Agriculture Reference
In-Depth Information
subsequent analysis of FAME profi les and potential soil enzyme activities
(see below).
13.2.3 MICROBIAL COMMUNITY ANALYSES
MBC and MBN were determined by the chloroform fumigation extraction
method (Vance et al., 1987 and Wu et al., 1990). Organic C was quanti-
fied using a Dohrmann Phoenix 8000 UV-persulfate oxidation analyzer
(Tekmar-Dohrmann, Cincinnati, OH) and organic N was quantified using
alkaline persulfate oxidation (Cabrera and Beare, 1993). No correction
factors were applied. K
2
SO
4
extractable organic carbon (EOC) and nitro-
gen (EON) were calculated as organic C or N, respectively, quantified in
non-fumigated samples (Ros et al., 2009).
Soil microbial community composition was characterized using
FAME profi les. FAME analysis was performed on a 3-g fi eld-moist
equivalent sample using the ester-linked FAME procedure of Schutter
and Dick (2000). FAME analysis was conducted using an Agilent 6890
N gas chromatograph with a 25 m × 0.32 mm × 0.25 μm (5% phenyl)-
methylpolysiloxane Agilent HP-5 fused silica capillary column (Agilent,
Santa Clara, CA) and fl ame ionization detector (Hewlett Packard, Palo Alto,
CA) with ultra-high purity hydrogen as the carrier gas. Absolute amounts
of FAMEs (nmol g
−1
soil) were calculated according to Zelles (1996) us-
ing the 19:0 internal standard and these values were subsequently used to
calculate mol percent by dividing each individual FAME by the total sum of
all FAMEs. Selected FAMEs were used as microbial markers according to
previous research (Zelles, 1999), and included Gram-positive (Gram+) bac-
teria (i15:0, a15:0, i17:0, a17:0), Gram-negative (Gram−) bacteria (cy17:0,
cy19:0), and actinomycetes (10Me16:0, 10Me17:0, 10Me18:0). Fungal
markers included saprophytic fungi (18:1ω9c, 18:2ω6c, and 18:3ω6c) and
AMF (16:1ω5c). FAME 20:4ω6c was used as a marker for soil microfauna
(protozoa and nematodes) and mesofauna (e.g. Collembola) (Stromberger et
al., 2012 and references therein). Bacterial sums were calculated using the
Gram+, Gram−, and actinomycete markers; fungal sums were calculated us-
ing both saprophytic and AMF fungal markers, and the fungal/bacteria ratio
was calculated by dividing the fungal sum by the bacterial sum.
