Discussion
\label{discussion}
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soil texture influence communities:
de Vries (2012) ⇒ As reported by de Vries (2012), soil texture,
in the form of silt percentage, explained variation in microbial
biomass. Finely textured
soils are known to be more favourable for bacterial growth, because
of their greater water holding capacity and nutrient availability, and
better protection from bacterial grazers; accordingly, a positive
relationship
between soil texture and bacterial biomass has been observed at field
(Johnson et al. 2003) and landscape scales (Fierer
proposed
that fungi are associated with the particulate organic matter of the
coarser sand fraction (Sessitsch et al. 2001).
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Our findings identify the site, defined by different soil
texture, as the main driver of microbial beta-diversity, explaining a
large part of the microbial community variability (34% and 20% for
bacteria and fungi). The overall change in the community composition was
also accompanied by an overall increase of fungal richness at the
sand site (Figure XX), while no overall site effect was
observed for the bacterial richness. Several studies identified the soil
texture (particle size) as a key factor determining bacterial and fungal
community diversity (Sessitsch et al. 2001, Girvan et al., 2003, wakelin
et al., 2008). Finer size particles (silt and clay) generally support
larger and more diverse bacterial communities as they provide a
protective habitat as the small pores exclude predators such as
protozoa. In our study, the textural contrast between the both site
could not be enough to detect an impact on the bacterial richness. How
to explain the higher fungal richness in the sand soil?
Our findings also identify the farming system as the second driver of
microbial community diversity.
As mentioned by Girvan et al. (2003), the underlying soil chemistry and
structure primarily determine the bacterial community composition.
More interestingly, our findings highlight a farming system
effect on microbial community diversity (Figure XX).
The fungal richness and evenness
The change in the community composition
Our results are partially consistent with those from Sessitsch et al.
(2001)
reported a strong particle size effect on the microbial community
structure.
More importantly is the fact that the magnitude of microbial communities
response to farming system change according the site.
and the farming system as the main drivers of microbial
beta-diversity (Figure XX). More specifically, we also identified a
strong interaction of the farming system with the site, as
well as with the the spatial component (plot) assuming that the
magnitude of microbial response to the farming system differs
from the soil texture but also from the spatial location. Here, we
detected a stronger farming system effect on microbial
beta-diversity in the silt soil, characterized by a higher
chemical fertility, humidity and a lower acidity than the sand
soil (Figure XX).
As the structural organization of soil particles (clay, silt, sand) in
association with the organic matter is strongly associated with the
formation of habitat for microorganisms, soils harboring different
proportion of soil particles are expected to modify the microbial
structure (Sessitsch et al., 2001).
DIVERS:
(The CAP analysis identify in average more distinct bacterial
communities among the conventional plots (6% of
mis-classification error) than among the organic plots (28% of
mis-classification error), while no major influence was detected on the
fungal communities. These results suggest a higher similarity of
bacterial communities among the organic plots than among the
conventional ones.)