TABLE 1.
Abundance of fungal nirK (fnirK) and fungal 18S rRNA genes (18S) in terrestrial biomes at Level 3a
| Biomes at Level 3 (n) | Fungal nirK (10−7) | Fungal 18S (10−7) | fnirK:18S (%) | fnirK:pnirK (%) |
|---|---|---|---|---|
| Boreal forests and taiga (59) | 3.5 ± 2.9 bcd | 412 ± 296 b | 1.6 ± 2.1 f | 1.7 ± 1.4 b |
| Temperate coniferous forests (224) | 3.4 ± 2.9 bc | 282 ± 364 c | 2.7 ± 2.8 de | 1.5 ± 1.3 b |
| Temperate broadleaf and mixed forests (417) | 3.5 ± 2.9 bc | 227 ± 217 cd | 3.2 ± 4.4 d | 1.5 ± 1.3 bc |
| Mediterranean forests, woodlands, and shrublands (60) | 2.1 ± 1.1 def | 269 ± 234 bcd | 1.4 ± 1.4 ef | 1.0 ± 0.7 cd |
| Tropical and subtropical dry broadleaf forests (28) | 2.9 ± 1.6 bcde | 87 ± 107 ef | 0.8 ± 12.8 b | 0.6 ± 0.4 cd |
| Tropical and subtropical moist broadleaf forests (37) | 4.7 ± 3.8 b | 194 ± 193 cd | 3.9 ± 4.0 bcd | 1.6 ± 1.2 bc |
| Temperate grasslands, savannas, and shrublands (116) | 3.3 ± 3.6 bcd | 78 ± 76 e | 7.2 ± 9.7 bc | 0.9 ± 1.2 d |
| Tropical and subtropical grasslands, savannas, and shrublands (34) | 3.0 ± 3.2 bcdef | 153 ± 198 cde | 4.3 ± 6.6 cd | 1.2 ± 1.4 bcd |
| Deserts and xeric shrublands (72) | 2.6 ± 2.8 def | 82 ± 89 e | 9.2 ± 19.6 bc | 0.8 ± 0.7 d |
| Tundra (63) | 1.9 ± 1.6 f | 45 ± 46 f | 9.2 ± 11.7 b | 1.4 ± 1.1 bc |
| Croplands (140) | 2.5 ± 1.3 cde | 115 ± 126 e | 7.3 ± 10.1 bc | 0.4 ± 0.3 e |
| Rhizosphere (235) | 2.2 ± 2.0 ef | 146 ± 104 d | 2.1 ± 2.8 de | 0.3 ± 0.3 e |
a
The fungal nirK fragment counts were normalized by the total number of reads in the corresponding metagenome and were also standardized to the fungal 18S rRNA gene abundance (fnirK:18S) as well as that of the prokaryotic nirK (pnirK; fnirK:pnirK) (mean ± SD, n = 28 to 417). The number of metagenomes is shown in parentheses for each biome. The superscript letters indicate significant differences across biomes (P < 0.05).