Plant-Soil-Climate Interaction in Observed and Simulated Tree-Radial Growth Dynamics of Downy Birch in Permafrost.

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 via a parameterization approach VS-oscilloscope for the first time to an angiosperm tree species (Betula pubescens Ehrh.) from continuous permafrost terrain to understand its tree-radial growth dynamic. The parameterization of the VS model provided highly significant positive correlations (p < 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.

Do centennial tree-ring and stable isotope trends of Larix gmelinii (Rupr.) Rupr. indicate increasing water shortage in the Siberian north?

Tree-ring width of Larix gmelinii (Rupr.) Rupr., ratios of stable isotopes of C (delta(13)C) and O (delta(18)O) of whole wood and cellulose chronologies were obtained for the northern part of central Siberia (Tura, Russia) for the period 1864-2006. A strong decrease in the isotope ratios of O and C (after atmospheric delta(13)C corrections) and tree-ring width was observed for the period 1967-2005, while weather station data show a decrease in July precipitation, along with increasing July air temperature and vapor pressure deficit (VPD). Temperature at the end of May and the whole month of June mainly determines tree radial growth and marks the beginning of the vegetation period in this region. A positive correlation between tree-ring width and July precipitation was found for the calibration period 1929-2005. Positive significant correlations between C isotope chronologies and temperatures of June and July were found for whole wood and cellulose and negative relationships with July precipitation. These relationships are strengthened when the likely physiological response of trees to increased CO(2) is taken into account (by applying a recently developed delta(13)C correction). For the O isotope ratios, positive relationships with annual temperature, VPD of July and a negative correlation with annual precipitation were observed. The delta(18)O in tree rings may reflect annual rather than summer temperatures, due to the late melting of the winter snow and its contribution to the tree water supply in summer. We observed a clear change in the isotope and climate trends after the 1960s, resulting in a drastic change in the relationship between C and O isotope ratios from a negative to a positive correlation. According to isotope fractionation models, this indicates reduced stomatal conductance at a relatively constant photosynthetic rate, as a response of trees to water deficit for the last half century in this permafrost region.

Influence of reducing-oxidizing conditions on the optical properties of Co(2+)-doped magnesium aluminosilicate glass ceramics and their use as an effective saturable absorber Q switch.

Nonlinear optical properties of Co(2+)-doped magnesium aluminosilicate glass ceramics prepared under normal and reducing conditions are studied in the range of the 4A2 --> 4T1(4F) transition of tetrahedral Co2+ ions. The results of passive Q switching of a 1.54-microm Er3+:glass laser with saturable absorbers made of Co(2+)-doped glass ceramics prepared at different conditions are presented. Q-switched pulses of 60 ns in duration and of 4.6 mJ in energy, corresponding to approximately 20% of the Q-switching conversion efficiency, are achieved.

Magnesium- and zinc-aluminosilicate cobalt-doped glass ceramics as saturable absorbers for diode-pumped 1.3-microm laser.

Q switching of a diode-pumped Nd3+:KGd(WO4)2 laser at 1.35 microm by use of cobalt-doped magnesium- and zinc-aluminosilicate glass ceramics as saturable absorbers is demonstrated. Q-switching efficiency up to 40% has been obtained. Ground-state absorption cross sections for Co2+ ions at the wavelengths of 1.35 and 1.54 microm are estimated to be (3.5-4.0) x 10(-19) cm2. Bleaching relaxation times under the excitation of the 4A2 --> 4T1(4F) transition of tetrahedrally coordinated Co2+ ions are of 280 +/- 50 ns and 700 +/- 80 ns for magnesium- and zinc-aluminosilicate glass ceramics, respectively.