Time filter

Source Type

Wu Y.,University of Chinese Academy of Sciences | Tan H.,University of Chinese Academy of Sciences | Deng Y.,University of Chinese Academy of Sciences | Wu J.,University of Chinese Academy of Sciences | And 5 more authors.
Global Change Biology | Year: 2010

Characterizing the carbon turnover in terrestrial ecosystems is critical for understanding and predicting carbon dynamics in ecosystems. We used in situ 13C pulse labeling to track photosynthetic carbon fluxes from shoot to roots and to soil in a Kobresia humilis meadow on the Qinghai-Tibet Plateau. We found that about 36.7% of labeled carbon was translocated out from the shoots within the first 24 h after photosynthetic uptake. This is equivalent to 66.1% of total 13C moving out from the shoot during the 32-day chase period, indicating a rapid and large translocation of newly fixed carbon to belowground parts in these alpine plants. 58.7% of the assimilated 13C was transferred belowground. At the end of the chase phase, 30.9% was retained in living roots, 3.4% in dead roots, 17.2% lost as belowground respiration and 7.3% remained in the soil. In the four carbon pools (i.e., shoots, living roots, dead roots, and soil pools), living roots consistently had the highest proportion of 13C in the plant-soil system during the 32 days. Based on the 13C partitioning pattern and biomass production, we estimate a total of 4930 kg C ha-1 was allocated belowground during the vegetation growth season in this alpine meadow. Of this, roots accumulated 2868 kg C ha-1 and soils accumulated 613 kg C ha-1. This study suggests that carbon storage in belowground carbon pools plays the most important role in carbon cycles in the alpine meadow. © 2009 Blackwell Publishing Ltd.

Martel A.,Ghent University | Blooi M.,Ghent University | Blooi M.,Center for Research and Conservation | Adriaensen C.,Ghent University | And 27 more authors.
Science | Year: 2014

Emerging infectious diseases are reducing biodiversity on a global scale. Recently, the emergence of the chytrid fungus Batrachochytrium salamandrivorans resulted in rapid declines in populations of European fire salamanders. Here, we screened more than 5000 amphibians from across four continents and combined experimental assessment of pathogenicity with phylogenetic methods to estimate the threat that this infection poses to amphibian diversity. Results show that B. salamandrivorans is restricted to, but highly pathogenic for, salamanders and newts (Urodela). The pathogen likely originated and remained in coexistence with a clade of salamander hosts for millions of years in Asia. As a result of globalization and lack of biosecurity, it has recently been introduced into naïve European amphibian populations, where it is currently causing biodiversity loss. Copyright © 2014 by the American Association for the Advancement of Science; all rights reserved.

Saccon M.,York University | Busca R.,York University | Facca C.,York University | Huang L.,Environment Canada | And 5 more authors.
Atmospheric Measurement Techniques | Year: 2013

A method for the determination of the stable carbon isotopic composition of atmospheric nitrophenols in the gas and particulate phases is presented. It has been proposed to use the combination of concentration and isotope ratio measurements of precursor and product to test the applicability of results of laboratory studies to the atmosphere. Nitrophenols are suspected to be secondary products formed specifically from the photooxidation of volatile organic compounds. XAD-4TM resin was used as an adsorbent on quartz filters to sample ambient phenols using conventional high volume air samplers at York University in Toronto, Canada. Filters were extracted in acetonitrile, with a HPLC (high-performance liquid chromatography) clean-up step and a solid phase extraction step prior to derivatization with BSTFA (bis(trimethylsilyl) trifluoroacetamide). Concentration measurements were done with gas chromatography-mass spectrometry and gas chromatography-isotope ratio mass spectrometry was used for isotope ratio analysis.

The technique presented allows for atmospheric compound-specific isotopic composition measurements for five semi-volatile phenols with an estimated accuracy of 0.3-0.5‰ at atmospheric concentrations exceeding 0.1 ng m−3 while the detection limits for concentration measurements are in the pg m−3 range. Isotopic fractionation throughout the entire extraction procedure and analysis was proven to be below the precision of the isotope ratio measurements. The method was tested by conducting ambient measurements from September to December 2011. © 2013 Author(s).

Wu Y.,Ningbo University | Wu Y.,University of Chinese Academy of Sciences | Deng Y.,University of Chinese Academy of Sciences | Zhang J.,University of Chinese Academy of Sciences | And 5 more authors.
Ecological Research | Year: 2013

We used a minirhizotron system to investigate the influence of three major factors-root morphology, root depth, and season of root emergence-on root survivorship and longevity in a Kobresia humilis meadow on the Tibetan Plateau during the growing season of 2009. Root longevity was assessed by survival analysis, Kaplan-Meier analysis, and Cox proportional hazards regression. Root longevity was correlated positively with root diameter. A 17. 5 % decrease in the risk of mortality was associated with a 0. 1-mm increase in diameter. Roots distributed in the top 10 cm of the soil had significantly shorter longevities than roots at greater depths, with a 48 % decrease of mortality risk for each 10-cm increase in soil depth from the surface to 40 cm. Of all the factors examined, the season of root emergence had the strongest effect on root lifespan. Roots that emerged in May and June had shorter longevity than roots that emerged later in the year, and roots that emerged in September and October were more likely to survive over winter. Our findings indicated that life-history traits of roots in K. humilis meadows are highly heterogeneous, and this heterogeneity should be considered when modeling the contribution of roots to carbon and nitrogen fluxes in this type of meadow ecosystem. Moreover, temporal, spatial, and compositional variations in root longevity must be considered. © 2013 The Ecological Society of Japan.

Fu P.Q.,CAS Institute of Atmospheric Physics | Fu P.Q.,Hokkaido University | Kawamura K.,Hokkaido University | Cheng Y.F.,Max Planck Institute for Chemistry | And 4 more authors.
Atmospheric Chemistry and Physics | Year: 2014

Atmospheric aerosol samples were collected by aircraft at low to middle altitudes (0.8-3.5 km a.g.l.) over central East to West China during summer 2003 and spring 2004. The samples were analyzed for polar organic compounds using a technique of solvent extraction/BSTFA derivatization/gas chromatography-mass spectrometry. Biogenic secondary organic aerosol (SOA) tracers from the oxidation of isoprene were found to be more abundant in summer (3.3-138 ng m-3, mean 39 ng m-3) than in spring (3.2-42 ng m -3, 15 ng m-3), while α/β-pinene and β-caryophyllene SOA tracers showed similar abundances between these two seasons. A strong positive correlation (R2 Combining double low line 0.83) between levoglucosan and β-caryophyllinic acid was found in the spring samples vs. a weak correlation (R2 Combining double low line 0.17) in the summer samples, implying substantial contributions from biomass burning to the β-caryophyllinic acid production in spring. Two organic nitrogen species (oxamic acid and carbamide) were detected in the aircraft aerosol samples, and their concentrations were comparable to those of biogenic SOA tracers. Most of the primary organic aerosol (POA) and SOA tracers were less abundant at higher altitudes, suggesting they are of ground surface origin, either being directly emitted from anthropogenic/natural sources on the ground surface, or rapidly formed through photooxidation of their precursors emitted from the ground surface and then diluted during uplifting into the troposphere. This study demonstrates that primary biological aerosols, biogenic SOA, and organic nitrogen species are important components of organic aerosols in the troposphere over central China during warm seasons. © Author(s) 2014.

Discover hidden collaborations