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Monitoring climate and plant physiology using deuterium isotopomers of carbohydrates
Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysiologisk botanik.
2007 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

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.

Abstract [sv]

Klimatet förändras och det är numera allmänt vedertaget att detta beror på människans aktiviteter. Halten av växthusgaser har stigit onormalt mycket under de senaste två århundradena och detta beror i största del på människans användning av fossila bränslen. Landbiosfären har hittills haft en buffrande effekt på klimatförändringen eftersom den tar upp och lagrar mycket av växthusgasen CO2. Det är dock osäkert om, och i så fall hur länge, denna effekt kvarstår. Detta gör det mycket svårt att förutsäga framtida klimatförändringar, och därmed hur mycket utsläppen av växthusgaser måste reduceras för att skydda klimatet.

För att förstå växternas framtida förmåga att begränsa halten atmosfäriskt CO2 har man studerat effekten av förhöjda halter av CO2 på växters fotosyntes och produktivitet. Resultaten av dessa försök varierar i stor omfattning. Studier på träd odlade under höga halter CO2 indikerar att den initiala ökningen av en trädets produktivitet kan vara en temporär effekt som försvinner redan efter några år. Eftersom klimatförändringen sker under århundraden, måste även växternas anpassningar på förhöjd CO2 halt utforskas på denna tidsskala, men experiment som skulle ta tiotals år är opraktiska att utföra. Trädringar är ett bra sätt att studera sådana anpassningar, eftersom träd redan har upplevt de senaste två hundra årens ökning av koldioxid och dess trädringar därför kan innehålla information om en respons som redan skett.

Denna avhandling visar att den intramolekylära fördelningen av den stabila väteisotopen deuterium i trädringar är en tillförlitlig metod för att studera växters anpassningsförmåga till långsiktiga klimatförändringar. Antagandet bakom denna strategi är att isotopfördelningen i trädringar beror på faktorer både från miljön och växtens fysiologi. Om båda faktorerna skulle kunna utvinnas från trädringar, skulle detta öppna en helt ny väg för parallell rekonstruktion av klimatet och växters anpassning till det. Avhandlingen presenterar den första tekniken för att mäta isotopfördelningen av deuterium i växtglukos. Resultaten visar att deuteriumfördelningen hos växtglukos påverkas av enzymers isotopeffekter, vilket möjliggör att regleringen av växternas metabolism kan kartläggas. I avhandlingen bevisas att halten deuterium i skilda intramolekylära positioner (isotopomerer) av glukos från trädringcellulosa bestäms av miljöfaktorer respektive trädets fysiologi. T.ex. påverkas deuteriumhalten i position 2 (D2 isotopomer) av glukosmolekylen huvudsakligen av miljön, vilket kan användas för att förbättra temperaturrekonstruktioner från trädringar. Å andra sidan är kvoten deuterium mellan två andra positioner (D6R och D6S) relaterat till halten atmosfäriskt koldioxid, och kvoten skulle kunna användas som mått för fotosyntesens effektivitet, dvs. förhållandet mellan fotorespiration och fotosyntes. Närvaron av denna relation i trädringar och annat växtmaterial i alla de växter vi hittills studerat, öppnar en helt ny möjlighet att studera växters anpassning till den ökande mängden CO2 i atmosfären under århundraden.

sted, utgiver, år, opplag, sider
Umeå: Fysiologisk botanik , 2007. , s. 40
Emneord [en]
Climate reconstruction, deuterium, elevated CO2, isotopomer, nuclear magnetic resonance, photorespiration, tree-ring cellulose.
HSV kategori
Identifikatorer
URN: urn:nbn:se:umu:diva-1042ISBN: 978-91-7264-281-2 (tryckt)OAI: oai:DiVA.org:umu-1042DiVA, id: diva2:140028
Disputas
2007-04-10, KB3A9, KBC Huset, Umeå, 13:00 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2007-03-15 Laget: 2007-03-15 Sist oppdatert: 2009-08-26bibliografisk kontrollert
Delarbeid
1. Quantification of deuterium isotopomers of tree-ring cellulose using nuclear magnetic resonance.
Åpne denne publikasjonen i ny fane eller vindu >>Quantification of deuterium isotopomers of tree-ring cellulose using nuclear magnetic resonance.
2006 (engelsk)Inngår i: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 78, nr 24, s. 8406-8411Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

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.

Emneord
Cellulose/*analysis/chemistry, Climate, Deuterium/*chemistry, Ecosystem, Environmental Monitoring, Glucose/analogs & derivatives/*analysis, Isotope Labeling, Magnetic Resonance Spectroscopy/*methods, Trees/chemistry/*growth & development
Identifikatorer
urn:nbn:se:umu:diva-6612 (URN)10.1021/ac061050a (DOI)17165833 (PubMedID)
Tilgjengelig fra: 2007-12-16 Laget: 2007-12-16 Sist oppdatert: 2018-06-09bibliografisk kontrollert
2. Hydrogen exchange during cellulose synthesis distinguishes climatic and biochemical isotope fractionations in tree rings.
Åpne denne publikasjonen i ny fane eller vindu >>Hydrogen exchange during cellulose synthesis distinguishes climatic and biochemical isotope fractionations in tree rings.
2006 (engelsk)Inngår i: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 172, nr 3, s. 490-499Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

• 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.

Emneord
Cellulose/*biosynthesis, Climate, Deuterium/metabolism, Hydrogen/chemistry/*metabolism, Picea/*metabolism, Plant Leaves/chemistry, Quercus/*metabolism, Soil/analysis, Water/analysis
Identifikatorer
urn:nbn:se:umu:diva-6613 (URN)10.1111/j.1469-8137.2006.01843.x (DOI)17083679 (PubMedID)
Tilgjengelig fra: 2007-12-16 Laget: 2007-12-16 Sist oppdatert: 2018-06-09bibliografisk kontrollert
3. Deriving correlated climate and physiological signals from deuterium isotopomers in tree rings
Åpne denne publikasjonen i ny fane eller vindu >>Deriving correlated climate and physiological signals from deuterium isotopomers in tree rings
2008 (engelsk)Inngår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 252, nr 1-2, s. 1-8Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

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.

Emneord
Isotopomer, NMR, Climate reconstruction, Stable isotope, Biochemical pathway, Metabolic control
Identifikatorer
urn:nbn:se:umu:diva-9645 (URN)10.1016/j.chemgeo.2008.01.011 (DOI)
Tilgjengelig fra: 2008-05-07 Laget: 2008-05-07 Sist oppdatert: 2018-06-09bibliografisk kontrollert
4. Deuterium isotopomers record a CO2 response of plants in leaves and tree rings
Åpne denne publikasjonen i ny fane eller vindu >>Deuterium isotopomers record a CO2 response of plants in leaves and tree rings
(engelsk)Manuskript (Annet (populærvitenskap, debatt, mm))
Identifikatorer
urn:nbn:se:umu:diva-2165 (URN)
Tilgjengelig fra: 2007-03-15 Laget: 2007-03-15 Sist oppdatert: 2018-06-09bibliografisk kontrollert

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