[1] 'Alases' are mature thermokarst depressions covered by grassland distributed in taiga forests in central Yakutia, eastern Siberia, following thermokarst formation initiated in early Holocene. Alases are important land-cover class in the central Yakutia lowland occupying 17% of the total land area. CH 4 and N 2 O fluxes were measured temporally in a typical alas which have a pond at the center during the growing season of two years. Seven monitoring plots represented various vegetation types: a larch forest (F), a dry grassland (DG), four wet grasslands (WG) flooded temporarily or continuously, and a pond surface (P) flooded continuously without vegetation. The pond flooding area reached its maximum just after snow-melting and decreased during the summer. The F and DG plots were small CH 4 sinks. The wet plots (including WG and P) were large CH 4 sources (cumulative value of growing season: 17 to 864 kg CH 4 -C ha À1 ), and emission rates vary drastically depending on flooding conditions. All plots were slight sources or sinks of N 2 O except for the WG plots (0.16 to 1.7 kg N 2 O-N ha À1 ) where peak emissions were observed after the flooding ended. The global warming potentials (time horizon of 100 years) of the cumulative N 2 O emissions from the plots were lower than those of each CH 4 emissions. Estimated total CH 4 emission from the whole WG area (7.93 ha) accounted for 88% of the emission from the whole alas (28.9 ha). The current permafrosttaiga region in central Yakutia could be a net CH 4 source owing to the presence of alases.

Salinity is at present one of the most serious environmental problems in¯uencing crop growth. It has been extensively demonstrated that salinity aects several physiological processes in the plant, including the plant±water relations of most salt-sensitive crops species. In this study, the eects of salinity on the plant±water relations of kidney bean (Phaseolus vulgaris L.) and the possibility that foliarly applied glycinebetaine improves these water relations are examined. Kidney bean plants were grown in a greenhouse and treated with 0, 30, 50 and 100 mM M NaCl, combined with 0, 10 and 30 mM M glycinebetaine in foliar applications. Increased salinity levels decreased stomatal conductance, photosynthetic rate, transpiration and leaf relative water content in the 30, 50 and 100 mM M treatments relative to the control treatment. Glycinebetaine applications of 10 mM M increased stomatal conductance at 50 mM M NaCl, ameliorating signi®cantly the eect of salinity on water relations through increases in the leaf relative water content. At 100 mM M NaCl, 30 mM M glycinebetaine applications in particular contributed to osmotic stress, and had an adverse eect on plants. Our experiment suggests that glycinebetaine can be used as an alternative treatment to reduce the eects of salt stress on the water relations of salt-sensitive plants, but only to limited salinity levels. Furthermore, the improvement in the water status of kidney beans was dose dependent, suggesting that the concentration of glycinebetaine essential for the survival of salt-sensitive plants is species speci®c and must be determined individually for each plant species.

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To evaluate the effect of increasing forest disturbances on greenhouse gas budgets in a taiga forest in eastern Siberia, CO 2 , CH 4 and N 2 O fluxes from the soils were measured during the growing season in intact, burnt and clear-felled larch forests (4-5 years after the disturbance). Soil temperature and moisture were higher at the two disturbed sites than at the forest site. A 64-72% decrease in the Q 10 value of soil CO 2 flux from the disturbed sites compared with the forest site (5.92) suggested a reduction in root respiration and a dominance of organic matter decomposition at the disturbed sites. However, the cumulative CO 2 emissions (May-August) were not significantly different among the sites (2.81-2.90 Mg C ha -1 per 3 months). This might be because decreased larch root respiration was compensated for by increased organic matter decomposition resulting from an increase in the temperature and root respiration of invading vegetation at the disturbed sites. The CH 4 uptake (kg C ha -1 per 4 months [May-September]) at the burnt site was significantly higher (-0.15) than the uptake at the forest (-0.045) and clear-felled sites (0.0027). Although there were no significant differences among the sites, N 2 O emission (kg N ha -1 per 4 months) was slightly lower at the burnt site (0.013) and higher at the clear-felled site (0.068) than at the forest site (0.038). This different influence of burning and tree felling on CH 4 and N 2 O fluxes might result from changes in the physical and chemical properties of the soil with respect to forest fire.Greenhouse gas flux in disturbed taiga forest soil 939