558 research outputs found
Diurnal cycles of embolism formation and repair in petioles of grapevine (Vitis vinifera cv. Chasselas)
The impact of water deficit on stomatal conductance (gs), petiole hydraulic conductance (Kpetiole), and vulnerability to cavitation (PLC, percentage loss of hydraulic conductivity) in leaf petioles has been observed on field-grown vines (Vitis vinifera L. cv. Chasselas). Petioles were highly vulnerable to cavitation, with a 50% loss of hydraulic conductivity at a stem xylem water potential (Ψx) of –0.95 MPa, and up to 90% loss of conductivity at a Ψx of –1.5 MPa. Kpetiole described a daily cycle, decreasing during the day as water stress and evapotranspiration increased, then rising again in the early evening up to the previous morning's Kpetiole levels. In water-stressed vines, PLC increased sharply during the daytime and reached maximum values (70–90%) in the middle of the afternoon. Embolism repair occurred in petioles from the end of the day through the night. Indeed, PLC decreased in darkness in water-stressed vines. PLC variation in irrigated plants showed the same tendency, but with a smaller amplitude. The Chasselas cultivar appears to develop hydraulic segmentation, in which petiole cavitation plays an important role as a ‘hydraulic fuse’, thereby limiting leaf transpiration and the propagation of embolism and preserving the integrity of other organs (shoots and roots) during water stress. In the present study, progressive stomatal closure responded to a decrease in Kpetiole and an increase in cavitation events. Almost total closure of stomata (90%) was measured when PLC in petioles reached >90%
Plant/Leaf traits and adaptive strategies of Cistus species to Mediterranean drought and insolation in southern Portugal
The effects of climate change can result in dramatic consequences in specific ecosystems such as montados that are seriously threatened by the absence of cork and holm oak (Quercus suber and Q. rotundifolia) natural regeneration. Shrubs of the genus Cistus, which are among the most important elements of encroached montados, seem to promote soil rehabilitation and enhance oak regeneration (Simões et al. 2009). In this context, we compared the life strategies and evaluated the potential ability of Cistus species to adapt to the increasing drought expected for the Mediterranean region, and thus their role on the sustainability of cork oak montados
Cork oak (Quercus suber L.) seedlings acclimate to elevated
Leaf gas-exchange, leaf and shoot anatomy,
wood density and hydraulic conductivity were investigated in
seedlings of Quercus suber L. grown for 15 months either at
elevated (700 lmol mol-1) or normal (350 lmol mol-1)
ambient atmospheric CO2 concentrations. Plants were
grown in greenhouses in a controlled environment: relative
humidity 50% (±5), temperature similar to external temperature
and natural light conditions. Plants were supplied
with nutrients and two water regimes (WW, well watered;
WS, water stress). After 6 months exposure to CO2
enrichment an increase in photosynthetic rate, a decrease in
stomatal conductance and a decrease in carbon isotope
discrimination (D13C) were observed, along with enhanced
growth and an increase in the number of branches and
branch diameter. Over the same period, the shoot weight
ratio increased, the root weight ratio decreased and the leaf
weight ratio was unaffected. The specific leaf area increased
due to an increase in total leaf thickness, mainly due to the
palisade parenchyma and starch. However, after 9 and
15 months of elevated CO2 exposure, the above-mentioned
physiological and morphological parameters appeared to be
unaffected. Elevated CO2 did not promote changes in vessel
lumen diameter, vessel frequency or wood density in stems
grown in greenhouse conditions. As a consequence, xylem
hydraulic efficiency remained unchanged. Likewise, xylem
vulnerability to embolism was not modified by elevated
CO2. In summary, elevated CO2 had no positive effect on
the ecophysiological parameters or growth of water stressed
plants
Horizontal rotation signals detected by "G-Pisa" ring laser for the Mw=9.0, March 2011, Japan earthquake
We report the observation of the ground rotation induced by the Mw=9.0, 11th
of March 2011, Japan earthquake. The rotation measurements have been conducted
with a ring laser gyroscope operating in a vertical plane, thus detecting
rotations around the horizontal axis. Comparison of ground rotations with
vertical accelerations from a co-located force-balance accelerometer shows
excellent ring laser coupling at periods longer than 100s. Under the plane wave
assumption, we derive a theoretical relationship between horizontal rotation
and vertical acceleration for Rayleigh waves. Due to the oblique mounting of
the gyroscope with respect to the wave direction-of-arrival, apparent
velocities derived from the acceleration / rotation rate ratio are expected to
be always larger than, or equal to the true wave propagation velocity. This
hypothesis is confirmed through comparison with fundamental-mode, Rayleigh wave
phase velocities predicted for a standard Earth model.Comment: Accepted for publication in Journal of Seismolog
Herbaceous angiosperms are not more vulnerable to drought-induced embolism than angiosperm trees
The water transport pipeline in herbs is assumed to be more vulnerable to drought than in trees due to the formation of frequent
embolisms (gas bubbles), which could be removed by the occurrence of root pressure, especially in grasses. Here, we studied
hydraulic failure in herbaceous angiosperms by measuring the pressure inducing 50% loss of hydraulic conductance (P50) in stems
of 26 species, mainly European grasses (Poaceae). Our measurements show a large range in P50 from 20.5 to 27.5 MPa, which
overlaps with 94% of the woody angiosperm species in a worldwide, published data set and which strongly correlates with an
aridity index. Moreover, the P50 values obtained were substantially more negative than the midday water potentials for five grass
species monitored throughout the entire growing season, suggesting that embolism formation and repair are not routine and
mainly occur under water deficits. These results show that both herbs and trees share the ability to withstand very negative water
potentials without considerable embolism formation in their xylem conduits during drought stress. In addition, structure-function
trade-offs in grass stems reveal that more resistant species are more lignified, which was confirmed for herbaceous and closely
related woody species of the daisy group (Asteraceae). Our findings could imply that herbs with more lignified stems will
become more abundant in future grasslands under more frequent and severe droughts, potentially resulting in lower forage
digestibility.
