Changes in nitrogen-fixing and ammonia-oxidizing bacterial communities in soil of a mixed conifer forest after wildfire.
This study was undertaken to examine the effects of forest fire on two important groups of N-cycling bacteria in soil, the nitrogen-fixing and ammonia-oxidizing bacteria. Sequence and terminal restriction fragment length polymorphism (T-RFLP) analysis of nifH and amoA PCR amplicons was performed on DNA samples from unburned, moderately burned, and severely burned soils of a mixed conifer forest. PCR results indicated that the soil biomass and proportion of nitrogen-fixing and ammonia-oxidizing species was less in soil from the fire-impacted sites than from the unburned sites. The number of dominant nifH sequence types was greater in fire-impacted soils, and nifH sequences that were most closely related to those from the spore-forming taxa Clostridium and Paenibacillus were more abundant in the burned soils. In T-RFLP patterns of the ammonia-oxidizing community, terminal restriction fragments (TRFs) representing amoA cluster 1, 2, or 4 Nitrosospira spp. were dominant (80 to 90%) in unburned soils, while TRFs representing amoA cluster 3A Nitrosospira spp. dominated (65 to 95%) in fire-impacted soils. The dominance of amoA cluster 3A Nitrosospira spp. sequence types was positively correlated with soil pH (5.6 to 7.5) and NH(3)-N levels (0.002 to 0.976 ppm), both of which were higher in burned soils. The decreased microbial biomass and shift in nitrogen-fixing and ammonia-oxidizing communities were still evident in fire-impacted soils collected 14 months after the fire.
Yeager
Chris M
CM
Bioscience Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
Northup
Diana E
DE
Grow
Christy C
CC
Barns
Susan M
SM
Kuske
Cheryl R
CR
D000641:Ammonia / Q000378:metabolism*; D001419:Bacteria / Q000302:isolation & purification / Q000378:metabolism*; D001483:Base Sequence; D005390:Fires; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000235:genetics; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D012987:Soil / Q000032:analysis; D012988:Soil Microbiology; D014197:Trees
D012987:Soil; D000641:Ammonia; D010088:Oxidoreductases; C029130:nitrogenase reductase