E. Gomez et al. Applied Soil Ecology 15 2000 273–281 279
Table 5 Carbon substrates in the Biolog GN microplates that were not
used by one or more locations at the 0–7.5 cm depth S1
S2 S3
S4 Carbohydrates
Adonitol 8 +
a
−
b
+ −
a -d-Lactosa 19
+ +
+ −
b -Methyl-glucoside 25
+ +
+ −
Cellobiose 11 +
+ +
− d
-Melibiose 24 +
+ +
− d-
Raffinose 27 +
+ +
− Gentiobiose 16
+ −
+ −
i-Erythritol 12 +
+ +
− l
-Fucose 14 +
− +
− Lactulose 20
+ +
− −
N-Acetyl-d-galactosamine 6 +
+ +
− Turanose 32
+ −
+ −
Xylitol 33 +
+ −
− Carboxilic acids
a -Hydroxybutiric acid 45
− −
− −
a -Ketobutyric acid 50
+ −
− −
a -Ketovaleric acid 52
+ −
− −
Formic acid 39 +
+ +
− Itaconic acid 49
+ −
+ −
Sebacic acid 58 +
− −
− Amino acids
d -Serine 79
+ +
+ −
Glycyl-l-aspartic acid 70 +
+ +
− Hydroxy-l-proline 73
+ +
+ −
l -Hystidine 72
+ +
+ −
l -Ornithine 75
+ +
+ −
l -Phenylalanine 76
+ +
+ −
l -Threonine 81
+ −
+ −
Aminesamides 2-Amino-ethanol 90
+ −
+ −
Alaninamide 63 +
− −
− Phenyl-ethylamine 88
+ −
+ −
Succinamic acid 61 +
+ +
− Polymer
a -Cyclodextin 1
+ −
+ −
Others 2,3-Butanediol 91
+ −
− −
Thymidine 87 +
+ +
−
a
Indicates OD0.10.
b
Indicates OD0.10.
PC2 differentiated S1 from S3 Fig. 4. More sub- strates than in the surface layer of 0–7.5 cm were me-
tabolized by S2 and S4 in the 7.5–15 cm layer. Mi- crobial communities from S4 assimilated sources 38,
57 and 59 with a high intensity, as they did in the top layer Fig. 5.
Table 6 Carbon substrates in the Biolog GN microplates that were not
used by one or more locations in the depth of 7.5–15 cm S1
S2 S3
S4 Carbohidrates
Adonitol 8 +
a
−
b
+ −
N-Acetyl-d-galactosamine 6 +
− +
+ Xylitol 33
+ +
+ −
Carboxylic acids a
-Hydroxybutyric acid 45 −
− −
− a
-Ketobutyric 50 +
− −
− a
-Ketovaleric acid 52 +
+ −
− Amino acids
l -Ornithine 75
+ +
+ −
l -Phenylalanine 76
+ +
− +
l -Threonine 81
+ −
− +
AminesAmides Alaninamide 63
+ −
− −
Phenyl-ethylamine 88 +
+ −
− Others
Thymidine 87 +
+ +
−
a
Indicates OD0.10.
b
Indicates OD0.10.
The consumption in the amino acid and amineamide guilds seemed to better explain the differences among
S1 and S3. The following substrates were used by S3 at a lower intensity 0.1OD0.25 than by
S1: glycil-l-aspartic acid, glycil-l-glutamic acid, l
-leucine, l
-ornithine, l
-phenilalanine, d
-serine, l
-threonine, 2-amino-ethanol and glucuronamide. Communities from native condition S1 metabo-
lized all the substrates except a-hydroxybutyric acid OD0.10. There were some of the C-sources that
were not used by any of the other locations at both depths. In the 0–7.5 cm deep layer, the largest number
of C-sources that were not assimilated was found in S4. There were less substrates that were not used in
the 7.5–15 cm layer, but the response in the activity on them was more variable among the locations than
in the top layer Tables 5 and 6.
4. Discussion
Some authors could differentiate samples from di- verse locations by means of the sole C-source uti-
lization by the soil bacterial communities. Zak et al. 1994 classified samples coming from a transect with
280 E. Gomez et al. Applied Soil Ecology 15 2000 273–281
different types of vegetation. Lupwayi et al. 1998 could distinguish samples on the basis of tillage and
previous crop. In this study, samples from two layers in the same type of soil, but with different manage-
ments, had different potentials of utilization of the 95 C-sources in Biolog GN assay. The distinctive usage
of those substrates allowed the separation of samples as related to years since clearing of native vegetation
and soil management.
Samples from the native condition S1 showed a larger richness and diversity of metabolized substrates,
thus reflecting a high metabolic potential and func- tional diversity in soil bacterial communities.
The 26-year-clearing location S3 also showed a high consumption on the C-sources, but richness and
diversity indexes were lower in the 0–7.5 cm layer. This is in agreement with the results of Lupwayi et al.
1998, who reported that tillage reduced diversity. However, though diversity was diminished under con-
ventional tillage with respect to the native condition, richness and diversity indexes were larger than in case
of zero tillage. As regards patterns of C-sources uti- lization, S3 metabolized substrates with a high inten-
sity, while differentiating from S1 by a lower activity in compounds with nitrogen in their chemical struc-
ture amino acids, amines and amides. Tillage, partic- ularly moldboard plowing that was the main labor in
S3 for many years, could have enhanced the oxidative potential of microbial communities as a consequence
of soil removal.
The 40-year-clearing location, managed with zero tillage since 1994, had the lower richness and diver-
sity indexes and showed a distinctive pattern of sub- strate utilization. These results are in disagreement
with other findings. Hassink et al. 1991, working in a silty loam soil, did not find that microbial diver-
sity differed in a reduced-input system with respect to a conventional system. Lupwayi et al. 1998 re-
ported more diversity under zero tillage in a sandy loam soil, with respect to conventional management.
As we worked in a soil with a high montmorillonitic clay content, compaction and water retention associ-
ated with zero tillage in this heavy soil could have gen- erated anaerobic conditions that restricted microbial
activity. Linn and Doran 1984 reported that aerobic microbial transformation of C and N can be adversely
affected by the degree of reduction of tillage. The fact that bacterial communities from S4 did not assimi-
late several substrates in the Biolog GN microplates may be indicative of the fact that the species able to
use them were absent. Thus, oxygen restrictions might have produced a shift in microbial populations, favor-
ing those with less efficient anaerobic metabolism.
In the 16-year-clearing location, the more recently cleared and the less disturbed site, diversity was sig-
nificantly affected and patterns of C-source utilization were distinctive from S1 in both the soil layers.
The intensity of use of C-sources has been sug- gested to be strongly influenced by cell density in the
inoculum Haack et al., 1995. In this work, it was found that samples with the largest number of bacteria
per gram of soil S4 in the 0–7.5 cm had the lowest AWCD, richness and diversity. Aliquots from tenfold
dilutions were used both to determine the number of bacteria and to inoculate the Biolog GN microplates.
Hence, the activity on substrates may be related to the growth in the plate Garland and Mills, 1991 more
than to the original density in the sample. Growth, then, would be dependent on the presence of those
bacterial species capable of metabolizing a particular C-source.
5. Conclusions
