plantations can be designed to meet social, economic, and environmental objectives during forest restoration. This paper reports results from an experiment in southern Sweden concerning the influence of three different fast growing nurse tree species on the cover of herbaceous vegetation and on the performance of several target tree species. After 10 years, the nurse trees had reduced the competing herbaceous vegetation but the effect was weak and it may take more than a decade to achieve effective vegetation control. The nurse tree species Betula pendula and Larix x eurolepis did improve stem form in some target tree species, but had a minor effect on survival and growth. The open conditions before crown closure of nurse trees strongly influence seedling performance and so delayed planting of target tree species may provide a means to avoid those conditions. Survival and growth differed greatly among the tree species. Besides the two nurse tree species mentioned above, high survival was found in Picea abies and Quercus robur and intermediate survival in Fagus sylvaticaTilia cordata, and in the N-fixing nurse tree Alnus glutinosa. Survival was low in the target tree species Fraxinus excelsior L. and Prunus avium. For restoration practitioners, our results illustrate the potential of using nurse trees for rapidly building a new forest structure and simultaneously increase productivity, which might be a cost-effective strategy for forest restoration.

  • 17.
    Löf, Magnus
    et al.
    Swedish University of Agricultural Sciences, Sweden.
    Brunet, Jörg
    Swedish University of Agricultural Sciences, Sweden.
    Hickler, Tomas
    Goethe-University Frankfurt, Germany.
    Birkedal, Maria
    Södra Skog, Sweden.
    Jensen, Anna M.
    Oak Ridge National Laboratory, USA.
    Restoring broadleaved forests in southern Sweden as climate changes2012In: A Goal-Oriented Approach to Forest Landscape Restoration / [ed] Stanturf, J., Madsen, P. and Lamb, D. (Eds.), Springer, 2012, p. 373-391Chapter in book (Refereed)
    Abstract [en]

    Temperate broadleaved forests in southern Sweden are important for biodiversity and policies have, so far, been concentrated on protecting the few valuable forests that still remain. This approach is now being challenged by rapid climate change. Using a vegetation model, we present transient and potential long-term predictions for changes in the natural distribution of different tree species and forest composition. Our model analyses show that temperate broadleaved tree species will be able to be established further north than their present distribution. In addition, this region will probably be an area of high species turnover, with the loss of boreal species and gains of temperate species. New broadleaved forests need to be restored in order to enhance reintegration. Current forest policies may not be relevant under a climate change scenario. Research is needed in climate change impacts on species and habitats, habitat restoration, migration of species, alternative silvicultural systems and efficient regeneration systems. It would probably be too expensive for the society to rely only on governmental resources for sustainable landscape level restorations programs. Instead a pragmatic approach, which considers the economic aspects of private forest owners, as well as other goals, should be adopted. In addition, policies must be based on a holistic understanding of the interactions between management, climate change and biodiversity.

  • 18.
    Norby, Richard J.
    et al.
    Oak Ridge National Laboratory, USA.
    Gu, Lianhong
    Oak Ridge National Laboratory, USA.
    Haworth, Ivan C.
    Oak Ridge National Laboratory, USA.
    Jensen, Anna M.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Oak Ridge National Laboratory, USA.
    Turner, Benjamin L.
    Smithsonian Tropical Research Institute, Panama.
    Walker, Anthony P.
    Oak Ridge National Laboratory, USA.
    Warren, Jeffrey M.
    Oak Ridge National Laboratory, USA.
    Weston, David J.
    Oak Ridge National Laboratory, USA.
    Xu, Chonggang
    Los Alamos National Laboratory, USA.
    Winter, Klaus
    Smithsonian Tropical Research Institute, Panama.
    Informing models through empirical relationships between foliar phosphorus, nitrogen and photosynthesis across diverse woody species in tropical forests of Panama2017In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 215, no 4, p. 1425-1437Article in journal (Refereed)
    Abstract [en]

    Our objective was to analyze and summarize data describing photosynthetic parameters and foliar nutrient concentrations from tropical forests in Panama to inform model representation of phosphorus (P) limitation of tropical forest productivity.

    Gas exchange and nutrient content data were collected from 144 observations of upper canopy leaves from at least 65 species at two forest sites in Panama, differing in species composition, rainfall and soil fertility. Photosynthetic parameters were derived from analysis of assimilation rate vs internal CO2 concentration curves (A/Ci), and relationships with foliar nitrogen (N) and P content were developed.

    The relationships between area-based photosynthetic parameters and nutrients were of similar strength for N and P and robust across diverse species and site conditions. The strongest relationship expressed maximum electron transport rate (Jmax) as a multivariate function of both N and P, and this relationship was improved with the inclusion of independent data on wood density.

    Models that estimate photosynthesis from foliar N would be improved only modestly by including additional data on foliar P, but doing so may increase the capability of models to predict future conditions in P-limited tropical forests, especially when combined with data on edaphic conditions and other environmental drivers.

