| 1. |
- Walker, Anthony P., et al.
(författare)
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Integrating the evidence for a terrestrial carbon sink caused by increasing atmospheric CO2
- 2021
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Ingår i: New Phytologist. - : John Wiley & Sons. - 0028-646X .- 1469-8137. ; 229:5, s. 2413-2445
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Tidskriftsartikel (refereegranskat)abstract
- Atmospheric carbon dioxide concentration ([CO2]) is increasing, which increases leaf‐scale photosynthesis and intrinsic water‐use efficiency. These direct responses have the potential to increase plant growth, vegetation biomass, and soil organic matter; transferring carbon from the atmosphere into terrestrial ecosystems (a carbon sink). A substantial global terrestrial carbon sink would slow the rate of [CO2] increase and thus climate change. However, ecosystem CO2 responses are complex or confounded by concurrent changes in multiple agents of global change and evidence for a [CO2]‐driven terrestrial carbon sink can appear contradictory. Here we synthesize theory and broad, multidisciplinary evidence for the effects of increasing [CO2] (iCO2) on the global terrestrial carbon sink. Evidence suggests a substantial increase in global photosynthesis since pre‐industrial times. Established theory, supported by experiments, indicates that iCO2 is likely responsible for about half of the increase. Global carbon budgeting, atmospheric data, and forest inventories indicate a historical carbon sink, and these apparent iCO2 responses are high in comparison to experiments and predictions from theory. Plant mortality and soil carbon iCO2 responses are highly uncertain. In conclusion, a range of evidence supports a positive terrestrial carbon sink in response to iCO2, albeit with uncertain magnitude and strong suggestion of a role for additional agents of global change.
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| 2. |
- Aguilar, Ximena, 1978-, et al.
(författare)
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Interaction Studies of the Human and Arabidopsis thaliana Med25-ACID Proteins with the Herpes Simplex Virus VP16-and Plant-Specific Dreb2a Transcription Factors
- 2014
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9:5, s. e98575-
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Tidskriftsartikel (refereegranskat)abstract
- Mediator is an evolutionary conserved multi-protein complex present in all eukaryotes. It functions as a transcriptional coregulator by conveying signals from activators and repressors to the RNA polymerase II transcription machinery. The Arabidopsis thaliana Med25 (aMed25) ACtivation Interaction Domain (ACID) interacts with the Dreb2a activator which is involved in plant stress response pathways, while Human Med25-ACID (hMed25) interacts with the herpes simplex virus VP16 activator. Despite low sequence similarity, hMed25-ACID also interacts with the plant-specific Dreb2a transcriptional activator protein. We have used GST pull-down-, surface plasmon resonance-, isothermal titration calorimetry and NMR chemical shift experiments to characterize interactions between Dreb2a and VP16, with the hMed25 and aMed25-ACIDs. We found that VP16 interacts with aMed25-ACID with similar affinity as with hMed25-ACID and that the binding surface on aMed25-ACID overlaps with the binding site for Dreb2a. We also show that the Dreb2a interaction region in hMed25-ACID overlaps with the earlier reported VP16 binding site. In addition, we show that hMed25-ACID/Dreb2a and aMed25-ACID/Dreb2a display similar binding affinities but different binding energetics. Our results therefore indicate that interaction between transcriptional regulators and their target proteins in Mediator are less dependent on the primary sequences in the interaction domains but that these domains fold into similar structures upon interaction.
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| 3. |
- Augusti, Angela, et al.
(författare)
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Deriving correlated climate and physiological signals from deuterium isotopomers in tree rings
- 2008
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Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541 .- 1872-6836. ; 252:1-2, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- he deuterium (D) abundance of tree-ring cellulose archives past climatic conditions, but previous attempts to access this archive have led to conflicting results. Based on an overview of D fractionation mechanisms in plants, we explain why past measurements of D abundance yield unreliable paleo signals. Our data show that variation in D abundance among the C–H groups (isotopomer variation) of tree-ring cellulose is generally greater than variation in D abundance due to climatic influences. A comparison of the D isotopomer abundances of soluble sugars of annual plants and of trees, and of tree-ring cellulose shows that an “isotopomer pattern” of the C3 photosynthetic pathway is transmitted from soluble sugars to tree-ring cellulose. Differences in this pattern between oaks and conifers appear to be related to differences in metabolism. Furthermore, the patterns are modified by hydrogen isotope exchange between C–H groups and source water during cellulose synthesis. Based on these results, we propose a strategy to simultaneously reconstruct climate signals and signals related to tree physiology from D isotopomers of tree rings. Combination of climate signals and physiological signals may allow the detection of century-time-scale adaptations of trees to past environmental change, and help to forecast future adaptations.
