The labile C pool, however, is scarce for microbial growth in most bulk soils (Blagodatsky and Richter, 1998; Weintraub and Schimel, 2003)and therefore, microbial biomass will decrease under nutrient addition(Ramirez et al., 2012). Moreover, nutrient addition (or the use of fertilizers) may reduce soil pH, and subsequently affect soil microbial activity and soil CO2 emission (Rousk et al., 2010; Yoshitake et al.,2007). Positive relationships between soil pH and microbial biomass are well established and microbial biomass may be lower in acidic soils owing to the direct effects of decreased pH on microbial biomass(Wardle, 1992, Treseder, 2008).