The magnetic field of the B3V star 16 Pegasi
The Slowly Pulsating B3V star 16 Pegasi was discovered by Hubrig (2006) to be
magnetic, based on low-resolution spectropolarimetric observations with FORS1
at the VLT. We have confirmed the presence of a magnetic field with new
measurements with the spectropolarimeters Narval at TBL, France and Espadons at
CFHT, Hawaii during 2007. The most likely period is about 1.44 d for the
modulation of the field, but this could not be firmly established with the
available data set. No variability has been found in the UV stellar wind lines.
Although the star was reported once to show H alpha in emission, there exists
at present no confirmation that the star is a Be star.Comment: 2 pages, 4 figures, contrubuted poster at IAU Symposium 259 "Cosmic
Magnetic Fields: from Planets, to Stars and Galaxies", Tenerife, Spain,
November 3-7, 200
SurEau-Ecos v2.0: a trait-based plant hydraulics model for simulations of plant water status and drought-induced mortality at the ecosystem level
A widespread increase in tree mortality has been observed
around the globe, and this trend is likely to continue because of ongoing
climate-induced increases in drought frequency and intensity. This raises
the need to identify regions and ecosystems that are likely to experience
the most frequent and significant damage. We present SurEau-Ecos, a trait-based,
plant hydraulic model designed to predict tree desiccation and mortality at
scales from stand to region. SurEau-Ecos draws on the general principles of the SurEau model
but introduces a simplified representation of plant architecture and
alternative numerical schemes. Both additions were made to facilitate model
parameterization and large-scale applications. In SurEau-Ecos, the water fluxes from
the soil to the atmosphere are represented through two plant organs (a leaf
and a stem, which includes the volume of the trunk, roots and branches) as
the product of an interface conductance and the difference between water
potentials. Each organ is described by its symplasmic and apoplasmic
compartments. The dynamics of a plant's water status beyond the point of
stomatal closure are explicitly represented via residual transpiration flow,
plant cavitation and solicitation of plants' water reservoirs. In addition
to the “explicit” numerical scheme of SurEau, we implemented a “semi-implicit”
and “implicit” scheme. Both schemes led to a substantial gain in computing
time compared to the explicit scheme (>10 000 times), and
the implicit scheme was the most accurate. We also observed similar plant
water dynamics between SurEau-Ecos and SurEau but slight disparities in infra-daily
variations of plant water potentials, which we attributed to the differences
in the representation of plant architecture between models. A global model's
sensitivity analysis revealed that factors controlling plant desiccation
rates differ depending on whether leaf water potential is below or above the
point of stomatal closure. Total available water for the plant, leaf area
index and the leaf water potential at 50 % stomatal closure mostly drove
the time needed to reach stomatal closure. Once stomata are closed,
resistance to cavitation, residual cuticular transpiration and plant water
stocks mostly determined the time to hydraulic failure. Finally, we
illustrated the potential of SurEau-Ecos to simulate regional drought-induced mortality
over France. SurEau-Ecos is a promising tool to perform regional-scale predictions of
drought-induced hydraulic failure, determine the most vulnerable areas and
ecosystems to drying conditions, and assess the dynamics of forest
flammability.</p
Desiccation and mortality dynamics in seedlings of different European beech (Fagus sylvatica L.) populations under extreme drought conditions
European beech (Fagus sylvatica L., hereafter beech), one of the major native tree species in Europe, is known to be drought sensitive. Thus, the identification of critical thresholds of drought impact intensity and duration are of high interest for assessing the adaptive potential of European beech to climate change in its native range. In a common garden experiment with one-year-old seedlings originating from central and marginal origins in six European countries (Denmark, Germany, France, Romania, Bosnia-Herzegovina, and Spain), we applied extreme drought stress and observed desiccation and mortality processes among the different populations and related them to plant water status (predawn water potential, 9PD) and soil hydraulic traits. For the lethal drought assessment, we used a critical threshold of soil water availability that is reached when 50% mortality in seedling populations occurs (LD50SWA). We found significant population differences in LD50SWA (10.5-17.8%), and mortality dynamics that suggest a genetic difference in drought resistance between populations. The LD50SWA values correlate significantly with the mean growing season precipitation at population origins, but not with the geographic margins of beech range. Thus, beech range marginality may be more due to climatic conditions than to geographic range. The outcome of this study suggests the genetic variation has a major influence on the varying adaptive potential of the investigated populations
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