Influence of the climate gradient
The aforementioned effect of disturbance on mycorrhizal type distribution was strongest in plots with low mean annual soil temperature as shown in Figure 2 and as indicated by a positive interaction between disturbance and temperature (Table 1). While the percentage of AM vegetation cover was on average higher in roadsides, this pattern tended to be reversed at the upper ranges of the regional temperature gradients where the percentage of AM vegetation cover in high temperature plots was lower in the roadside when compared to the adjacent vegetation, with NM vegetation instead being higher in these roadside plots. This effect was less clear at the inter-regional level: while the effect on disturbance was mostly higher in cold regions compared to warmer regions, both Australia and especially Tenerife where outliers with comparatively high average temperatures as well as a strong effect of road disturbance on the proportion of mycorrhizal association types observed in the vegetation (Fig. 2, Table 3).
Overall, disturbance had larger and more consistent effects on the proportion of mycorrhizal association types than elevation or temperature. Using variation partitioning, we found that disturbance explained 9.8% of the total variation in AM vegetation cover and mean annual soil temperature 4.0%. For EcM, these numbers were 2.8% for disturbance and 2.2% for temperature, for ErM these were 21.6% against 7.9% respectively, and 1.0% against 0.6% for NM. Again, we found similar results when replacing mean annual soil temperature with elevation as the environmental explanatory variable: 8.9% for disturbance and 1.2% for elevation in AM vegetation and respectively 2.7% and 1.9% for EcM, 15.3% and 1.3% for ErM, 3.0% and 1.9% for NM. The direction of the temperature effect on the proportion of mycorrhizal association types also greatly varied across regions for all mycorrhizal types except ErM, while the disturbance effect was consistent in its direction across all regions for all four mycorrhizal types (Table 2).