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Hydrogen exchange during cellulose synthesis distinguishes climatic and biochemical isotope fractionations in tree rings.
Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics.
Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics.
2006 (English)In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 172, no 3, 490-499 p.Article in journal (Refereed) 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.

Place, publisher, year, edition, pages
2006. Vol. 172, no 3, 490-499 p.
Keyword [en]
Cellulose/*biosynthesis, Climate, Deuterium/metabolism, Hydrogen/chemistry/*metabolism, Picea/*metabolism, Plant Leaves/chemistry, Quercus/*metabolism, Soil/analysis, Water/analysis
Identifiers
URN: urn:nbn:se:umu:diva-6613DOI: 10.1111/j.1469-8137.2006.01843.xPubMedID: 17083679OAI: oai:DiVA.org:umu-6613DiVA: diva2:146282
Available from: 2007-12-16 Created: 2007-12-16 Last updated: 2015-03-18Bibliographically approved
In thesis
1. Monitoring climate and plant physiology using deuterium isotopomers of carbohydrates
Open this publication in new window or tab >>Monitoring climate and plant physiology using deuterium isotopomers of carbohydrates
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
Umeå: Fysiologisk botanik, 2007. 40 p.
Keyword
Climate reconstruction, deuterium, elevated CO2, isotopomer, nuclear magnetic resonance, photorespiration, tree-ring cellulose.
National Category
Botany
Identifiers
urn:nbn:se:umu:diva-1042 (URN)978-91-7264-281-2 (ISBN)
Public defence
2007-04-10, KB3A9, KBC Huset, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2007-03-15 Created: 2007-03-15 Last updated: 2009-08-26Bibliographically approved
2. Deuterium isotopomers as a tool in environmental research
Open this publication in new window or tab >>Deuterium isotopomers as a tool in environmental research
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Umeå: Medicinsk kemi och biofysik, 2006. 45 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1070
Keyword
deuterium, NMR, isotopomers, CO2 response, climate reconstruction, persistent pollutants, stable isotopes
National Category
Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-938 (URN)91-7264218-1 (ISBN)
Public defence
2006-12-08, KB3A9, Kemi Huset, Umeå University, Umeå, 13:30 (English)
Opponent
Supervisors
Note
Betson, Tatiana RAvailable from: 2006-11-20 Created: 2006-11-20 Last updated: 2009-09-30Bibliographically approved

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Schleucher, Jürgen

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