Fig 1.
Sampling sites from across New Zealand and the Whangara farm (call out box).
The Pouawa and Rotomanu sites, where spatially-dense sampling was conducted a single field, are labelled (star symbols). Location data (GPS) and soil type information can be found in the Supplementary Information, S1 Table.
Fig 2.
(A) Rhizobium leguminosarum bv. trifolii population size and (B) nitrogen fixing effectiveness (symbiotic potential relative to commercial Rlt strain TA1) in soils across different spatial scales. Boxes show median values and extend to the 25th to 75th percentiles. For 2B, the dashed line at 100% symbiotic potential = white clover growth when inoculated with the commercial rhizobia inoculant strain TA1. Treatments sharing the same lettering (a or b) have similar treatment means (Bonferroni comparison of means; α = 0.05).
Fig 3.
Spatial variation in Rhizobium leguminosarum bv. trifolii population size, (most probable number) based on nodule formation on Trifolium repens cv. Tribute.
Black dots represent sampling spots based on GPS-marked points. Contour lines for Whangara and Pouawa are given; the field at Rotomanu had flat topography. MPN variation between samples was assessed using the RBK method in ARC-GIS.
Fig 4.
Spatial variation in Rhizobium leguminosarum bv. trifolii symbiotic potential (SP); i.e. efficacy at increasing the growth of Trifolium repens cv. Tribute.
Assay conditions for clover growth had minimal nitrogen content, such that plant growth was directly related to N-fixation occurring through symbiosis. SP is calculated relative to growth of T. repens c.v Tribute inoculated with the current commercial R. leguminosarum bv. trifolii strain used in New Zealand, TA1 (= 100%). Black dots represent sampling spots based on GPS-marked points. Contour lines for Whangara and Pouawa are given; the field at Rotomanu had flat topography. Variation in SP between samples was assessed using the RBK method in ARC-GIS.
Fig 5.
Relationship between the R. leguminosarum bv. trifolii population size and symbiotic potential of the legume-rhizobia symbiosis in 50 samples of soils collected from within a single field at Pouawa (hill country sheep and beef farm).
Solid line is the linear regression model fit; dashed lines are the 95% confidence intervals.
Fig 6.
Venn diagrams showing similarity in properties of soils, at different spatial sampling scales, that have significant correlations with Rhizobium leguminosarum bv. trifolii population size (MPN’s; 6A), and symbiotic potential (6B).
Table 1.
Summary of Pearson’s correlations between Rhizobium leguminosarum bv. trifolii populations size (MPN values) and symbiotic potential with soil physicochemical properties in samples with different geographic ranges.