Community composition of soil organisms under different wheat-farming systems - Microbial Ecology in Sustainable Agroecosystems - page 99

(a) 18:1ω7
(b) NLFA 16:1ω5
(c) gram-
negative
Figure 5.3 Two-dimensional NMDS ordination based on concentrations of 17 fatty acids in 16 plots
of biodynamic, bioorganic, conventional with farmyard manure or conventional only with mineral
fertilizer (stockless farming) farming systems (see Table 5.1 ; 2-D stress = 0.084). Bubble sizes are scaled
according to the data range and superimposed based on concentrations of (a) 18:1ω7 (biomarker for
gram-negative bacteria, data range = 0.091-0.118 mol%), (b) NLFA 16:1ω5 (biomarker for AMF, 0.035-
0.052 mol%), and (c) combined biomarker FAs for gram-negative bacteria (0.191-0.233 mol%).
between communities of all farming systems with the exception of BIODYN versus
BIOORG. The genus that contributed most to the observed differences between CONMIN
and BIODYN or BIOORG was the plant and hyphal feeder Tylenchus , which was almost
absent from CONMIN soils ( Figure 5.4a ). The genus Rhabditis, which encompasses bacteri-
vores, further discriminated CONFYM from BIODYN, BIOORG, and CONMIN nematode
communities as individuals from this genus were common in CONFYM but absent from
the other systems ( Figure 5.4b ) . At the family level, nematode communities also differed
between farming systems ( R = 0.508; P = 0.001), but at this taxonomic resolution, family
composition in BIOORG did not differ from BIODYN or from CONFYM. The fungal feeding
Aphelenchidae were absent from BIODYN but abundant in the other systems ( Figure 5.4c ) .
In contrast, Anguinidae, which are considered plant or fungal feeders, occurred at much