Soil Organic Matter Dynamics in Boreal Ecosystems in Eurasia

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The main results obtained in the present study, in which soil organic matter (SOM) dynamics in boreal ecosystems in Eurasia were investigated, are listed below:1) Transition of soils and vegetation influenced by climatic conditions that change along with elevation or latitude were surveyed in different regions of Eurasia and North America; that is, southeastern Kazakhstan, Finland, West Siberia and Canada. Generally a clear zonation was observed within respective study regions, indicating that the SOM dynamics would be formulated primarily by location data.2) A field experiment was conducted using the stable isotope tracer method at the five different soils in northern Tienshan to clarify the decomposition rate of ^<13>C labeled plant materials and the splitting ratio of C derived from the plant materials that migrates to HF on whole substrates utilized. Both the decomposition rate constant and splitting ratio of decomposed plant materials that migrate to either HF or CO_2 varied consi … More derably among the different slope directions.3) Utilization of SOM by soil microbes in the soils from northern Tienshan was investigated in detail by analyzing patterns of glucose utilization after addition of low levels of glucose C. The experimental results indicated that there was a threshold concentration of glucose over which structural compounds started to be synthesized from storage compounds in soil microbes and the ratio of respiration to assimilation started to increase, and that a higher proportion of substrates may be easily mineralized in acid and/or disturbed soils in situations where higher concentrations of substrates are occasionally supplied with temporal 'C flushes' such as may occur in the rhizosphere or in the vicinity of plant residues.4) To optimize regional crop rotation systems for mitigating SOM depletion, spatial and temporal variation of the SOM budget was monitored could be feasible options and that the methodology of geostatistics was useful to simulate SOM dynamics in a regional scale considering spatial heterogeneity of soil resources according to topography. Less