Factors Controlling in situ Decomposition Rate of Soil Organic Matter under Various Bioclimatic Conditions of Eurasia(<Special Issue>International Symposium: Challenges to Soil Degradation Towards Sustaining Life and Environment, Tokyo Metropolitan University Symposium Series No.2, 2009)

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  • Factors controlling in situ decomposition rate of soil organic matter under various bioclimatic conditions of Eurasia

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Field measurements of soil respiration were carried out under various bioclimatic conditions in Eurasia. The data were simultaneously analyzed to identify factors that control the in situ soil respiration and its temperature and moisture dependence, together with the laboratory incubation data to support the analysis of field data. We obtained the following results: 1) In the stepwise regression analysis for estimating the in situ total soil respiration and microbial soil respiration using soil temperature and moisture as explanatory variables, activation energy (E), which is a temperature-dependent factor, was preferentially selected in the temperate plots, whereas the coefficient for moisture dependence (b) was primarily selected for the tropical plots. 2) Both the incubation and field experiments suggested that E was higher in the tropical zone than in the temperate zones; however, there was some uncertainty in the microbial soil respiration determined in the field. Therefore, we speculate that the direct influence of climatic change (i.e., global warming) on the acceleration of soil organic matter (SOM) decomposition and the accompanying decrease in its stock would be more conspicuous in the tropics than in other zones. 3) The moisture coefficient b and decomposition rate constant k are often higher in cropland than forest or grassland. The conversion of land-use from natural vegetation to cropland can, therefore, accelerate SOM decomposition, owing to the increase in the decomposition rate constant in addition to the decrease in litter incorporation into the soil after reclamation. 4) A close relationship was found between annual microbial respiration (AMR) and annual total soil respiration (ATR): AMR=0.550(ATR)-0.015; (R^2=0.81^<**>, n=19). That is, approximately 55% of the total soil respiration originates from the activity of soil microbes and the remaining 45% from plant roots. 5) Positive correlation was found between the decomposition rate constant k determined from the incubation experiment and that based on field measurements. The laboratory incubation experiment, therefore, was demonstrated to be useful for simulating the in situ dynamics of SOM and analyzing the temperature and moisture dependence of the SOM dynamics.

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