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Jülich, Germany

Bessler H.,Humboldt University of Berlin | Oelmann Y.,University of Tubingen | Roscher C.,Helmholtz Center for Environmental Research | Buchmann N.,ETH Zurich | And 5 more authors.
Plant and Soil | Year: 2012

Aims: This study aimed to measure the effect of plant diversity on N uptake in grasslands and to assess the mechanisms contributing to diversity effects. Methods: Annual N uptake into above- and belowground organs and soil nitrate pools were measured in the Jena experiment on a floodplain soil with mixtures of 2-16 species and 1-4 functional groups, and monocultures. In mixtures, the deviation of measured data from data expected from monoculture performance was calculated to assess the contribution of complementarity/facilitation and selection. Results: N uptake varied from <1 to 45 g N m-2 yr-1, and was higher in grasslands with than without legumes. On average, N uptake was higher in mixtures (21 ± 1 g N m-2 yr-1) than monocultures (13 ± 1 g N m-2 yr-1), and increased with species richness in mixtures. However, compared to N uptake expected from biomass proportions of species in mixtures, N uptake of mixtures was only slightly higher and a significant surplus N uptake was confined to mixtures containing legumes and non-legumes. Conclusions: In our study, high N uptake of species rich mixtures was mainly due to dominance of productive species and facilitation by legumes whereas complementarity among non-legumes was of minor relevance. © 2012 Springer Science+Business Media B.V. Source

Phillips G.J.,Max Planck Institute for Chemistry | Tang M.J.,Max Planck Institute for Chemistry | Thieser J.,Max Planck Institute for Chemistry | Brickwedde B.,Max Planck Institute for Chemistry | And 4 more authors.
Geophysical Research Letters | Year: 2012

We present the first measurements of nitryl chloride (ClNO2) over continental Europe. Significant quantities of ClNO2, up to 800 pptv, were measured at a mountaintop field site in Hessen, southwest Germany. ClNO2 was detected during the majority of nights between the 15th August and 16th September 2011, its largest mixing ratios being associated with air masses influenced by sea salt and anthropogenic NOx emissions. ClNO2 persisted in measurable quantities until early afternoons on days with low photolysis frequencies. As a consequence, early morning production rates of Cl atoms could significantly exceed the production of OH via ozone photolysis, likely leading to increased O3 production. Copyright © 2012 by the American Geophysical Union. Source

He Y.,University of Bonn | Siemens J.,University of Bonn | Amelung W.,University of Bonn | Amelung W.,Forschungzentrum Julich GmbH | And 5 more authors.
Agriculture, Ecosystems and Environment | Year: 2015

Crop rotations encompassing flooded rice and an upland crop are commonly found in large parts of South and East Asia. However, also rice farmers in Southeast Asia increasingly switch from double-cropping paddy rice to one non-flooded crop-such as maize-in the dry season. We hypothesized that introducing maize (maize-paddy rice, M-MIX) into a double paddy rice (R-WET) cropping system will increase carbon (C) release from rice roots into the rhizosphere and the dissolved soil C pool. To test this hypothesis we assessed the kinetics of C release by the rice plants in a hydroponic greenhouse experiment, and used these data for interpreting their C release in field experiments using 13C pulse labeling of rice plants. In the greenhouse we observed that rice roots released 13C labeled dissolved organic carbon (DOC) for 21 days with a mean residence time (MRT) of 19 days after exposure to a 13CO2 pulse. The MRT of labeled dissolved inorganic carbon (DIC) released from rice roots was only 2 days. In the field 13CO2 pulse labeling increased the 13C excess of rhizosphere soil up to 0.7±0.2mg 13Ckg-1 in R-WET and 0.9±0.3mg kg-1 in M-MIX. The 13C signature of bulk soil remained unaffected. DOC concentrations in R-WET were significantly higher than in M-MIX during the mature grain stage of the rice plants. Nevertheless, the 13C excess in DOC transiently increased by only 0.5μgL-1 after labeling in 13cm depth in one of three lysimeters previously cropped with maize (M-MIX), while no labeled DOC was detected in 13cm depth of the R-WET lysimeters and in 60cm depth of both treatments. In contrast, the 13C excess of DIC increased by 42.4-93.1μgL-1 a few days after labeling with a MRT of 53-66 days in both treatments. Considering the results of the greenhouse experiment, this suggests a rapid mineralization of labeled rhizodeposits in the field and an effective transient storage of CO2 produced by respiration in soil water. © 2015 Elsevier B.V. Source

McConnell R.,Harvard University | Gabrielse G.,Harvard University | Kolthammer W.S.,Harvard University | Richerme P.,Harvard University | And 9 more authors.
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2016

Lasers are used to control the production of highly excited positronium atoms (Ps∗). The laser light excites Cs atoms to Rydberg states that have a large cross section for resonant charge-exchange collisions with cold trapped positrons. For each trial with 30 million trapped positrons, more than 700 000 of the created Ps∗ have trajectories near the axis of the apparatus, and are detected using Stark ionization. This number of Ps∗ is 500 times higher than realized in an earlier proof-of-principle demonstration (2004 Phys. Lett. B 597 257). A second charge exchange of these near-axis Ps∗ with trapped antiprotons could be used to produce cold antihydrogen, and this antihydrogen production is expected to be increased by a similar factor. © 2016 IOP Publishing Ltd. Source

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