difference between incubated-N and initial-N (corrected for soil moisture) (Keeney & Nelson,

1982).

Microbial Biomass

 Soil microbial biomass C was determined by chloroform fumigation-extraction (Vance et.

al., 1987), with the following modifications. Twelve grams of soil were sieved from soil samples

stored at 40 C and then placed in 50 ml centrifuge test tubes. Matching 12 g soil samples were

set aside in additional 50 ml centrifuge tubes as the control. The soil samples were fumigated in a

desiccator with 40 ml of alcohol-free chloroform placed into a center beaker, an additional 0.5

ml of chloroform was placed into each centrifuge tube. The top of the desiccator was pressure

sealed and vacated until the chloroform began to boil. The tubes were then incubated for 24

hours at 250C. The dessicator was then opened, resealed, and after the chloroform was reboiled,

incubated for an additional 24 hours.

 The control and fumigated samples were extracted with 36 ml of 0.05 M K2SO4, Shaken

(360 rpm) on an orbital shaker for 1 hour, and centrifuged @ 6000 rpm for 15 minutes. The

supernatant was then filtered through # 42 Whatcom filter papers into 20 ml scintillation vials

and frozen until analysis. Levels of total organic carbon (TOC) were determined on a Shimadzu

TOC-VCSH analyzer (Vance & Entry, 2000). Microbial biomass carbon was calculated as:

[(fumTC ConTC) / 0.51] / (Soil Wt.) = mg C kgl dry wt. soil (Joergensen, 1996). The value of

0.51 is the conversion factor equal to the extractable portion of microbial biomass in a forest soil.

Fumigated and non-fumigated blanks were measured to correct for the chloroform and potassium

persulfate.

 Soil fungal biomass levels were determined by a physical disruption method for extraction

of ergosterol from soil samples (Gong et al. 2001) with the following modifications. Six grams

of soil were mixed with 9 ml of 00C methanol and 1.9 g of glass beads into 20 ml scintillation