  • 19.
    Sun, Ying
    et al.
    University of Texas at Austin, Austin, USA.
    Gu, Lianhong
    Oak Ridge National Laboratory, USA.
    Dickinson, Robert E.
    University of Texas at Austin, USA.
    Pallardy, Stephen G.
    University of Missouri, USA.
    Baker, John
    University of Minnesota, USA.
    Cao, Yonghui
    Chinese Academy of Forestry, China.
    Damatta, Fábio Murilo
    Universidade Federal de Viçosa, Brazil.
    Dong, Xuejun
    North Dakota State University, USA.
    Ellsworth, David
    University of Western Sydney, Australia.
    Van Goethem, Davina
    University of Antwerp, Belgium.
    Jensen, Anna M.
    Oak Ridge National Laboratory, USA.
    Law, Beverly E.
    Oregon State University, USA.
    Loos, Rodolfo
    Technology Center, Fibria Celulose S.A, Aracruz, Brazil.
    Martins, Samuel C. Vitor
    Universidade Federal de Viçosa, Brazil.
    Norby, Richard J.
    Oak Ridge National Laboratory, USA.
    Warren, Jeffrey M.
    Oak Ridge National Laboratory, USA.
    Weston, David
    Oak Ridge National Laboratory, USA.
    Winter, Klaus
    Smithsonian Tropical Research Institute, Republic of Panama.
    Asymmetrical effects of mesophyll conductance on fundamental photosynthetic parameters and their relationships estimated from leaf gas exchange measurements2014In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 37, no 4, p. 978-994Article in journal (Refereed)
    Abstract [en]

    Worldwide measurements of nearly 130 C3 species covering all major plant functional types are analysed in conjunction with model simulations to determine the effects of mesophyll conductance (gm) on photosynthetic parameters and their relationships estimated fromA/Ci curves. We find that an assumption of infinite gm results in up to 75% underestimation for maximum carboxylation rate Vcmax, 60% for maximum electron transport rate Jmax, and 40% for triose phosphate utilization rate TuVcmax is most sensitive, Jmax is less sensitive, and Tuhas the least sensitivity to the variation of gm. Because of this asymmetrical effect of gm, the ratios of Jmax to VcmaxTu to Vcmax and Tu toJmax are all overestimated. An infinite gm assumption also limits the freedom of variation of estimated parameters and artificially constrains parameter relationships to stronger shapes. These findings suggest the importance of quantifying gm for understanding in situphotosynthetic machinery functioning. We show that a nonzero resistance to CO2 movement in chloroplasts has small effects on estimated parameters. A non-linear function with gm as input is developed to convert the parameters estimated under an assumption of infinite gm to proper values. This function will facilitate gm representation in global carbon cycle models.

  • 20.
    Warren, Jeffrey M.
    et al.
    Oak Ridge National Laboratory, USA.
    Jensen, Anna M.
    Oak Ridge National Laboratory, USA.
    Medlyn, Belinda E.
    Macquarie University, Australia.
    Norby, Richard J.
    Oak Ridge National Laboratory, USA.
    Tissue, David T.
    University of Western Sydney, Australia.
    Carbon dioxide stimulation of photosynthesis in Liquidambar styraciflua is not sustained during a 12-year field experiment2015In: AoB Plants, ISSN 2041-2851, E-ISSN 2041-2851, Vol. 7, article id plu074Article in journal (Refereed)
    Abstract [en]

    Elevated atmospheric CO2 (eCO2) often increases photosynthetic CO2assimilation (A) in field studies of temperate tree species. However, there is evidence that A may decline through time due to biochemical and morphological acclimation, and environmental constraints. Indeed, at the free-air CO2 enrichment (FACE) study in Oak Ridge, Tennessee, A was increased in 12-year-old sweetgum trees following 2 years of ∼40 % enhancement of CO2A was re-assessed a decade later to determine if the initial enhancement of photosynthesis by eCO2 was sustained through time. Measurements were conducted at prevailing CO2 and temperature on detached, re-hydrated branches using a portable gas exchange system. Photosynthetic CO2 response curves (A versus the CO2 concentration in the intercellular air space (Ci); or ACi curves) were contrasted with earlier measurements using leaf photosynthesis model equations. Relationships between light-saturated photosynthesis (Asat), maximum electron transport rate (Jmax), maximum Rubisco activity (Vcmax), chlorophyll content and foliar nitrogen (N) were assessed. In 1999, Asat for eCO2treatments was 15.4 ± 0.8 μmol m−2 s−1, 22 % higher than aCO2treatments (P < 0.01). By 2009, Asat declined to <50 % of 1999 values, and there was no longer a significant effect of eCO2 (Asat = 6.9 or 5.7 ± 0.7 μmol m−2 s−1 for eCO2 or aCO2, respectively). In 1999, there was no treatment effect on area-based foliar N; however, by 2008, N content in eCO2 foliage was 17 % less than that in aCO2 foliage. Photosynthetic N-use efficiency (Asat : N) was greater in eCO2 in 1999 resulting in greaterAsat despite similar N content, but the enhanced efficiency in eCO2 trees was lost as foliar N declined to sub-optimal levels. There was no treatment difference in the declining linear relationships between Jmax or Vcmax with declining N, or in the ratio of Jmax : Vcmax through time. Results suggest that the initial enhancement of photosynthesis to elevated CO2 will not be sustained through time if N becomes limited.

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