Teis N. Mikkelsen

Georg-August-Universität Göttingen, Göttingen, Lower Saxony, Germany

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Publications (82)182.91 Total impact

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    ABSTRACT: The terrestrial vegetation is a source of UV radiation-induced aerobic methane (CH4 ) release to the atmosphere. Hitherto pectin, a plant structural component, has been considered as the most likely precursor for this CH4 release. However, most of the leaf pectin is situated below the surface wax layer, and UV transmittance of the cuticle differs among plant species. In some species, the cuticle effectively absorbs and/or reflects UV radiation. Thus, pectin may not necessarily contribute substantially to the UV radiation-induced CH4 emission measured at surface level in all species. Here, we investigated the potential of the leaf surface wax itself as a source of UV radiation-induced leaf aerobic CH4 formation. Isolated leaf surface wax emitted CH4 at substantial rates in response to UV radiation. This discovery has implications for how the phenomenon should be scaled to global levels. In relation to this, we demonstrated that the UV radiation-induced CH4 emission is independent of leaf area index above unity. Further, we observed that the presence of O2 in the atmosphere was necessary for achieving the highest rates of CH4 emission. Methane formation from leaf surface wax is supposedly a two-step process initiated by a photolytic rearrangement reaction of the major component followed by an α-cleavage of the generated ketone.
    Plant Biology 01/2014; · 2.32 Impact Factor
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    ABSTRACT: The projected future climate will affect the global agricultural production negatively, however, to keep abreast of the expected increase in global population, the agricultural production must increase. Therefore, to safeguard the future crop yield and quality, the adaptive potential of crops to environmental change needs to be explored in order to select the most productive genotypes. Presently, it is unknown whether cereal crops like spring barley can adapt to climate stressors over relatively few generations. To evaluate if strong selection pressures could change the performance of barley to environmental stress, we conducted a selection experiment over five plant generations (G0–G4) in three scenarios, where atmospheric [CO2] and temperature were increased as single factors and in combination. The treatments represented the expected environmental characteristics in Northern Europe around year 2075 [700 ppm CO2, 22/17 °C (day/night)] as well as a control mimicking present day conditions (390 ppm CO2, 19/12 °C). Two different barley accessions, a modern cultivar and an old landrace, were evaluated in terms of yield and biomass production. In all treatments representing future environmental scenarios, the G4-generation of selected plants did not improve its reproductive output compared to the G0-generation, as G4 produced less seeds and had a lower yield than unselected plants. These results indicate that barley might not respond positively to rapid and strong selection by elevated [CO2] and temperature, contrary to previous results from oilseed rape. The two barley accessions analyzed presented almost the same response pattern in a given treatment, though the modern cultivar had the highest yield in the climate scenarios, while the landrace was superior in yield under present day climate conditions.
    Genetic Resources and Crop Evolution 01/2014; 61(1). · 1.59 Impact Factor
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    ABSTRACT: Plant responses to warming, elevated CO2, and changes in summer precipitation patterns involve complex interactions. In this study we aim to reveal the single factor responses and their interactive effects on photosystem II (PSII) performance during an autumn-to-winter period. The study was carried out in the CLIMAITE multifactor experiment, which includes the combined impact of elevated CO2 (free air carbon enrichment; CO2), warming (passive nighttime warming; T) and summer drought (rain-excluding curtains; D) in a temperate heath ecosystem. PSII performance was probed by the effective quantum yield in light, Fv′/Fm′, using the pulse amplitude methodology, and the total performance index, PItotal, which integrate changes of the chlorophyll-a fluorescence transient including the maximal quantum yield in darkness, Fv/Fm. Decreasing temperature during autumn linearly reduced PItotal, both in the wavy hair-grass, Deschampsia flexuosa, and in the evergreen dwarf shrub common heather, Calluna vulgaris, and following freezing events the PItotal and Fv′/Fm′ were reduced even more. Contrary to expected, indirect effects of the previous summer drought reduced PSII performance before freezing events, particularly in Calluna. In combinations with elevated CO2 interactive effects with drought, D × CO2 and warming, T × D × CO2, were negatively skewed and caused the reduction of PSII performance in both species after occurrence of freezing events. Neither passive nighttime warming nor elevated CO2 as single factors reduced PSII performance via incomplete cold hardening as hypothesized. Instead, the passive nighttime warming strongly increased PSII performance, especially after freezing events, and when combined with elevated CO2 a strongly skewed positive T × CO2 interactive effect was seen. This indicates that these plants take advantage of the longer growing season induced by the warming in elevated CO2 until a winter frost period becomes permanent. However, if previously exposed to summer drought this positive effect reverses via interactive D × CO2 and T × D × CO2 effects immediately after freezing events, causing the full combination of TDCO2 not to differ from the control. In a future warmer climate with high CO2 and summer drought, the occurrence of freezing events thus seem highly decisive for reducing PSII performance in the autumn-to-winter period. Such a reduced robustness of PSII performance may be highly decisive for the magnitude of the late season photosynthetic carbon uptake and reduce the growing season length in these temperate heath plants.
