Nitrate production was 13.8 mg-1 NO3 / kg soil during April 2002 and 135.7 mg-l NO3 / kg soil

during August 2002. In comparison, Nitrate production was 4.7 mg-l NO3 / kg soil during April

2005 and 1.9 mg-l NO3 / kg soil during August 2005 (Table 3-3; Figure 5-3, Chapter 5).

Ammonium production was 13.4 mg-l NH4 / kg soil during April 2002 and 104.7 mg-l NH4 / kg

soil during August 2002. During 2005, ammonium production was 8.9 mg-l NH4 / kg soil during

April and 9.6 mg-l NH4 / kg soil during August (Table 3-3).

 Nmin was positively related to ammonification (NH4 ) (r > 0.810; p < 0.0001) during all

three age classes, but not correlated with nitrification. Nmin became positively correlated with

soil moisture and SOM (r > 0.460 (p < 0.01) during the mid-aged class and remained so through

the mature age class (Table 3-4). Ammonium production was negatively related to nitrate

production (NO3-) during the mid-age and mature (r = 0.470; p < 0.001) age classes (Table 3-3).

Microbial Properties

 Mean soil microbial biomass carbon (Cmb) lCVOIS were 275 (mg C / kg soil) for the young

age stands, 416 (mg C / kg soil) during the mid-aged class, and 339 (mg C / kg soil) during the

mature age class for the reference sites (Table 3-2). Mean soil fungal biomass carbon (Cfb) levels

were 102 (mg C / kg soil) for the young age class, 163 (mg C / kg soil) for the mid-aged stands,

and 125 (mg C / kg soil) during the mature age class at the reference sites (Table 3-2). Fungal

biomass carbon increased during the first 60 years (~200 mg C / kg soil), then decreased down to

110 years (~100 mg C / kg soil; Figure 3-6). The fungal-to-microbial biomass ratio (FB-to-MB)

decreased from a mean value of 0.4 to 0.2 during the first fifteen years after establishment, and

then increased to 0.8 at 50 years (Figure 3-7). Microbial biomass (Cmb) had a negative

relationship (r > 0.400 (p < 0.01) with soil pH during the mid-aged and mature age classes

(Table 3-3).