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(a)
2
a
c
c
b
ab
1.5
1
0.5
0
0
1
5
10
30
(b)
3.5
3
2.5
2
1.5
d
ab
a
bc
c
1
0.5
0
0
1
5
10
30
(c)
1
a
cd
d
bc
b
0.5
0
0
1
5
10
30
Figure 1.5
The effect of age in conservation tillage in cotton fields in southern Georgia on (a) bac-
terial-to-fungal ratios as measured by FAME biomarkers; (b) arbuscular mycorrhizal fungi (AMF)
expressed as the relative percentage mole fraction of 16:1ω5c; and (c) an indicator of microbial stress,
cy17:0: 16:1ω7c, from soils (0-5 cm depth) at five sites across a chronosequence of conservation till-
age. Data shown include standard error; different letters denote significant differences at
P
< 0.05
(Tukey's). (From Simmons, B.L. and D.C. Coleman. 2008. Microbial community response to transi-
tion from conventional to conservation tillage in cotton fields.
Applied Soil Ecology
40:518-528. With
permission from Elsevier.)
Thus, there were more ciliates, flagellates, and amoebae in the older fields (
Figure 1.6
;
Adl
et al, 2006); microarthropods were more speciose but had lower total biomass in the older
fields as well (Adl et al., 2006). This amplification of species diversity effects in the detriti-
vore fauna compared to the microbial diversity was unexpected.
In our agroecosystem chronosequence study, the microbial biodiversity patterns
did not conform to the proposed fungal/bacterial changes as proposed by Harris (2009;
Figure 1.7
)
. However, the faunal changes showed a greater response to the changes in man-
agement and organic matter levels. With the marked oscillations in SOM between spring
and fall sampling seasons over the 2 y of this study, it is probably safest to consider these
trends as on the margins of significant effects. In contrast, a comparative study of micro-
bial diversities in conventional tillage, no-tillage, and forested ecosystems adjacent to the
Horseshoe Bend Long-Term Research study in bottomlands near Athens, Georgia, micro-
bial diversity, as measured by 16S rRNA genes, was greater in the agricultural fields than
in the nearby forest (Upchurch et al., 2008). These trends seemed to be correlated with the
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