Stable oxygen isotope ratios of plant water (sap water) were observed at Spasskaya Pad experimental forest near Yakutsk, Russia in 1997–1999. The δ18O of sap water in larch trees (Larix gmelinii) decreased soon after leaf unfolding every year, indicating that snowmelt water was used in the beginning of summer. During mid to late summer, a clear difference in the water source used by plants was observed between wet summers and severe drought summers. The δ18O values of water in larch trees were high (−17.8 to −16.1‰) in August 1999 (wet summer), but low (−20.4 to −19.7‰) in August 1998 (drought summer). These results indicated that plants used rainwater during a wet summer, but meltwater from permafrost was used by plants during a drought summer. One important role of permafrost is to provide a direct source of water for plants in a severe drought summer; another role is to keep surplus water in the soil until the next summer. If this permafrost system is disturbed by future global warming, unique monotypic stands of deciduous larch trees in east Siberia might be seriously damaged in a severe drought summer.

Abstract:Soil moisture and its isotopic composition were observed at Spasskaya Pad experimental forest near Yakutsk, Russia, during summer in 1998Russia, during summer in , 1999Russia, during summer in , and 2000. The amount of soil water (plus ice) was estimated from volumetric soil water content obtained with time domain reflectometry. Soil moisture and its υ 18 O showed large interannual variation depending on the amount of summer rainfall. The soil water υ 18 O decreased with soil moisture during a dry summer (1998), indicating that ice meltwater from a deeper soil layer was transported upward. On the other hand, during a wet summer (1999), the υ 18 O of soil water increased due to percolation of summer rain with high υ 18 O values. Infiltration after spring snowmelt can be traced down to 15 cm by the increase in the amount of soil water and decrease in the υ 18 O because of the low υ 18 O of deposited snow. About half of the snow water equivalent (about 50 mm) recharged the surface soil. The pulse of the snow meltwater was, however, less important than the amount of summer rainfall for intra-annual variation of soil moisture.Excess water at the time just before soil freezing, which is controlled by the amount of summer rainfall, was stored as ice during winter. This water storage stabilizes the rate of evapotranspiration. Soil water stored in the upper part of the active layer (surface to about 120 cm) can be a water source for transpiration in the following summer. On the other hand, once water was stored in the lower part of the active layer (deeper than about 120 cm), it would not be used by plants in the following summer, because the lower part of the active layer thaws in late summer after the plant growing season is over.

[1] We studied the relationships between earlywood/latewood width, stable carbon isotope ratio (d 13 C) of cellulose, and soil moisture at a dry and a wet site in Yakutsk, eastern Siberia, which differed considerably in soil water conditions. Recharge of soil water by snowmelt in spring and subsequent drought in summer provided a marked seasonal contrast in soil water conditions between the earlywood and latewood formation period. Ring index was calculated by dividing each earlywood/latewood width by the 5-year averaged width for each individual. In order to determine whether drought influenced the ring index-d 13 C relation, the ring index time series were compared with d 13 C time series. We collected wood samples from eight Larix gmelinii (Rupr.) Rupr. and four Pinus sylvestris L. trees from the two sites and measured the earlywood and latewood widths and d 13 C of earlywood and latewood formed during the years 1996-2000. At the dry site, seasonal soil water content variation corresponded to seasonal d 13 C variation of tree rings. We found negative ring index-d 13 C correlations in latewood for both species at the dry site mainly dominated by Pinus but not in latewood of Larix at the wet site dominated by Larix. Decrease and/or early cessation of latewood growth and increase in d 13 C under drought conditions possibly explain this negative correlation. This suggests the growth limitation of trees in this region by drought and the prospects of reconstructing past drought with latewood d 13 C of the dry site.

Terminal tetraloops consisting of GNRA sequences are often found in biologically active large RNAs. The loops appear to contribute towards the organization of higher order RNA structures by forming specific tertiary interactions with their receptors. Group IC3 introns which possess a GAAA loop in the L2 region often have a phylogenetically conserved motif in their P8 domains. In this report, we show that this conserved motif stands as a new class of receptor that distinguishes the sequences of GNRA loops less stringently than previously known receptors. The motif can functionally substitute an 11 nt motif receptor in the Tetrahymena ribozyme. Its structural and functional similarity to one class of synthetic receptors obtained from in vitro selection is observed.

Weather conditions for concurrent widespread fires in boreal forests were examined by various weather maps and temperature charts. The four study regions in boreal forests are three in East Siberia and one in Alaska. We applied preliminary analysis method for Sakha proposed by the authors to show the effectiveness of our approach. More than 12 very active fire-periods were identified from satellite hotspot data. Analysis results clearly showed fires during all active fire-periods became very active as warm air masses from south approached four study regions. These movements of warm air masses were mainly related to the meandering of large westerlies. To explain the large increase of daily hotspots (fires) during active fire-periods, a preliminary wind analysis was carried out. Strong wind conditions occurred when warm and dry air masses were approaching, stagnating, and passing over Southern Sakha under various weather conditions at lower air. During the top fire-period in Southern Sakha, wind velocity at lower air (925 hPa) changed from about 1 to 8 m/s while number of hotspot increased from around 1000 to 9000.