2.3 Soil microbial community analysis
The soil microbial community was determined by analyzing the phospholipid fatty acids (PLFAs), which were extracted and quantified from 8.0 g of dry soils using a procedure described by (Bossio et al. 1998). A 19:0 methyl ester internal standard was used to calculate the PLFA concentrations. The a13:0, i14:0, i15:0, i16:0, i17:0 and a17:0 fatty acids were chosen to represent PLFAs from gram-positive (Gram+) bacteria (Frostegard et al. 1996), and the 16:1ω7c, 17:1ω8c, 18:1ω5c, 18:1ω9t, 17:0cy and 19:0cy fatty acids were chosen to represent PLFAs from gram-negative (Gram-) bacteria (Frostegard et al. 1996). The 18:2ω6c and 18:2ω9c fatty acid was chosen to represent the fungal biomass PLFA (Frostegard et al. 1993; Kaur et al. 2005), and 16:1ω5c was used as an indicator of arbuscular mycorrhizal fungi (AMF) (Olsson 1999). The 10 Methyl 16:0, 10 Methyl 17:0 and 10 Methyl 18:0 fatty acids were chosen to represent actinomycete (Act) (Frostegard et al. 1996). The PLFA fungal to bacterial ratio (F:B ratio) and Gram positive bacteria to Gram negative bacteria ratio (Gp:Gn ratio) was calculated to estimate the relative abundance of these two groups (Frostegard et al. 1996), and the total fatty acid percentages for each microbial group described above were calculated to represent their relative contributions to the total microbial biomass.