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Limited suppression of photorespiration by 20th century atmospheric CO2 increase in trees worldwide
Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics. (Jürgen Schleucher)
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Forests are a key component of the global carbon and hydrological cycle and forest responses to  environmental  drivers  create  important  feedbacks  to  these  cycles.  Photosynthetic efficiency of most forest tree species is strongly limited by photorespiration, a side reaction using O2 instead of CO2 as substrate, leading to a carbon loss for the plant. Photorespiration occurs in all trees and is reduced under elevated CO2 concentrations and increased under elevated temperature. Because the CO2 concentration of the atmosphere has increased in past decades, long-lived trees may have benefited from reduced photorespiration, but the temperature increase would have been a compensating detriment; but direct quantification of long-term changes in metabolic fluxes is lacking. Realistic forecasting of responses of trees and forests to future CO2 and temperature demands quantifying the reduction of photorespiration.  In  twelve  tree  species  from  five  continents,  we  observe  that photorespiration has been reduced by the CO2 increase during the past century, but for most the reduction is smaller than predicted from plant responses in CO2 alone. Comparison with data from a combined CO2 and temperature manipulation experiment shows that the reduced response can be explained by increases in leaf temperatures, which might result directly from increased  air  temperatures  or  indirectly  from  reduced  transpirative  cooling.  These  data suggest that global warming has already inhibited plant fertilization by increasing CO2, and that biomass increases may have been smaller than deduced from measurements of the heavy carbon isotope 13C. Observation of this centennial metabolic shift in tree physiology worldwide provides new insights into forest-climate feedbacks and can be used to improve coupled climate-vegetation models.

National Category
Chemical Sciences Climate Research
URN: urn:nbn:se:umu:diva-97676OAI: diva2:775580
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

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