113 research outputs found
Mycorrhizal type dictates soil microbial diversity and function and the integrated root-microbial response to water stress in temperate forests
Our understanding of the mechanisms that control the magnitude of the temperate forest carbon (C) sink and its response to global change remain uncertain. Much of this uncertainty lies in the extent to which differences between tree species in their mycorrhizal symbionts and corresponding nutrient acquisition strategies control the activity of soil microbes that mobilize nutrients and decompose soil organic matter. ECM trees allocate substantial amounts of C to ECM fungi and rhizosphere microbes to mine soil organic matter for nutrients. By contrast, AM trees invest less C belowground and rely on AM fungi to scavenge for nutrients. While these strategies have been shown to lead to differences in microbial function at the plot scale, there has been limited research that has investigated how these strategies shape microbial diversity or how the resulting differences in diversity impact function at the microbial scale. Moreover, the ability of these nutrient acquisition strategies to shape microbial communities likely controls ecosystem responses to global change. Thus, my research questions are: (1) Does microbial diversity drive function and the resulting products of decomposition in temperate forest soils? (2) To what extent do temperate forest trees shift their investment of C above vs. belowground under water stress? (3) How do plant-microbial interactions impact decomposition in temperate forests under water stress? For question 1, I examined the extent to which differences between AM and ECM trees in their nutrient acquisition strategies alter microbial diversity and function in a ~120-year-old forest in Tomâs Run Natural Area, West Virginia. I sampled soils in plots dominated by either AM or ECM trees and assayed microbial diversity and function through quantitative stable isotope probing and metabolomic analysis. I found that AM soils had greater microbial diversity than ECM soils. This difference in diversity led to more flexible decomposition pathways and more products that could form more stable soil C in AM than ECM soils. For question 2, I built a throughfall exclusion experiment at Tomâs Run in AM and ECM dominated plots and measured the effect of water stress on C allocation to above- vs. belowground processes. In response to the treatment, I found that ECM trees maintained root biomass and mycorrhizal colonization, while AM trees increased investment in roots and mycorrhizae. This reflects the ability of ECM trees to leverage their already extensive nutrient acquisition infrastructure to enhance water uptake. By contrast, it was necessary for AM trees to upregulate investment belowground to ensure access to water. For question 3, I measured the response of microbial activity to the water stress treatment at Tomâs Run. I show that the treatment led to declines in soil respiration, nitrogen mineralization and oxidative enzyme activity in AM soil, which may be due to AM trees reducing root C transfers to the soil. In ECM soils, the treatment enhanced soil respiration, as well as rates of N mineralization and peroxidase activity in the rhizosphere soils, suggesting ECM roots provided optimal conditions to prime microbial activity. Collectively, these results provide evidence that differences between AM and ECM nutrient acquisition strategies led to divergent microbial diversity and function that can impact soil C storage and ecosystem responses to global change
Quantum Interaction : the Construction of Quantum Field defined as a Bilinear Form
We construct the solution of the quantum wave equation
as a bilinear form which can
be expanded over Wick polynomials of the free -field, and where
is defined as the normal ordered product with
respect to the free -field. The constructed solution is correctly defined
as a bilinear form on , where is a
dense linear subspace in the Fock space of the free -field. On
the diagonal Wick symbol of this bilinear form
satisfies the nonlinear classical wave equation.Comment: 32 pages, LaTe
Improved Conformal Mapping of the Borel Plane
The conformal mapping of the Borel plane can be utilized for the analytic
continuation of the Borel transform to the entire positive real semi-axis and
is thus helpful in the resummation of divergent perturbation series in quantum
field theory. We observe that the rate of convergence can be improved by the
application of Pad\'{e} approximants to the Borel transform expressed as a
function of the conformal variable, i.e. by a combination of the analytic
continuation via conformal mapping and a subsequent numerical approximation by
rational approximants. The method is primarily useful in those cases where the
leading (but not sub-leading) large-order asymptotics of the perturbative
coefficients are known.Comment: 6 pages, LaTeX, 2 tables; certain numerical examples adde
Bulk Scalar Stabilization of the Radion without Metric Back-Reaction in the Randall-Sundrum Model
Generalizations of the Randall-Sundrum model containing a bulk scalar field
interacting with the curvature through the general coupling are considered. We derive the general form of the effective 4D
potential for the spin-zero fields and show that in the mass matrix the radion
mixes with the Kaluza-Klein modes of the bulk scalar fluctuations. We
demonstrate that it is possible to choose a non-trivial background form
(where is the extra dimension coordinate) for the bulk scalar
field such that the exact Randall-Sundrum metric is preserved (i.e. such that
there is no back-reaction). We compute the mass matrix for the radion and the
KK modes of the excitations of the bulk scalar relative to the background
configuration and find that the resulting mass matrix implies a
non-zero value for the mass of the radion (identified as the state with the
lowest eigenvalue of the scalar mass matrix). We find that this mass is
suppressed relative to the Planck scale by the standard warp factor needed to
explain the hierarchy puzzle, implying that a mass \sim 1\tev is a natural
order of magnitude for the radion mass. The general considerations are
illustrated in the case of a model containing an interaction term.Comment: 22 pages, 3 figure
A Unified Conformal Model for Fundamental Interactions without Dynamical Higgs Field
A Higgsless model for strong, electro-weak and gravitational interactions is
proposed. This model is based on the local symmetry group SU(3)xSU(2)xU(1)xC
where C is the local conformal symmetry group. The natural minimal conformally
invariant form of total lagrangian is postulated. It contains all Standard
Model fields and gravitational interaction. Using the unitary gauge and the
conformal scale fixing conditions we can eliminate all four real components of
the Higgs doublet in this model. However the masses of vector mesons, leptons
and quarks are automatically generated and are given by the same formulas as in
the conventional Standard Model. The gravitational sector is analyzed and it is
shown that the model admits in the classical limit the Einsteinian form of
gravitational interactions. No figures.Comment: 25 pages, preprin
Experimental Constraints on the Neutrino Oscillations and a Simple Model of Three Flavour Mixing
A simple model of the neutrino mixing is considered, which contains only one
right-handed neutrino field, coupled via the mass term to the three usual
left-handed fields. This is a simplest model that allows for three-flavour
neutrino oscillations. The existing experimental limits on the neutrino
oscillations are used to obtain constraints on the two free mixing parameters
of the model. A specific sum rule relating the oscillation probabilities of
different flavours is derived.Comment: 10 pages, 3 figures in post script, Latex, IFT 2/9
On the role of power expansions in quantum field theory
Methods of summation of power series relevant to applications in quantum
theory are reviewed, with particular attention to expansions in powers of the
coupling constant and in inverse powers of an energy variable. Alternatives to
the Borel summation method are considered and their relevance to different
physical situations is discussed. Emphasis is placed on quantum chromodynamics.
