Figure 2.

Effect of abiotic factors on the plant and bacterial communities. (A) General effect of abiotic factors on the plant community structure, determined from the cover-abundance at each site and the environmental variables within NMDS ordination space using envfit(), and using previously published data^30,36,40. Arrows indicate relative degree and directionality of effect. ST, soil temperature at depth −5 cm; pH, soil pH; C13, stable isotopic carbon ratio (mL⁻¹ vs VPDB); N15, stable isotopic nitrogen ratio (mL⁻¹ vs N₂ in air); H, bulk hydrogen content (wt %); N, bulk nitrogen content (wt %); CN, C:N ratio; HI, hydrogen index (mg HC g⁻¹ TOC); OI, oxygen index (mg CO₂ g⁻¹ TOC); TOC, total organic carbon content (wt %); MiC, mineral carbon content (wt %); BSW, bulk soil gravimetric water content (40°, %); GSW, sieved soil gravimetric water content (105 °C, %); Si, SiO₂ (wt %); Mn, MnO content (wt %); Ca, CaO content (wt %); Na, Na₂ content (wt %); PSi, phyllosilicates (%); Pla, plagioclase-Na (%); Cal, calcite (%); Lon, longitude (x, Swiss coordinate system); Lat, latitude (y); Alt, elevation (m); slop, terrain slope (°); aspv, sine transformed direction that a slope faces; top, topographic position; deg, annual degree days (day × deg); min, monthly moisture index (0.1 mm month⁻¹); srd, daily average of global potential shortwave radiation per month (kJ day⁻¹); tav, monthly average temperature (°C × 100); swb, annual average site water balance accounting for soil properaties (0.1 mm year⁻¹); sfro, annual average number of frost days during the growing season (day × 100); pda, number of precipitation days per growing season (day); prc, monthly mean precipitation sum (mm). (B) Plant species richness and (C) bacterial OTU richness at each site plotted against soil pH. The dots are color-coded a posteriori according to the vegetation alliance to which the sites belong. Lines in panels B and C display quadratic trend-lines with their adjusted R² (Rsq) and P-values.