    Environmental and Experimental Botany 09/2013; 93:1-12. · 2.58 Impact Factor
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    ABSTRACT: Infrared reflective (IR) curtains have been widely used to obtain passive nighttime warming in field ecosystem experiments in order to simulate and study climate warming effects on ecosystems. For any field installation with IR-reflective curtains in an ecosystem the achieved heating effect depends on the heat gain determined by the stored energy during daytime (incoming radiation can be used as a proxy) the heat conservation determined by the IR-reflective effect of the curtains (cloudiness can be used as a proxy) and the heat loss determined by convectional heat loss (wind speed can be used as a proxy). In this study, we demonstrate some feasible avenues for improving the achieved temperature increase (�T) when using IR-reflective curtains at field scale by attacking the three main factors determining the efficiency of the curtains: (i) improving the long wave IR reflection by the curtains, (ii) insulating the curtains and (iii) reducing the lateral wind speed. We provide experimentally based replies to the major concerns raised in the literature about the passive nighttime warming method. We show (a) that using IR-reflective curtains during night does in fact not result in nighttime warming only as there is a small carryover (<0.5 ◦C) into the following daytime, and (b) although the employment of IR-reflective curtains at nighttime may alter the RH, it is a small change and not always in the same direction.
    Agricultural and Forest Meteorology 05/2013; 173:53-62. · 3.42 Impact Factor
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    ABSTRACT: Functional plant traits are likely to adapt under the sustained pressure imposed by environmental changes through natural selection. Employing Brassica napus as a model, a multi-generational study was performed to investigate the potential trajectories of selection at elevated [CO2] in two different temperature regimes. To reveal phenotypic divergence at the manipulated [CO2] and temperature conditions, a full-factorial natural selection regime was established in a phytotron environment over the range of four generations. It is demonstrated that a directional response to selection at elevated [CO2] led to higher quantities of reproductive output over the range of investigated generations independent of the applied temperature regime. The increase in seed yield caused an increase in aboveground biomass. This suggests quantitative changes in the functions of carbon sequestration of plants subjected to increased levels of CO2 over the generational range investigated. The results of this study suggest that phenotypic divergence of plants selected under elevated atmospheric CO2 concentration may drive the future functions of plant productivity to be different from projections that do not incorporate selection responses of plants. This study accentuates the importance of phenotypic responses across multiple generations in relation to our understanding of biogeochemical dynamics of future ecosystems. Furthermore, the positive selection response of reproductive output under increased [CO2] may ameliorate depressions in plant reproductive fitness caused by higher temperatures in situations where both factors co-occur.