Applications of the renormalon language to perturbation expansions (resummation
of bubble chains) in various QCD processes are reported and the importance of
observing the full renormalization-group invariance in predicting observables
is emphasized. News in applications of the Borel-plane formalism to
phenomenology are conveyed. The properties of the operator-product expansion
along different rays in the complex plane are examined and the problem is
studied how the remainder after subtraction of the first terms depends on
the distance from euclidean region. Estimates of the remainder are obtained and
their strong dependence on the nature of the discontinuity along the cut is
shown. Relevance of this subject to calculations of various QCD effects is
discussed.Comment: 50 pages, Latex, 1 Postscript figur
Study of shock waves generation, hot electron production and role of parametric instabilities in an intensity regime relevant for the shock ignition
We present experimental results at intensities relevant to Shock Ignition
obtained at the sub-ns Prague Asterix Laser System in 2012 . We studied shock waves
produced by laser-matter interaction in presence of a pre-plasma. We used a first beam at
1Ï (1315 nm) at 7 Ă 10 13 W/cm 2 to create a pre-plasma on the front side of the target and
a second at 3Ï (438 nm) at ⌠10 16 W/cm 2 to create the shock wave. Multilayer targets
composed of 25 (or 40 Όm) of plastic (doped with Cl), 5 Όm of Cu (for Kα diagnostics)
and 20 ÎŒm of Al for shock measurement were used. We used X-ray spectroscopy of Cl
to evaluate the plasma temperature, Kα imaging and spectroscopy to evaluate spatial and
spectral properties of the fast electrons and a streak camera for shock breakout measurements.
Parametric instabilities (Stimulated Raman Scattering, Stimulated Brillouin Scattering and
Two Plasmon Decay) were studied by collecting the back scattered light and analysing its
spectrum. Back scattered energy was measured with calorimeters. To evaluate the maximum
pressure reached in our experiment we performed hydro simulations with CHIC and DUED
codes. The maximum shock pressure generated in our experiment at the front side of the
target during laser-interaction is 90 Mbar. The conversion efficiency into hot electrons was
estimated to be of the order of ⌠0.1% and their mean energy in the order âŒ50 keV.
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distributio
Tall tales from de Sitter space II: Field theory dualities
We consider the evolution of massive scalar fields in (asymptotically) de
Sitter spacetimes of arbitrary dimension. Through the proposed dS/CFT
correspondence, our analysis points to the existence of new nonlocal dualities
for the Euclidean conformal field theory. A massless conformally coupled scalar
field provides an example where the analysis is easily explicitly extended to
'tall' background spacetimes.Comment: 31 pages, 2 figure
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Amazonian pollen assemblages reflect biogeographic gradients and forest cover
Aim Pollen assemblages are commonly used to reconstruct past climates yet have not yet been used to reconstruct past human activities, including deforestation. We aim to assess (i) how pollen assemblages vary across biogeographic and environmental gradients, (ii) the source area of pollen assemblages from lake sediment samples and (iii) which pollen taxa can best be used to quantify deforested landscapes. Location Amazonia. Taxon Plantae. Methods Pollen assemblages (N = 65) from mudâwater interface samples (representing modern conditions) of lake sediment cores were compared with modern gradients of temperature, precipitation and elevation. Pollen assemblages were also compared with localâscale estimates of forest cover at 1, 2, 5, 10, 20 and 40 km buffers around each lake.ResultsOver 250 pollen types were identified in the samples, and pollen assemblages were able to accurately differentiate biogeographic regions across the basin, corresponding with gradients in temperature and precipitation. Poaceae percentages were the best predictor of deforestation, and had a significant negative relationship with forest cover estimates. These relationships were strongest for the 1 km buffer area, weakening as buffer sizes increased.Main conclusionsThe diverse Amazonian pollen assemblages strongly reflect environmental gradients, and percentages of Poaceae best reflect localâscale variability in forest cover. Our results of modern pollenâlandscape relationships can be used to provide a foundation for quantitative reconstructions of climate and deforestation in Amazonia
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