Recent climatic changes significantly affected forest ecosystems in northern Eurasia. Trees growing in Siberia are very sensitive to climate change due to strong temperature limitation of their growth. Our study covers high-latitude (northeastern Yakutia, eastern Taimyr, central Evenkia) and high-altitude (Russian Altai) zones in Eurasia, where tree-ring parameters (tree-ring width, cell-wall thickness, and maximum latewood density) mainly record summer air temperature variations. To reveal the impact of moisture changes (e.g., amount of precipitation, vapor pressure deficit, relative humidity and potential evapotranspiration) on tree growth in Siberian forest ecosystems, we evaluated delta C-13 in tree-ring cellulose over the past century. We found that at all the study sites mainly June-July precipitation and June-July evapotranspiration affect larch radial growth, while the strongest influence of vapor pressure deficit on the delta C-13 was observed in northeastern Yakutia. Further increase of vapor pressure deficit and rise of air temperature in the coming decades in Siberian regions will probably lead to drought and related forest mortality even under additional source of water due to permafrost thaw.

Climate change is expected to alter the mechanisms controlling soil organic matter (SOM) stabilization. Under climate change, soil warming and drying could affect the enzymatic mechanisms that control SOM turnover and dependence on substrate concentration. Here, we used a greenhouse climate manipulation in a mature boreal forest soil to test two specific hypotheses: (1) Rates of decomposition decline at lower substrate concentrations, and (2) reductions in soil moisture disproportionately constrain the degradation of low-concentration substrates. Using constructed soil cores, we measured decomposition rates of two polymeric substrates, starch and cellulose, as well as enzyme activities associated with degradation of these substrates. The greenhouse manipulation increased temperature by 0.8 A degrees C and reduced moisture in the constructed cores by up to 90 %. We rejected our first hypothesis, as the rate of starch decomposition did not decrease with declining starch concentration under control conditions, but we did find support for hypothesis two: Drying led to lower decomposition rates for low-concentration starch. We observed a threefold reduction in soil respiration rates in bulk soils in the greenhouses over a 4-month period, but the C losses from the constructed cores did not vary among our treatments. Activities of enzymes that degrade cellulose and starch were elevated in the greenhouse treatments, which may have compensated for moisture constraints on the degradation of the common substrate (i.e., cellulose) in our constructed cores. This study confirms that substrate decomposition can be concentration-dependent and suggests that climate change effects on soil moisture could reduce rates of decomposition in well-drained boreal forest soils lacking permafrost.