Change search
ReferencesLink to record
Permanent link

Direct link
Quantification of a metabolic shift towards photosynthesisin C3 plants driven by 20th-century CO2 rise
Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics. (Jürgen Schleucher)
Show others and affiliations
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Terrestrial vegetation currently absorbs approximately a third of the annual anthropogenic CO2 emissions, mitigating the rise of atmospheric CO2. However,terrestrial net primary production is highly sensitive to atmospheric [CO2] and associated climatic changes. In C3-plants, which dominate terrestrial vegetation, netphotosynthesis depends on the ratio between gross photosynthesis and photorespiration, which strongly depends on [CO2]. However, our knowledge of feedbacks betweenterrestrial biomes and increasing atmospheric [CO2] is nearly entirely based on atmospheric inversion models and manipulation experiments, which do not reveal physiological mechanisms or are limited in duration and to step increases in [CO2]. By applying novel NMR (Nuclear Magnetic Resonance) spectroscopy methodology we examine isotopomer ratios of plant carbohydrates to probe shifts in the photosynthesis/photorespiration ratio in C3 plants over more than a century. Using herbarium samples of natural vascular plant species, crops and a Sphagnum species, we detect a consistent 35% increase in the 2photosynthesis/photorespiration ratio in responseto the ~100 ppm CO2 increase between approximately 1900 and 2013, with no evidencefor feedback regulation by the plants. Our data provide direct quantitative information on the “CO2 fertilization effect” over century time scales, thus addressing a major uncertainty in Earth system models, enabling improved predictions of the future [CO2] sink strength of terrestrial ecosystems. Further, relating the detected metabolic shift in crop plants to historic yield trends indicates that only a fraction of the increased net photosynthesis has translated into increased yield. Our results also demonstrate that archives of plant material contain metabolic information embedded in their isotopomer ratios covering centuries, bridging a fundamental gap between experimental plant science and paleoenvironmental studies.

National Category
Chemical Sciences
URN: urn:nbn:se:umu:diva-97675OAI: diva2:775578
Available from: 2015-01-03 Created: 2015-01-03 Last updated: 2015-01-15Bibliographically approved
In thesis
1. NMR studies of metabolites and xenobiotics: From time-points to long-term metabolic regulation
Open this publication in new window or tab >>NMR studies of metabolites and xenobiotics: From time-points to long-term metabolic regulation
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Chemical species carry information in two dimensions, in their concentrations and their isotopic signatures. The concentrations of metabolites or synthetic compounds describe the composition of a chemical or biological system, while isotopic signatures describe processes in the system by their reaction pathways, regulation, and responses to external stimuli. Stable isotopes are unique tracers of these processes because their natural abundances are modulated by isotope effects occurring in physical processes as well as in chemical reactions. Nuclear magnetic resonance (NMR) spectroscopy is a prime technique not only for identification and quantification of small molecules in complex systems but also for measuring intramolecular distribution of stable isotopes in metabolites and other small molecules. In this thesis, we use quantitative NMR in three fields: in food science, environmental pollutant tracing, and plant-climate science.

The phospholipid (PL) composition of food samples is of high interest because of their nutritional value and technological properties. However, the analysis of PLs is difficult as they constitute only a small fraction of the total lipid contents in foods. Here, we developed a method to identify PLs and determine their composition in food samples, by combining a liquid-liquid extraction approach for enriching PLs, with specialized 31P,1H-COSY NMR experiments to identify and quantify PLs.

Wide-spread pollution with synthetic compounds threatens the environment and human health. However, the fate of pollutants in the environment is often poorly understood. Using quantitative deuterium NMR spectroscopy, we showed for the nitrosamine NDMA and the pesticide DDT how intramolecular distributions (isotopomer patterns) of the heavy hydrogen isotope deuterium reveal mechanistic insight into transformation pathways of pollutants and organic compounds in general. Intramolecular isotope distributions can be used to trace a pollutant’s origin, to understand its environmental transformation pathways and to evaluate remediation approaches.

The atmospheric CO2 concentration ([CO2]) is currently rising at an unprecedented rate and plant responses to this increase in [CO2] influence the global carbon cycle and will determine future plant productivity. To investigate long-term plant responses, we developed a method to elucidate metabolic fluxes from intramolecular deuterium distributions of metabolites that can be extracted from historic plant material. We show that the intramolecular deuterium distribution of plant glucose depends on growth [CO2] and reflects the magnitude of photorespiration, an important side reaction of photosynthesis. In historic plant samples, we observe that photorespiration decreased in annual crop plants and natural vegetation over the past century, with no observable acclimation, implying that photosynthesis increased. In tree-ring samples from all continents covering the past 60 – 700 years, we detected a significantly smaller decrease in photorespiration than expected. We conclude that the expected “CO2 fertilization” has occurred but was significantly less pronounced in trees, due to opposing effects.

The presented applications show that intramolecular isotope distributions not only provide information about the origin and turnover of compounds but also about metabolic regulation. By extracting isotope distributions from archives of plant material, metabolic information can be obtained retrospectively, which allows studies over decades to millennia, timescales that are inaccessible with manipulation experiments.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2015. 54 p.
Umeå University medical dissertations, ISSN 0346-6612 ; 1691
NMR spectroscopy, isotopomer, phospholipid, persistent organic pollutant, CO2 fertilization, photorespiration
National Category
Biophysics Chemical Sciences
urn:nbn:se:umu:diva-97684 (URN)978-01-7601-195-9 (ISBN)
Public defence
2015-01-23, KB3A9, 10:00 (English)
Available from: 2015-01-07 Created: 2015-01-03 Last updated: 2015-05-19Bibliographically approved

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Ehlers, Ina
By organisation
Department of Medical Biochemistry and Biophysics
Chemical Sciences

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Total: 227 hits
ReferencesLink to record
Permanent link

Direct link