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| 4. |
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| 5. |
- Augusti, Angela, et al.
(författare)
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Hydrogen exchange during cellulose synthesis distinguishes climatic and biochemical isotope fractionations in tree rings.
- 2006
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Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 172:3, s. 490-499
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Tidskriftsartikel (refereegranskat)abstract
- • The abundance of the hydrogen isotope deuterium (D) in tree rings is an attractive record of climate; however, use of this record has proved difficult so far, presumably because climatic and physiological influences on D abundance are difficult to distinguish.• Using D labelling, we created a D gradient in trees. Leaf soluble sugars of relatively low D abundance entered cellulose synthesis in stems containing strongly D-labelled water. We used nuclear magnetic resonance (NMR) spectroscopy to quantify D in the C-H groups of leaf glucose and of tree-ring cellulose.• Ratios of D abundances of individual C-H groups of leaf glucose depended only weakly on leaf D labelling, indicating that the D abundance pattern was determined by physiological influences. The D abundance pattern of tree-ring cellulose revealed C-H groups that exchanged strongly (C(2)-H) or weakly (C(6)-H2) with water during cellulose synthesis.• We propose that strongly exchanging C-H groups of tree-ring cellulose adopt a climate signal stemming from the D abundance of source water. C-H groups that exchange weakly retain their D abundance established in leaf glucose, which reflects physiological influences. Combining both types of groups may allow simultaneous reconstruction of climate and physiology from tree rings.
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| 6. |
- Augusti, Angela, 1968-
(författare)
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Monitoring climate and plant physiology using deuterium isotopomers of carbohydrates
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Climate is changing and it is certain that this change is due to human activities. Atmospheric greenhouse gases have been rising in an unprecedented way during the last two centuries, although the land biosphere has dampened their increase by absorbing CO2 emitted by anthropogenic activities. However, it is unclear if this will continue in the future. This uncertainty makes it difficult to predict future climate changes and to determine how much greenhouse gas emissions must be reduced to protect climate. To understand the future role of plants in limiting the atmospheric CO2 level, the effect of increasing CO2 on plant photosynthesis and productivity has been studied. However, studies on trees showed contradictory results, which depended on the duration of the experiment. This revealed that an initial strong CO2 fertilization may be a transient response that disappears after a few years. Because climate changes over centuries, we must explore the response of vegetation to increasing CO2 on this time scale. Studying tree rings is a good alternative to impractical decade-long experiments, because trees have experienced the CO2 increase during the last 200 years and may already have responded to it. This thesis shows that the intramolecular distribution of the stable hydrogen isotope deuterium (deuterium isotopomer distribution, DID) of tree rings is a reliable tool to study long-term plant-climate adaptations. The premise for this is that the deuterium abundance in tree rings depends on environmental as well as physiological factors. Using newly developed methodology for DID measurements, the influences of both factors can be separated. Applied to tree rings, separating both factors opens a strategy for simultaneous reconstruction of climate and of physiological responses. The results presented show that DIDs are influenced by kinetic isotope effects of enzymes, allowing studies of metabolic regulation. We show that the abundances of specific D isotopomers in tree-ring cellulose indeed allow identifying environmental and physiological factors. For example, the D2 isotopomer is mostly influenced by environment, its abundance should allow better reconstruction of past temperature. On the other hand, the abundance ratio of two isotopomers (D6R and D6S) depends on atmospheric CO2, and might serve as a measure of the efficiency of photosynthesis (ratio of photorespiration to assimilation). The presence of this dependence in all species tested and in tree-ring cellulose allows studying adaptations of plants to increasing CO2 on long time scales, using tree-ring series or other remnant plant material.
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| 7. |
- Augusti, Angela, et al.
(författare)
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The ins and outs of stable isotopes in plants.
- 2007
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Ingår i: New Phytologist. - Oxford : Blackwell Scientific Publications Ltd. - 0028-646X .- 1469-8137. ; 174:3, s. 473-475
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Tidskriftsartikel (refereegranskat)
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| 8. |
- Baskaran, Preetisri, et al.