    Ecology and Evolution 05/2013; 3(5):1163-72. · 1.66 Impact Factor
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    ABSTRACT: The impact of climate change on herbivorous insects can have far-reaching consequences for ecosystem processes. However, experiments investigating the combined effects of multiple climate change drivers on herbivorous insects are scarce. We independently manipulated three climate change drivers (CO2, warming, drought) in a Danish heathland ecosystem. The experiment was established in 2005 as a full factorial split-plot with 6 blocks 9 2 levels of CO2 9 2 levels of warming 9 2 levels of drought = 48 plots. In 2008, we exposed 432 larvae (n = 9 per plot) of the heather beetle (Lochmaea suturalis THOMSON), an important herbivore on heather, to ambient versus elevated drought, temperature, and CO2 (plus all combinations) for 5 weeks. Larval weight and survival were highest under ambient conditions and decreased significantly with the number of climate change drivers. Weight was lowest under the drought treatment, and there was a three-way interaction between time, CO2, and drought. Survival was lowest when drought, warming, and elevated CO2 were combined. Effects of climate change drivers depended on other co-acting factors and were mediated by changes in plant secondary compounds, nitrogen, and water content. Overall, drought was the most important factor for this insect herbivore. Our study shows that weight and survival of insect herbivores may decline under future climate. The complexity of insect herbivore responses increases with the number of combined climate change drivers.
    Ecology and Evolution 04/2013; 3(6):1149-1160. · 1.66 Impact Factor
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    ABSTRACT: High air concentrations of ammonium were detected at low and high altitude sites in Sweden, Finland and Norway during the spring 2006, coinciding with polluted air from biomass burning in eastern Europe passing over central and northern Fennoscandia. Unusually high values for throughfall deposition of ammonium were detected at one low altitude site and several high altitude sites in north Sweden. The occurrence of the high ammonium in throughfall differed between the summer months 2006, most likely related to the timing of precipitation events. The ammonia dry deposition may have contributed to unusual visible injuries on the tree vegetation in northern Fennoscandia that occurred during 2006, in combination with high ozone concentrations. It is concluded that long-range transport of ammonium from large-scale biomass burning may contribute substantially to the nitrogen load at northern latitudes.
    Environmental Pollution 02/2013; 176C:71-79. · 3.73 Impact Factor
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    ABSTRACT: There is an ongoing debate on how to correct leaf gas-exchange measurements for the unavoidable diffusion leakage that occurs when measurements are done in non-ambient CO(2) -concentrations. In this study we present a theory on how the CO(2) diffusion gradient over the gasket is affected by leaf mediated pores (LMP) and how LMP reduce diffusive exchange across the gaskets. Recent discussions have so far neglected the processes in the quasi-laminar boundary layer around the gasket. Counter intuitively, LMP reduce the leakage through gaskets, which can be explained by assuming that the boundary layer at the exterior of the cuvette is enriched with air from the inside of the cuvette. The effect can thus be reduced by reducing the boundary layer thickness. The theory clarifies conflicting results from earlier studies. We developed leaf adaptor frames that eliminate LMP during measurements on delicate plant material such as grass leaves with circular cross section, and the effectiveness is shown with respiration measurements on a harp of Deschampsia flexuosa leaves. We conclude that the best solution for measurements with portable photosynthesis systems is to avoid LMP rather than trying to correct for the effects.
    Plant Cell and Environment 01/2013; · 5.14 Impact Factor
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    Agricultural and Forest Meteorology 01/2013; 173:53– 62. · 3.42 Impact Factor
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    D. Bruhn, K. R. Albert, T. N. Mikkelsen, P. Ambus
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    ABSTRACT: The global burden of carbon monoxide, CO, is rather uncertain. In this paper we address the potential of UV-induced CO emission by terrestrial surfaces. Real-time measurements of [CO] were made with a cavity enhanced laser connected in closed loop to either an ecosystem chamber or a leaf scale chamber. Sand and leaves of all examined plant species exhibited emission of CO in response to artificial UV-radiation and the UV-component of natural solar radiation. The UV-induced rate of CO emission exhibited a rather low dependence on temperature, indicating an abiotic process. The emission of CO in response to the UV-component of natural solar radiation was also evident at the ecosystem scale. When scaled to the global level, the UV-induced emission of CO by the major types of terrestrial surfaces, living leaves and soil (here represented by sand), amounts up to 28 Tg yr-1. This source has till now not been accounted for by IPCC, but is equivalent to 14-56% of the 50-200 Tg yr-1 from sources currently accounted for (IPCC 2001). In addition to this are other known sources that ought to be considered. The hitherto unaccounted for terrestrial sources of CO amounts up to 207 Tg yr-1, almost two-thirds of the latest estimated global CO burden of 360 Tg yr-1 (IPCC, 2001).
