Agriculture Reference
In-Depth Information
studies suggested long-term effects of plants on microbial communities in
bulk soils [16]. Long-term agricultural use impacts soil physicochemical
characteristics [3], [16], [17], and thus probably alters the composition and
properties of biogeochemical interfaces in soils [51].
The present study showed that agricultural use impacted several bacte-
rial phyla in the soils of the sites studied, e.g.,
Acidobacteria, Chlorofl exi,
Spirochaetes, Verrucomicrobia, Gemmatimonadetes, Deltaproteobacteria
(
Proteobacteria
),
Acidimicrobiales
(
Actinobacteria
) and
Rubrobacterales
(
Actinobacteria
).
Acidobacteria
have been found to be dominant in sev-
eral soils [52] though often they are diffi cult to cultivate. In the study by
Bisette et al. [16], the proportion of
Acidobacteria
was found increased
in grassland soils compared to soils under agricultural use at one site in
Australia. Compared with agricultural soils, their relative abundance was
also reported to be higher in forest, desert or prairie soils [52], [53]. The
proportion of
Acidobacteria
was reported to be signifi cantly lower in
nutrient-rich rhizosphere than in bulk soil, confi rming their oligotrophic
lifestyle [54]. Under dry conditions, the net primary productivity of plants
is controlled by water [55], [56]. Additional water supply in the alfalfa
fi elds enhanced plant growth and probably elevated the extent of plant
exudates into soil over a time period of about 50 years. Recently the rela-
tive abundance of
Acidobacteria
was found to be negatively correlated
with the level of nitrogen input (fertilizer) [57], which in general increases
the net productivity of vegetation.
Chlorofl exi
also was reported to prevail
in nutrient poor soils [52], [58] and other oligotrophic ecosystems such as
soils from high-elevation regions where vegetation is patchy [59], alpine
tundra soil [60] or hyperarid polar desert soil [61]. A few bacteria belong-
ing to
Chlorofl exi
which could be retrieved from soil had very slow rates
of growth and mini-colony formation [62], [63] which are typical charac-
teristics of oligotrophic organisms. In accordance with the present study,
Fierer et al. [57] showed that the relative abundance of
Chlorofl exi
was
also lower in the plots with high levels of nitrogen input.
In the present study, the physicochemical analysis of the soils done for
four independent replicates per site and treatment revealed that the con-
centration of sulphate (probably due to fertilization) was higher in alfalfa
soils. Sulphate can be used as terminal electron acceptor by some anaero-
bic bacteria. However, a high proportion of OTUs belonging to
Desul-
