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Archaeal Ammonia Oxidizers Dominate in Numbers, but Bacteria Drive Gross Nitrification in N-amended Grassland Soil.

Sterngren AE, Hallin S, Bengtson P - Front Microbiol (2015)

Bottom Line: The aim of this experiment was to test the hypotheses that high nitrogen availability would favor AOB and result in high gross nitrification rates, while high carbon availability would result in low nitrogen concentrations that favor the activity of AOA.The abundance of amoA genes from AOB increased markedly in treatments that received nitrogen, suggesting that AOB were the main ammonia oxidizers here.However, AOB could not account for the entire ammonia oxidation activity observed in treatments where the soil was deficient in available nitrogen.

View Article: PubMed Central - PubMed

Affiliation: Microbial Ecology, Department of Biology, Lund University Lund, Sweden.

ABSTRACT
Both ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) play an important role in nitrification in terrestrial environments. Most often AOA outnumber AOB, but the relative contribution of AOA and AOB to nitrification rates remains unclear. The aim of this experiment was to test the hypotheses that high nitrogen availability would favor AOB and result in high gross nitrification rates, while high carbon availability would result in low nitrogen concentrations that favor the activity of AOA. The hypotheses were tested in a microcosm experiment where sugars, ammonium, or amino acids were added regularly to a grassland soil for a period of 33 days. The abundance of amoA genes from AOB increased markedly in treatments that received nitrogen, suggesting that AOB were the main ammonia oxidizers here. However, AOB could not account for the entire ammonia oxidation activity observed in treatments where the soil was deficient in available nitrogen. The findings suggest that AOA are important drivers of nitrification under nitrogen-poor conditions, but that input of easily available nitrogen results in increased abundance, activity, and relative importance of AOB for gross nitrification in grassland soil.

No MeSH data available.


Related in: MedlinePlus

Relationship between log-transformed AOA:AOB amoA gene ratios and gross nitrification rates in (A) treatments where nitrogen was added (amino acids and ammonium; r = 0.97, p = 0.001) and (B) treatments where no nitrogen was added (sugar and control; r = 0.91, p = 0.013).
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Figure 2: Relationship between log-transformed AOA:AOB amoA gene ratios and gross nitrification rates in (A) treatments where nitrogen was added (amino acids and ammonium; r = 0.97, p = 0.001) and (B) treatments where no nitrogen was added (sugar and control; r = 0.91, p = 0.013).

Mentions: In general, gross nitrification rates increased during the cause of the experiment (F = 156.72, p < 0.001). The largest increase and the highest nitrification rates were found in the ammonium treatment (Table 1). The approximately eightfold increase in gross nitrification between the first and the last sampling in the ammonium treatment corresponded to the increase in bacterial amoA copy numbers (approximately sixfold, Figure 1B). Similarly, the threefold increase in nitrification rates in the amino-acid treatment corresponded with the increase in bacterial amoA copy numbers of similar magnitude (from 1.4 × 106 to 4.2 × 106 copies per g dry soil, Figure 1B). Accordingly, there was a significant negative relationship between the AOA:AOB amoA gene ratio and the gross nitrification rate in the microcosms where nitrogen was added (p = 0.001; Figure 2A). By contrast, we found a positive relationship between the ratio of AOA:AOB amoA genes and the gross nitrification rate in treatments that did not receive nitrogen (p = 0.013; Figure 2B). These findings suggest that AOB dominated nitrification in the treatments where nitrogen was added, and that the relative contribution of AOA to nitrification was higher in the treatments not receiving nitrogen, in which the ammonium concentration remained low [<4 μg N (g dry soil)-1] throughout the experiment (Table 1).


Archaeal Ammonia Oxidizers Dominate in Numbers, but Bacteria Drive Gross Nitrification in N-amended Grassland Soil.

Sterngren AE, Hallin S, Bengtson P - Front Microbiol (2015)

Relationship between log-transformed AOA:AOB amoA gene ratios and gross nitrification rates in (A) treatments where nitrogen was added (amino acids and ammonium; r = 0.97, p = 0.001) and (B) treatments where no nitrogen was added (sugar and control; r = 0.91, p = 0.013).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4663241&req=5

Figure 2: Relationship between log-transformed AOA:AOB amoA gene ratios and gross nitrification rates in (A) treatments where nitrogen was added (amino acids and ammonium; r = 0.97, p = 0.001) and (B) treatments where no nitrogen was added (sugar and control; r = 0.91, p = 0.013).
Mentions: In general, gross nitrification rates increased during the cause of the experiment (F = 156.72, p < 0.001). The largest increase and the highest nitrification rates were found in the ammonium treatment (Table 1). The approximately eightfold increase in gross nitrification between the first and the last sampling in the ammonium treatment corresponded to the increase in bacterial amoA copy numbers (approximately sixfold, Figure 1B). Similarly, the threefold increase in nitrification rates in the amino-acid treatment corresponded with the increase in bacterial amoA copy numbers of similar magnitude (from 1.4 × 106 to 4.2 × 106 copies per g dry soil, Figure 1B). Accordingly, there was a significant negative relationship between the AOA:AOB amoA gene ratio and the gross nitrification rate in the microcosms where nitrogen was added (p = 0.001; Figure 2A). By contrast, we found a positive relationship between the ratio of AOA:AOB amoA genes and the gross nitrification rate in treatments that did not receive nitrogen (p = 0.013; Figure 2B). These findings suggest that AOB dominated nitrification in the treatments where nitrogen was added, and that the relative contribution of AOA to nitrification was higher in the treatments not receiving nitrogen, in which the ammonium concentration remained low [<4 μg N (g dry soil)-1] throughout the experiment (Table 1).

Bottom Line: The aim of this experiment was to test the hypotheses that high nitrogen availability would favor AOB and result in high gross nitrification rates, while high carbon availability would result in low nitrogen concentrations that favor the activity of AOA.The abundance of amoA genes from AOB increased markedly in treatments that received nitrogen, suggesting that AOB were the main ammonia oxidizers here.However, AOB could not account for the entire ammonia oxidation activity observed in treatments where the soil was deficient in available nitrogen.

View Article: PubMed Central - PubMed

Affiliation: Microbial Ecology, Department of Biology, Lund University Lund, Sweden.

ABSTRACT
Both ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) play an important role in nitrification in terrestrial environments. Most often AOA outnumber AOB, but the relative contribution of AOA and AOB to nitrification rates remains unclear. The aim of this experiment was to test the hypotheses that high nitrogen availability would favor AOB and result in high gross nitrification rates, while high carbon availability would result in low nitrogen concentrations that favor the activity of AOA. The hypotheses were tested in a microcosm experiment where sugars, ammonium, or amino acids were added regularly to a grassland soil for a period of 33 days. The abundance of amoA genes from AOB increased markedly in treatments that received nitrogen, suggesting that AOB were the main ammonia oxidizers here. However, AOB could not account for the entire ammonia oxidation activity observed in treatments where the soil was deficient in available nitrogen. The findings suggest that AOA are important drivers of nitrification under nitrogen-poor conditions, but that input of easily available nitrogen results in increased abundance, activity, and relative importance of AOB for gross nitrification in grassland soil.

No MeSH data available.


Related in: MedlinePlus