    Biogeosciences Discussions 07/2012; 9(7):8449-8473.
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    ABSTRACT: Climate change has been shown to affect ecosystem process rates 1 and community composition 2 , with direct and indirect effects on belowground food webs 3 . In particular, altered rates of herbivory under future climate 4 can be expected to influence above–belowground interactions 5 . Here, we use a multifactor, field-scale climate change experiment and inde-pendently manipulate atmospheric CO 2 concentration, air and soil temperature and drought in all combinations since 2005. We show that changes in these factors modify the interaction between above-and belowground organisms. We use an insect herbivore to experimentally increase aboveground herbivory in grass phytometers exposed to all eight combinations of climate change factors for three years. Aboveground herbivory increased the abundance of belowground protozoans, micro-bial growth and microbial nitrogen availability. Increased CO 2 modified these links through a reduction in herbivory and cas-cading effects through the soil food web. Interactions between CO 2 , drought and warming can affect belowground protozoan abundance. Our findings imply that climate change affects aboveground–belowground interactions through changes in nutrient availability. Plant species composition and community structure in terres-trial environments have been predicted to shift in response to climate change 6 . Recent climate change experiments have shown the effects of drought, warming and increased CO 2 on plant productivity 7 , nitrogen cycling 8 and species interactions 4 . However, multifactor experiments on climate change are scarce 9 and climate change effects on interactions between the above-and the below-ground subsystem 5,10,11 are rarely considered. Most terrestrial plant species control or mediate the interaction between above-and belowground subsystems, for example through altered litter quality 5 or root exudates 12 , suggesting that changes in the aboveground compartment will cascade between the aboveground-and the belowground compartment 13 . For example, herbivores feeding on aboveground plant parts have been shown to induce changes in a wide range of processes in the root zone, affecting rhizodeposition 12 and soil decomposer organisms 14 . Furthermore, indirect pathways from herbivores through greenfall, frass or litter input to the belowground subsystem have been reported 5 . Increased CO 2 (ref. 15), increased temperature 16 or drought 17 have been shown to affect aboveground herbivory. Owing to the strong link between aboveground herbivory and belowground processes, it is likely that such climatic or atmospheric changes will lead to herbivory-induced changes in belowground processes
    Nature Climate Change. 05/2012;
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    ABSTRACT: The long-term and diurnal responses of photosystem II (PSII) performance to near-ambient UV-B radiation were investigated in High Arctic Betula nana. We conducted an UV exclusion experiment with five replicated blocks consisting of open control (no filter), photosynthetic active radiation and UV-B transparent filter control (Teflon), UV-B-absorbing filter (Mylar) and UV-AB-absorbing filter (Lexan). Ethylenediurea (EDU), a chemical normally used to protect plants against ozone injury, was sprayed on the leaves both in the field and in an additional laboratory study to investigate if EDU mitigated the effects of UV-B. Chlorophyll-a fluorescence induction curves were used for analysis of OJIP test parameters. Near-ambient UV-B radiation reduced across season maximum quantum yield (TR(o) /ABS = F(v) /F(m)), approximated number of active PSII reaction center (RC/ABS) and the performance index (PI(ABS)), despite improved leaf screening against UV-B with higher content of UV-B-absorbing compounds and a lower specific leaf area. EDU application counteracted the negative impact of UV-B on TR(o) /ABS, RC/ABS and PI(ABS) . This indicates that the mechanisms behind UV-B and ozone damage share some common features. The midday depression was present in all treatments, but TR(o) /ABS and PI(ABS) were persistently lower in near-ambient UV-B compared to UV-B reduction. The recovery phase was particularly impaired in near-ambient UV-B and interactive effects between treatment × hour raised TR(o) /ABS, RC/ABS and PI(ABS) higher in reduced UV-B compared to near-ambient UV-B. This demonstrates current solar UV-B to reduce the PSII performance both on a daily as well as a seasonal basis in this High Arctic species.