(författare)
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Nitrogen dynamics of decomposing Scots pine needle litter depends on colonizing fungal species
- 2019
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Ingår i: FEMS Microbiology Ecology. - : Oxford University Press. - 0168-6496 .- 1574-6941. ; 95:6
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Tidskriftsartikel (refereegranskat)abstract
- In boreal ecosystems plant production is often limited by low availability of nitrogen. Nitrogen retention in below-ground organic pools plays an important role in restricting recirculation to plants and thereby hampers forest production. Saprotrophic fungi are commonly assigned to different decomposer strategies, but how these relate to nitrogen cycling remains to be understood. Decomposition of Scots pine needle litter was studied in axenic microcosms with the ligninolytic litter decomposing basidiomycete Gymnopus androsaceus or the stress tolerant ascomycete Chalara longipes. Changes in chemical composition were followed by 13C CP/MAS NMR spectroscopy and nitrogen dynamics was assessed by the addition of a 15N tracer. Decomposition by C. longipes resulted in nitrogen retention in non-hydrolysable organic matter, enriched in aromatic and alkylic compounds, whereas the ligninolytic G. androsaceus was able to access this pool, counteracting nitrogen retention. Our observations suggest that differences in decomposing strategies between fungal species play an important role in regulating nitrogen retention and release during litter decomposition, implying that fungal community composition may impact nitrogen cycling at the ecosystem level.
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| 9. |
- Betson, Tatiana, 1975-
(författare)
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Deuterium isotopomers as a tool in environmental research
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes the development and the use of quantitative deuterium Nuclear Magnetic Resonance spectroscopy (NMR) as a tool in two areas of environmental research: the study of long term climate-plant interactions and the source tracking of persistent organic pollutant. Long-term interactions between plants and climate will influence climate change during this century and beyond, but cannot be studied in manipulative experiments. We propose that long tree rings series can serve as records for tracking such interactions during past centuries. The abundance of the stable hydrogen isotope deuterium (D) is influenced by physical and biochemical isotope fractionations. Because the overlapping effects of these fractionations are not understood, studies of the D abundance of tree rings led to conflicting results. We hypothesized that both types of fractionations can be separated if the D abundance of individual C-H groups of metabolites can be measured, that is if individual D isotopomers are quantified. The first paper describes a technique for quantification of D isotopomers in tree-ring cellulose by NMR. The technique showed that the D isotopomers distribution (DID) was non-random. Therefore, the abundance of each isotopomer potentially contains individual information which suggests an explanation for the conflicting results obtained by measuring the overall D abundance (dD). In the second paper, this technique was used to study hydrogen isotope exchange during cellulose synthesis in tree rings. This revealed that some C-H positions exchange strongly with xylem water, while others do not. This means that the exchanging C-H positions should acquire the D abundance of source water, which is determined by physical fractionations, while non-exchanging C-H positions of tree-ring cellulose should retain biochemical fractionations from the leaf level. Therefore, the abundance of the corresponding D isotopomers should contain information about climate and physiology. When analysing tree-ring series, the DIDs should reflect information about temperature, transpiration and regulation of photosynthesis. In the third paper, we showed that CO2 concentration during photosynthesis determines a specific abundance ratio of D isotopomers. This dependence was found in metabolites of annual plants, and in tree-ring cellulose. This result shows that D isotopomers of tree-ring series may be used to detect long-term CO2 fertilisation effects. This information is essential to forecast adaptations of plants to increasing CO2 concentrations on time scales of centuries. In the fourth paper, the source of persistent organic pollutants in the environment was tracked using DID measurements. The dD values of two compounds of related structures were not enough to show indisputably that they did not originate from the same source. However, the DIDs of the common part between the two compounds proved that they did not originate from the same source. These results underline the superior discriminatory power of DIDs, compared to dD measurements. The versatility of DID measurements makes them a precious tool in addressing questions that can not be answered by dD measurements.
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| 10. |
- Betson, Tatiana R, et al.
(författare)
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Quantification of deuterium isotopomers of tree-ring cellulose using nuclear magnetic resonance.
- 2006
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 78:24, s. 8406-8411
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Tidskriftsartikel (refereegranskat)abstract
- Stable isotopes in tree rings are important tools for reconstruction of past climate. Deuterium (D) is of particular interest since it may contain climate signals and report on tree physiology. Measurements of the D/H ratio of tree-ring cellulose have proven difficult to interpret, presumably because the D/H ratio of the whole molecule blends the abundances of the seven D isotopomers of cellulose. Here we present a method to measure the abundance of the D isotopomers of tree-ring cellulose by nuclear magnetic resonance spectroscopy (NMR). The method transforms tree-ring cellulose into a glucose derivative that gives highly resolved, quantifiable deuterium NMR spectra. General guidelines for measurement of D isotopomers by NMR are described. The transformation was optimized for yield and did not alter the original D isotopomer abundances, thus, conserving the original signals recorded in wood cellulose. In the tree-ring samples tested, the abundances of D isotopomers varied by approximately ±10% (2% standard error). This large variability can only be caused by biochemistry processes and shows that more information is present in D isotopomer abundances, compared to the D/H ratio. Therefore, measurements of the D isotopomer distribution of tree rings may be used to obtain information on long-term adaptations to environmental changes and past climate change.
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