Discussion

\label{discussion}
  1. 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).
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.)