    Physiologia Plantarum 02/2012; 145(3):485-500. · 3.66 Impact Factor
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    ABSTRACT: The evidence that is currently available demonstrates that future changes in precipitation patterns will affect plant carbon uptake. However, the outcome in terms of success, productivity and fecundity depends upon individual species and different responses of various growth forms. Examination of these differences in response in dry versus rewetting conditions can be used to highlight the limitations coherent in different strategies adopted by, for example, evergreen shrubs and grasses. We investigated the leaf-level photosynthetic performance, leaf C, N and δ13C along with vegetation cover and biomass in the evergreen dwarf shrub Calluna vulgaris and the grass species Deschampsia flexuosa in a temperate heath during seasonal changes in soil moisture. Higher photosynthetic capacity compensated for lower stomatal conductance and sustained higher rates of photosynthesis in the grass compared to the dwarf shrub. In combination with dieback of aboveground biomass and reduction of stomatal conductance reduction during dry conditions, the grass continued to have high carbon uptake in the remaining leaves. The dwarf shrub endured the dry conditions by preserving shoot biomass and reducing stomatal conductance. Soil rewetting increased leaf nitrogen and photosynthesis in the grass much more than for the dwarf shrub. These different strategies may have a considerable impact on carbon uptake and on the ability of a species to compete, as future climatic changes are likely to extend the summer drought period together with the more frequent and extensive precipitation events outside the summer season. --------------------------------------------------------------------------------
    Acta Oecologica 01/2012; 45:79-85. · 1.62 Impact Factor
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    ABSTRACT: This study investigated the impact of predicted future climatic and atmospheric conditions on soil respiration (RS) in a Danish Calluna-Deschampsia-heathland. A fully factorial in situ experiment with treatments of elevated atmospheric CO2 (+130 ppm), raised soil temperature (+0.4 °C) and extended summer drought (5–8% precipitation exclusion) was established in 2005. The average RS, observed in the control over 3 years of measurements (1.7 μmol CO2 m−2 sec−1), increased 38% under elevated CO2, irrespective of combination with the drought or temperature treatments. In contrast, extended summer drought decreased RS by 14%, while elevated soil temperature did not affect RS overall. A significant interaction between elevated temperature and drought resulted in further reduction of RS when these treatments were combined. A detailed analysis of short-term RS dynamics associated with drought periods showed that RS was reduced by ~50% and was strongly correlated with soil moisture during these events. Recovery of RS to pre-drought levels occurred within 2 weeks of rewetting; however, unexpected drought effects were observed several months after summer drought treatment in 2 of the 3 years, possibly due to reduced plant growth or changes in soil water holding capacity. An empirical model that predicts RS from soil temperature, soil moisture and plant biomass was developed and accounted for 55% of the observed variability in RS. The model predicted annual sums of RS in 2006 and 2007, in the control, were 672 and 719 g C m−2 y−1, respectively. For the full treatment combination, i.e. the future climate scenario, the model predicted that soil respiratory C losses would increase by ~21% (140–150 g C m−2 y−1). Therefore, in the future climate, stimulation of C storage in plant biomass and litter must be in excess of 21% for this ecosystem to not suffer a reduction in net ecosystem exchange.
