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Sökning: WFRF:(Robertson Iain)

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1.
  • Campbell, Rochelle, et al. (författare)
  • BLUE INTENSITY IN PINUS SYLVESTRIS TREE RINGS : A MANUAL FOR A NEW PALAEOCLIMATE PROXY
  • 2011
  • Ingår i: TREE-RING RESEARCH. - : Tree-Ring Society. - 1536-1098. ; 67:2, s. 127-134
  • Tidskriftsartikel (refereegranskat)abstract
    • Minimum blue intensity is a reflected light imaging technique that provides an inexpensive, robust and reliable surrogate for maximum latewood density. In this application it was found that temperature reconstructions from resin-extracted samples of Pious sylvestris (L.) from Fennoscandia provide results equivalent to conventional x-ray densitometry. This paper describes the implementation of the blue intensity method using commercially available software and a flat-bed scanner. A calibration procedure is presented that permits results obtained by different laboratories, or using different scanners, to be compared. In addition, the use of carefully prepared and chemically treated 10-mm-diameter cores are explored; suggesting that it may not be necessary to produce thin laths with the rings aligned exactly perpendicular to the measurement surface.
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  • Ehlers, Ina, 1984-, et al. (författare)
  • Limited suppression of photorespiration by 20th century atmospheric CO2 increase in trees worldwide
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • 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.
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5.
  • Gagen, Mary, et al. (författare)
  • Cloud response to summer temperatures in Fennoscandia over the last thousand years
  • 2011
  • Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 38, s. L05701-
  • Tidskriftsartikel (refereegranskat)abstract
    • Cloud cover is one of the most important factors controlling the radiation balance of the Earth. The response of cloud cover to increasing global temperatures represents the largest uncertainty in model estimates of future climate because the cloud response to temperature is not well-constrained. Here we present the first regional reconstruction of summer sunshine over the past millennium, based on the stable carbon isotope ratios of pine treerings from Fennoscandia. Comparison with the regional temperature evolution reveals the Little Ice Age (LIA) to have been sunny, with cloudy conditions in the warmest periods of the Medieval at this site. A negative shortwave cloud feedback is indicated at high latitude. A millennial climate simulation suggests that regionally low temperatures during the LIA were mostly maintained by a weaker greenhouse effect due to lower humidity. Simulations of future climate that display a negative shortwave cloud feedback for high-latitudes are consistent with our proxy interpretation. Citation: Gagen, M., E. Zorita, D. McCarroll, G. H. F. Young, H. Grudd, R. Jalkanen, N. J. Loader, I. Robertson, and A. Kirchhefer (2011), Cloud response to summer temperatures in Fennoscandia over the last thousand years, Geophys. Res. Lett., 38, L05701, doi:10.1029/2010GL046216.
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6.
  • Kaislahti Tillman, Päivi, 1958-, et al. (författare)
  • Stable carbon and oxygen isotopes in Sphagnum fuscum peat from subarctic Canada : implications for palaeoclimate studies
  • 2010
  • Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541 .- 1872-6836. ; 270:1-4, s. 216-226
  • Tidskriftsartikel (refereegranskat)abstract
    • Stable carbon and oxygen isotope ratios in single plant components in Sphagnum peat have a good potential to reveal environmental changes in peat archives. Two peat profiles, covering the past ~6000 years, and a Sphagnum hummock from a discontinuous permafrost area in west central Canada were studied in order to evaluate the effect of decomposition rate on isotope records and to assess which plant components are most suitable for climate reconstructions. The stable isotope values from the most recently forming Sphagnum tissues were compared with observational climate data to study the impact of variations in temperature and precipitation on the peat isotopes. Our results show that there is high correlation between δ13C values in α-cellulose isolated from Sphagnum fuscum stems and summer temperatures, whereas δ18O in the plant tissues is controlled by several factors, such as summer precipitation, summer temperature and evaporation. According to our results, decomposition as derived from C/N values and colorimetry does not seem to affect the oxygen and carbon isotope values of α-cellulose from Sphagnum fuscum peat significantly. There is, however, a (quasi-) constant offset between the isotope values of branches and stems and between whole plant material and  α-cellulose, which makes it crucial to select single moss-fractions when past climate and environmental changes are to be derived from the isotope record.
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7.
