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.