    Global Change Biology 01/2012; 18:1216-1230. · 6.91 Impact Factor
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    ABSTRACT: Climate change scenarios predict simultaneously increase in temperature, altered precipitation patterns and elevated atmospheric CO2 concentration, which will affect key ecosystem processes and plant growth and species interactions. In a large-scale experiment, we investigated the effects of in situ exposure to elevated atmospheric CO2 concentration, increased temperature and prolonged drought periods on the plant biomass in a dry heathland (Brandbjerg, Denmark). Results after 3 years showed that drought reduced the growth of the two dominant species Deschampsia flexuosa and Calluna vulgaris. However, both species recovered quickly after rewetting and the drought had no significant effect on annual aboveground biomass production. We did not observe any effects of increased temperature. Elevated CO2 stimulated the biomass production for D. flexuosa in one out of three years but did not influence the standing biomass for either D. flexuosa or the ecosystem as more litter was produced. Treatment combinations showed little interactions on the measured parameters and in particular elevated CO2 did not counterbalance the drought effect on plant growth, as we had anticipated. The plant community did not show any significant responses to the imposed climate changes and we conclude that the two heathland species, on a short time scale, will be relatively resistant to the changes in climatic conditions.
    Ecosystems 01/2012; 15(2). · 3.17 Impact Factor
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    ABSTRACT: Forests in Europe face significant changes in climate, which in interaction with air quality changes, may significantly affect forest productivity, stand composition and carbon sequestration in both vegetation and soils. Identified knowledge gaps and research needs include: (i) interaction between changes in air quality (trace gas concentrations), climate and other site factors on forest ecosystem response, (ii) significance of biotic processes in system response, (iii) tools for mechanistic and diagnostic understanding and upscaling, and (iv) the need for unifying modelling and empirical research for synthesis. This position paper highlights the above focuses, including the global dimension of air pollution as part of climate change and the need for knowledge transfer to enable reliable risk assessment. A new type of research site in forest ecosystems ("supersites") will be conducive to addressing these gaps by enabling integration of experimentation and modelling within the soil-plant-atmosphere interface, as well as further model development.
    Environmental Pollution 01/2012; 160(1):57-65. · 3.73 Impact Factor
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    ABSTRACT: The evidence that is currently available demonstrates that future changes in precipitation patterns will affect plant carbon uptake. However, the outcome in terms of success, productivity and fecundity depends upon individual species and different responses of various growth forms. Examination of these differences in response in dry versus rewetting conditions can be used to highlight the limitations coherent in different strategies adopted by, for example, evergreen shrubs and grasses. We investigated the leaf-level photosynthetic performance, leaf C, N and δ13C along with vegetation cover and biomass in the evergreen dwarf shrub Calluna vulgaris and the grass species Deschampsia flexuosa in a temperate heath during seasonal changes in soil moisture.Higher photosynthetic capacity compensated for lower stomatal conductance and sustained higher rates of photosynthesis in the grass compared to the dwarf shrub. In combination with dieback of aboveground biomass and reduction of stomatal conductance reduction during dry conditions, the grass continued to have high carbon uptake in the remaining leaves. The dwarf shrub endured the dry conditions by preserving shoot biomass and reducing stomatal conductance. Soil rewetting increased leaf nitrogen and photosynthesis in the grass much more than for the dwarf shrub.These different strategies may have a considerable impact on carbon uptake and on the ability of a species to compete, as future climatic changes are likely to extend the summer drought period together with the more frequent and extensive precipitation events outside the summer season.
    Acta Oecologica 01/2012; 45:79-87. · 1.62 Impact Factor

Publication Stats

748 Citations
182.91 Total Impact Points

Institutions

  • 2013
    • Georg-August-Universität Göttingen
      • Department of Crop Sciences
      Göttingen, Lower Saxony, Germany
  • 2007–2009
    • Technical University of Denmark
      • National Laboratory for Sustainable Energy
      Copenhagen, Capital Region, Denmark
  • 1995–2008
    • University of Copenhagen
      • Department of Biology
      Copenhagen, Capital Region, Denmark
  • 1994–2006
    • IT University of Copenhagen
      København, Capital Region, Denmark