  • Mccarroll, Danny, et al. (författare)
  • A critical evaluation of multi-proxy dendroclimatology in northern Finland
  • 2011
  • Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 26:1, s. 7-14
  • Tidskriftsartikel (refereegranskat)abstract
    • Twentieth-century summer (July-August) temperatures in northern Finland are reconstructed using ring widths, maximum density and stable carbon isotope ratios (delta(13)C) of Scots pine tree rings, and using combinations of these proxies. Verification is based on the coefficient of determination (r(2)), reduction of error (RE) and coefficient of efficiency (CE) statistics. Of the individual proxies, delta(13)C performs best, followed by maximum density. Combining delta(13)C and maximum density strengthens the climate signal but adding ring widths leads to little improvement. Blue intensity, an inexpensive alternative to X-ray densitometry, is shown to perform similarly. Multi-proxy reconstruction of summer temperatures from a single site produces strong correlations with gridded climate data over most of northern Fennoscandia. Since relatively few trees are required (<15) the approach could be applied to long sub-fossil chronologies where replication may be episodically low.
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8.
  • Rao, Komal Umashankar, et al. (författare)
  • A broad spectrum anti-bacterial peptide with an adjunct potential for tuberculosis chemotherapy
  • 2021
  • Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 11:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Alternative ways to prevent and treat infectious diseases are needed. Previously, we identified a fungal peptide, NZX, that was comparable to rifampicin in lowering M. tuberculosis load in a murine tuberculosis (TB) infection model. Here we assessed the potential synergy between this cationic host defence peptide (CHDP) and the current TB drugs and analysed its pharmacokinetics. We found additive effect of this peptide with isoniazid and ethambutol and confirmed these results with ethambutol in a murine TB-model. In vivo, the peptide remained stable in circulation and preserved lung structure better than ethambutol alone. Antibiotic resistance studies did not induce mutants with reduced susceptibility to the peptide. We further observed that this peptide was effective against nontuberculous mycobacteria (NTM), such as M. avium and M. abscessus, and several Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus. In conclusion, the presented data supports a role for this CHDP in the treatment of drug resistant organisms.
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9.
  • Saurer, Matthias, et al. (författare)
  • Spatial variability and temporal trends in water-use efficiency of European forests
  • 2014
  • Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 20:12, s. 3700-3712
  • Tidskriftsartikel (refereegranskat)abstract
    • The increasing carbon dioxide (CO2) concentration in the atmosphere in combination with climatic changes throughout the last century are likely to have had a profound effect on the physiology of trees: altering the carbon and water fluxes passing through the stomatal pores. However, the magnitude and spatial patterns of such changes in natural forests remain highly uncertain. Here, stable carbon isotope ratios from a network of 35 tree-ring sites located across Europe are investigated to determine the intrinsic water-use efficiency (iWUE), the ratio of photosynthesis to stomatal conductance from 1901 to 2000. The results were compared with simulations of a dynamic vegetation model (LPX-Bern 1.0) that integrates numerous ecosystem and land-atmosphere exchange processes in a theoretical framework. The spatial pattern of tree-ring derived iWUE of the investigated coniferous and deciduous species and the model results agreed significantly with a clear south-to-north gradient, as well as a general increase in iWUE over the 20th century. The magnitude of the iWUE increase was not spatially uniform, with the strongest increase observed and modelled for temperate forests in Central Europe, a region where summer soil-water availability decreased over the last century. We were able to demonstrate that the combined effects of increasing CO2 and climate change leading to soil drying have resulted in an accelerated increase in iWUE. These findings will help to reduce uncertainties in the land surface schemes of global climate models, where vegetation-climate feedbacks are currently still poorly constrained by observational data.
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10.
  • Treydte, Kerstin, et al. (författare)
  • Recent human-induced atmospheric drying across Europe unprecedented in the last 400 years
  • 2024
  • Ingår i: NATURE GEOSCIENCE. - 1752-0894 .- 1752-0908. ; 17
  • Tidskriftsartikel (refereegranskat)abstract
    • The vapor pressure deficit reflects the difference between how much moisture the atmosphere could and actually does hold, a factor that fundamentally affects evapotranspiration, ecosystem functioning, and vegetation carbon uptake. Its spatial variability and long-term trends under natural versus human-influenced climate are poorly known despite being essential for predicting future effects on natural ecosystems and human societies such as crop yield, wildfires, and health. Here we combine regionally distinct reconstructions of pre-industrial summer vapor pressure deficit variability from Europe's largest oxygen-isotope network of tree-ring cellulose with observational records and Earth system model simulations with and without human forcing included. We demonstrate that an intensification of atmospheric drying during the recent decades across different European target regions is unprecedented in a pre-industrial context and that it is attributed to human influence with more than 98% probability. The magnitude of this trend is largest in Western and Central Europe, the Alps and Pyrenees region, and the smallest in southern Fennoscandia. In view of the extreme drought and compound events of the recent years, further atmospheric drying poses an enhanced risk to vegetation, specifically in the densely populated areas of the European temperate lowlands. The atmosphere has dried across most regions of Europe in recent decades, a trend that can be attributed primarily to human impacts, according to tree ring records spanning 400 years and Earth system model simulations.
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