1,202 research outputs found
Genotypic variation in morphology and freezing resistance of Eucalyptus globulus seedlings subjected to drought hardening in nursery
Eucalyptus globulus Labill is one of the most planted species in
Chile, because of its fast growth and superior pulp qualities.
Nevertheless, the incidence of drought and frost damage immediately
after planting is frequent. The purpose of this work was to study the
effect of drought hardening on frost resistance and on variations in
morphological traits that may increase drought resistance at nursery
phase in four genotypes of E. globulus Labill. Drought hardening
treatments consisted in induced water stress by watering restriction,
until pre-dawn stem xylem water potentials (\u3a8pd) reached -0.2,
-1.8 and -2.6 MPa. Two water stress-rewatering cycles were applied
during 54 days of hardening. Plant and root biomasses were affected by
the interaction of drought hardening and genotypes. The rest of
morphological and alometrical traits were affected independently by
drought or genotype. Plant height, leaf area, specific leaf area (SLA),
stem, and leaf biomasses decreased with drought hardening, while collar
diameter was not affected. Genotypes responded differentially to
drought hardening in plant height, leaf area, SLA, and stem, and leaf
biomasses. Ice nucleation temperature (INT), and freezing temperatures
(FRT), and 50% freezing damage index of leaves (LT50) were affected by
the interaction between drought hardening and genotypes. EG-13, EG-23
and EG-22 genotypes became freezing tolerant with drought hardening
(-2.6 MPa). Additionally, EG-14 genotype increased its freezing
resistance at -1.8 MPa. Therefore, freezing resistance levels and
mechanism depend on genotype and drought hardening treatment. The
success in tree breeding by genetic selection should be facilitated by
improved understanding of the physiology of stress resistance
development and survival during water supply limitations. The knowledge
of morphological and freezing resistance dependency on the interaction
between genotype and drought hardening may be useful nursery management
information to improve plantation success
Changes in morpho-physiological attributes of Eucalyptus globulus plants in response to different drought hardening treatments
Morpho-physiological attributes exhibited in response to drought
hardening at the end of the growing season of Eucalyptus globulus
Labill under nursery conditions were studied to evaluate the effect of
three drought hardening treatments in morpho-physiological traits used
as suitable indicators of drought hardiness, such as, plant growth,
root growth potential, plant water relationships and survival. Freezing
resistance of drought hardened plants was also studied in order to
evaluate cross hardening effects in cuttings of Eucalyptus globulus
Labill. Drought hardening consisted in induced water stress by watering
restriction, until plant stem xylem water potentials (\u3a8pd) reached
to-0.2, -1.3 and -2.4 MPa. Two water stress-rewatering cycles were
applied during 54 days of treatment. The hardening treatments caused a
significant reduction in plant height, leaf area, specific leaf area,
plant, leaf, stem and root biomass. However, stem diameter was not
affected. Root growth potential increased with the exposure to moderate
water stress (-1.3 MPa). Drought hardening treatments have not effect
on water relationship parameters such as saturation osmotic potential
(\u3a8\u3c0sat), volumetric module of elasticity (e), relative water
content (RWCtlp) and osmotic potential (\u3a8\u3c0tlp) at the turgor
loss point. Only 1.7% and 6% of dehydrated dead plants were observed on
treatments at -1.3 and -2.4 MPa respectively. Finally, the freezing
damage index of leaves (LT50) was not significantly affected by drought
hardening treatments. Furthermore, a reduction of 1.1\ubaC of
supercooling capacity was observed at -2.4 MPa. As a conclusion,
drought hardening is an important step of plants production programs
during the final phase of nursery, because changes in morphological
attributes caused by exposure to moderate drought, enable the plants to
maintain the balance between transpiration and absorption areas and
increase the capacity of plants to generate new roots
Highlights from the Pierre Auger Observatory
The Pierre Auger Observatory is the world's largest cosmic ray observatory.
Our current exposure reaches nearly 40,000 km str and provides us with an
unprecedented quality data set. The performance and stability of the detectors
and their enhancements are described. Data analyses have led to a number of
major breakthroughs. Among these we discuss the energy spectrum and the
searches for large-scale anisotropies. We present analyses of our X
data and show how it can be interpreted in terms of mass composition. We also
describe some new analyses that extract mass sensitive parameters from the 100%
duty cycle SD data. A coherent interpretation of all these recent results opens
new directions. The consequences regarding the cosmic ray composition and the
properties of UHECR sources are briefly discussed.Comment: 9 pages, 12 figures, talk given at the 33rd International Cosmic Ray
Conference, Rio de Janeiro 201
A search for point sources of EeV photons
Measurements of air showers made using the hybrid technique developed with
the fluorescence and surface detectors of the Pierre Auger Observatory allow a
sensitive search for point sources of EeV photons anywhere in the exposed sky.
A multivariate analysis reduces the background of hadronic cosmic rays. The
search is sensitive to a declination band from -85{\deg} to +20{\deg}, in an
energy range from 10^17.3 eV to 10^18.5 eV. No photon point source has been
detected. An upper limit on the photon flux has been derived for every
direction. The mean value of the energy flux limit that results from this,
assuming a photon spectral index of -2, is 0.06 eV cm^-2 s^-1, and no celestial
direction exceeds 0.25 eV cm^-2 s^-1. These upper limits constrain scenarios in
which EeV cosmic ray protons are emitted by non-transient sources in the
Galaxy.Comment: 28 pages, 10 figures, accepted for publication in The Astrophysical
Journa
Multi-resolution anisotropy studies of ultrahigh-energy cosmic rays detected at the Pierre Auger Observatory
We report a multi-resolution search for anisotropies in the arrival
directions of cosmic rays detected at the Pierre Auger Observatory with local
zenith angles up to and energies in excess of 4 EeV ( eV). This search is conducted by measuring the angular power spectrum
and performing a needlet wavelet analysis in two independent energy ranges.
Both analyses are complementary since the angular power spectrum achieves a
better performance in identifying large-scale patterns while the needlet
wavelet analysis, considering the parameters used in this work, presents a
higher efficiency in detecting smaller-scale anisotropies, potentially
providing directional information on any observed anisotropies. No deviation
from isotropy is observed on any angular scale in the energy range between 4
and 8 EeV. Above 8 EeV, an indication for a dipole moment is captured; while no
other deviation from isotropy is observed for moments beyond the dipole one.
The corresponding -values obtained after accounting for searches blindly
performed at several angular scales, are in the case of
the angular power spectrum, and in the case of the needlet
analysis. While these results are consistent with previous reports making use
of the same data set, they provide extensions of the previous works through the
thorough scans of the angular scales.Comment: Published version. Added journal reference and DOI. Added Report
Numbe
Reconstruction of inclined air showers detected with the Pierre Auger Observatory
We describe the method devised to reconstruct inclined cosmic-ray air showers
with zenith angles greater than detected with the surface array of
the Pierre Auger Observatory. The measured signals at the ground level are
fitted to muon density distributions predicted with atmospheric cascade models
to obtain the relative shower size as an overall normalization parameter. The
method is evaluated using simulated showers to test its performance. The energy
of the cosmic rays is calibrated using a sub-sample of events reconstructed
with both the fluorescence and surface array techniques. The reconstruction
method described here provides the basis of complementary analyses including an
independent measurement of the energy spectrum of ultra-high energy cosmic rays
using very inclined events collected by the Pierre Auger Observatory.Comment: 27 pages, 19 figures, accepted for publication in Journal of
Cosmology and Astroparticle Physics (JCAP
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