•Larch stand transpired 24% more water than Scots pine stand.•Stomatal conductance was more strictly regulated in pine than in larch when evapotranspiration demands were high.•Larch transpiration at ...high VPD progressively declined from the beginning to the end of the summer.
Russian boreal forests represent the largest forested region on Earth and comprise one-fifth of the world's forest cover. The two most common genera in Siberia are Larix and Pinus, which together cover more than 80% of the region’s forested area. One observable ongoing effect of climate warming is that natural populations of Siberian larch are gradually being replaced by Scots pine. The present work focuses on comparing effects of environmental variables on sap flow density in two even-aged stands of Larix sibirica and Pinus sylvestris. While the two study stands were identical in age (49 years) with similar basal areas and leaf area index, they exhibited very different transpiration rates and response mechanisms to environmental signals. Stand water use was higher for larch than it was for pine, even though transpiration for deciduous larch trees occurred over shorter time periods. The cumulative annual transpiration of the larch stand was 284 ± 4 mm measured over two consecutive growing seasons (2015–2016), while for pine this was 20% lower. Seasonal transpiration accounted for 50% and 40% of the reference evapotranspiration and 91% and 67% of growing season precipitation for larch and pine, respectively. Water stored in soil provided an important source of water for transpiration, observed as roughly 100 mm, which was then replenished from snowmelt the following spring. The greatest difference between two species related to how well they controlled transpiration, notably in the context of high vapor pressure deficit; under these conditions, pine maintained greater control over transpiration than larch. For all soil moisture levels measured, larch transpired more water than pine. Importantly, our results point to potential future effects of global warming, most notably an increasing decline of larch forests, changes in the ratio between latent and sensitive heat fluxes, and significant modifications in ecosystem water availability.
Stratospheric volcanic eruptions have far-reaching impacts on global climate and society. Tree rings can provide valuable climatic information on these impacts across different spatial and temporal ...scales. To detect temperature and hydroclimatic changes after strong stratospheric Common Era (CE) volcanic eruptions for the last 1500 years (535 CE unknown, 540 CE unknown, 1257 CE Samalas, 1640 CE Parker, 1815 CE Tambora, and 1991 CE Pinatubo), we measured and analyzed tree-ring width (TRW), maximum latewood density (MXD), cell wall thickness (CWT), and delta.sup.13 C and delta.sup.18 O in tree-ring cellulose chronologies of climate-sensitive larch trees from three different Siberian regions (northeastern Yakutia - YAK, eastern Taimyr - TAY, and Russian Altai - ALT).
Abstract
The effective mass at the Fermi level is measured in the strongly interacting two-dimensional (2D) electron system in ultra-clean SiGe/Si/SiGe quantum wells in the low-temperature limit in ...tilted magnetic fields. At low electron densities, the effective mass is found to be strongly enhanced and independent of the degree of spin polarization, which indicates that the mass enhancement is not related to the electrons’ spins. The observed effect turns out to be universal for silicon-based 2D electron systems, regardless of random potential, and cannot be explained by existing theories.
Ignited by the discovery of the metal-insulator transition, the behaviour of low-disorder two-dimensional (2D) electron systems is currently the focus of a great deal of attention. In the strongly ...interacting limit, electrons are expected to crystallize into a quantum Wigner crystal, but no definitive evidence for this effect has been obtained despite much experimental effort over the years. Here, studying the insulating state of a 2D electron system in silicon, we have found two-threshold voltage-current characteristics with a dramatic increase in noise between the two threshold voltages. This behaviour cannot be described within existing traditional models. On the other hand, it is strikingly similar to that observed for the collective depinning of the vortex lattice in type-II superconductors. Adapting the model used for vortexes to the case of an electron solid yields good agreement with our experimental results, favouring the quantum electron solid as the origin of the low-density state.
Climate change projections forecast most significant impacts on high-latitude forest ecosystems. Particularly, climate warming in boreal regions should increase fire severity and shorten its return ...interval. These processes can change the dynamics of boreal forests as younger stands become more dominating with a shift from gymnosperm to angiosperm. However, despite angiosperm's phenological and physiological traits have a high potential for ecophysiological and dendroclimatological studies in Siberia, they have been rarely investigated due to their short-term lifespan in comparison with gymnosperm. Modeling tree growth is a common way to understand tree growth responses to environmental changes since it allows using available experiment or field data to interpret observed climate-growth relationships based on the biological principles. In our study, we applied the process-based Vaganov-Shashkin (VS) model of tree-ring growth
a parameterization approach VS-oscilloscope for the first time to an angiosperm tree species (
Ehrh.) from continuous permafrost terrain to understand its tree-radial growth dynamic. The parameterization of the VS model provided highly significant positive correlations (
< 0.05) between the simulated growth curve and initial tree-ring chronologies for the period 1971-2011 and displayed the average duration of the growing season and intra-seasonal key limiting factors for xylem formation. Modeled result can be valid at the regional scale for remote birch stands, whereas, justification of the local non-climatic input data of the model provided precise site-specific tree growth dynamic and their substantiated responses to driving factors.
We review the latest developments in the field of the metal-insulator transition in strongly-correlated two-dimensional electron systems. Particular attention is given to recent discoveries of a ...sliding quantum electron solid and interaction-induced spectrum flattening at the Fermi level in high-quality silicon-based structures.
The increase in the resistivity with decreasing temperature followed by a drop by more than one order of magnitude is observed on the metallic side near the zero-magnetic-field metal-insulator ...transition in a strongly interacting two-dimensional electron system in ultra-clean SiGe/Si/SiGe quantum wells. We find that the temperature Formula: see text, at which the resistivity exhibits a maximum, is close to the renormalized Fermi temperature. However, rather than increasing along with the Fermi temperature, the value Formula: see text decreases appreciably for spinless electrons in spin-polarizing (parallel) magnetic fields. The observed behaviour of Formula: see text cannot be described by existing theories. The results indicate the spin-related origin of the effect.
We show that the merging of the spin- and valley-split Landau levels at the chemical potential is an intrinsic property of a strongly interacting two-dimensional electron system in silicon. Evidence ...for the level merging is given by available experimental data.
The first results on the development of an original power GaAs-based field-effect transistor with a vertical channel controlled by a
p
–
n
junction are presented. The main manufacturing feature is ...the use of two separate epitaxial growth processes when forming the transistor structure. The transistor part containing the drain, drift, and gate regions is grown by liquid-phase epitaxy. Metalorganic gas-phase epitaxy is used to form the channel and source regions.
•Eu2+-doped BaAl2Si2O8 glass-ceramics have been prepared by glass melting.•Different nanocrystals are formed during BaO-Al2O3-SiO2−MgF2 glass crystallization.•Eu3+ ions are reduced during ...crystallization and luminescence of Eu2+ ions growths.
Transparent Eu2+-doped BaAl2Si2O8 glass-ceramics have been prepared by traditional glass melting method. The evolution of synthesized materials during thermal treatment in air atmosphere was studied by X-ray diffraction analysis and photoluminescence spectroscopy. Thermal treatment of glass in air atmosphere leads to the formation of numerous crystal phases, the main of them is BaAl2Si2O8. Obtained glass-ceramics demonstrate strong blue emission (λmax = 420 nm) related to the 5d-4f7 transition of Eu2+ ions. Prepared transparent Eu2+-doped BaAl2Si2O8 glass ceramics can be considered as potential candidate for practical application in powerful white light-emitting diodes.
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