Figure 3. Biplot representations of the results of PCA and RDA analyses.

(a) PCA performed on the matrix with plant growth parameters and shoot nutrients content. RDA performed on the matrix of plant growth parameters and shoot nutrients content constrained by the matrix of bacterial inoculation treatments, either in (b) the cohort of plants singly inoculated with different strains of Micromonospora spp. and in (c) the cohort of plants co-inoculated with Micromonospora and E. meliloti 1021. Open circles represent the centroids of the treatments inoculated singly with each of the fifteen Micromonospora strains while full circles represent those of the treatments also inoculated with E. meliloti 1021. Star symbols represent the centroids of the control treatments without any microbial inoculation (open star) and inoculated with E. meliloti 1021 only (full star). Arrows represent variables measured on individual alfalfa plants: shoot dry weight (Sdw), root dry weight (Rdw), shoot to root ratio (S:R), number of nodules (Nod); and shoot contents of carbon (C), nitrogen (N), phosphorus (P), and potassium (K). The variable Nod is passively projected into the PCA diagram (a) but it was not included in the calculation (dotted arrow). Values on the axes indicate percentages of total variation explained by each axis and P-values of significance for the RDA canonical axes (b and c) obtained by Monte Carlo permutation tests (999 permutations).