Effect of Soil Moisture on Soil Microbial Biomass in Loblolly Pine (Pinus taeda) Stand.

In the forest ecosystem, soil microbial biomass (SMB) plays a significant role in plant residue decomposition and subsequent release of plant nutrients to the soil. SMB is measured by the amount of carbon (C) and nitrogen (N) present in the microorganisms and is affected by various factors, such as the amount of moisture present in the soil. In 2016, a study was carried out for four consecutive seasons to determine the effect of soil moisture content (SMC) in SMB and the seasonal variation in the study site located in Eufaula, Alabama, United States. Soil samples were collected in the winter, spring, summer and the fall from fifteen different plots starting from January 2016. After sieving the soil samples with 2mm mesh size sieve, soil microbial biomass carbon (SMB-C) and soil microbial biomass nitrogen (SMB-N) at the depth of 0-10 cm were determined by soil fumigation with alcohol-free chloroform (CHCl₃) and extraction with 0.5 M K₂SO₄. The maximum SMB-C of 156.427 mg/L and the minimum of 18.689 mg/L were recorded in the spring and the fall respectively; the corresponding SMB-N being 14.896 mg/L and 1.778 mg/L in the summer and the fall respectively. In every season, soil moisture was observed to be lower than the previous season. A maximum soil moisture content of 0.536 g/g and a minimum of 0.008 g/g were recorded in the winter and the fall respectively. The results showed that SMB was not affected by the SMC in the winter and the spring, while SMB was affected by SMC in the summer and the fall. Soil microbes might be limited due to low water availability in the summer and the fall.