We then sought to relate the observed patterns of community composition
to the environmental variables. The distLM analysis identified the
particle size (clay, silt and sand), pH, soil humidity, and some
nutrients (nitrogen, phosphorus, calcium and magnesium) to be the best
predictors of the bacterial and fungal community composition (Figure
XX). The model successfully explains the main trends of the bacterial
and fungal variance displayed in the constrained ordination (Figure XX).
As depicted by the fungal dbRDA, particles size (clay, silt and sand),
humidity, pH, calcium and phosphorus clearly discriminate the fungal
communities between the silt and the sand site. The
discrimination between the organic and conventional
farming, however, is not obvious: magnesium seems to be the best
variable to separate conventional from organic farming.
Regarding the bacterial dbRDA, there was also a clear discrimination
between the silt and sand site mainly drove by the
particle size (clay, silt and sand) and humidity. Here, pH, calcium and
phosphorus were good predictors of organic farming at the
silt site, while magnesium seems here again to be the best to
separate conventional from organic farming.