Seasonal Dynamic of soil organic matter in Forest Soil.

Soil organic matter (SOM) is one of the most important components of a field ecosystem. Changes in SOM may be difficult to monitor in the short term because of (1) low magnitude of change, (2) high background carbon levels and (3) high natural variability of soils. The microbial biomass carbon (MBC) has been suggested as a useful and sensitive measure of a change in SOM status and composition, providing a useful indicator of soil processes. The objectives of the present study were to 1) evaluate the seasonal fluctuation of SOM and MBC in a forest soil and 2) determine the relationship between SOM and MBC. The results indicate a seasonal variation of soil organic matter and microbial biomass, with the greatest amount of microbial biomass in summer and the lowest content in winter. In addition, variation in SOM composition was also observed with the largest concentrations of water-soluble phenolic acids in autumn and the smallest in summer; the greatest amount of humic matter was in winter and the smallest one in summer. HC/FC ratio also changed, with the highest value in winter and autumn and the lowest one in summer. These results show that seasonal fluctuations are well reflected in microclimate in terms of soil moisture and temperature that rapidly affect the amount and the activity of SMB. These in turn influence the dynamic and the composition of SOM. The results obtained suggest that carbon cycling responses to environmental change can be highly ecosystem–specific and thus needs to be verified across different ecosystems.