FIG 4.

Spearman ranked correlations of fungal nirK abundance as well as the ratio to 18S rRNA gene abundance (fnirK:18S) and prokaryotic nirK (fnirK: pnirK) with edaphic variables. Correlations are shown for all terrestrial biomes and for five terrestrial biomes at Level 2. Rhizosphere metagenomes were not included due to the absence of associated metadata. The correlations are colored if significant (P < 0.05), according to their strength, with red for negative correlations and blue for positive correlations. Nonsignificant correlations are colored in gray. Those not determined due to an insufficient sample number (n < 25) are marked with an asterisk. Sample sizes differed among metagenomes, as indicated in Table S2. SOC, soil organic carbon; C:N, total carbon to total nitrogen ratio; N, total nitrogen; NH₄⁺, ammonium; NO₃⁻, nitrate; moisture, soil moisture; clay, soil clay content; Cu, soil copper content; pH, soil pH measured in CaCl₂. NO₃⁻ in tundra soils was reported in μM.