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Microsite Differentiation Drives the Abundance of Soil Ammonia Oxidizing Bacteria along Aridity Gradients.

Delgado-Baquerizo M, Maestre FT, Eldridge DJ, Singh BK - Front Microbiol (2016)

Bottom Line: Here, we evaluate the abundance of amoA genes from AOB and AOA within six microsites commonly found in drylands (open areas, biocrusts, ant nests, grasses, nitrogen-fixing shrubs, and trees) at 21 sites from eastern Australia, including arid and mesic ecosystems that are threatened by predicted increases in aridity.While the abundance of AOA sharply increased with increasing aridity in all microsites, the response of AOB abundance was microsite-dependent, with increases (nitrogen-fixing shrubs, ant nests), decreases (open areas) or no changes (grasses, biocrusts, trees) in abundance with increasing aridity.These results are linked to particular soil characteristics (e.g., total carbon and ammonium) under these microsites.

View Article: PubMed Central - PubMed

Affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Penrith NSW, Australia.

ABSTRACT
Soil ammonia oxidizing bacteria (AOB) and archaea (AOA) are responsible for nitrification in terrestrial ecosystems, and play important roles in ecosystem functioning by modulating the rates of N losses to ground water and the atmosphere. Vascular plants have been shown to modulate the abundance of AOA and AOB in drylands, the largest biome on Earth. Like plants, biotic and abiotic features such as insect nests and biological soil crusts (biocrusts) have unique biogeochemical attributes (e.g., nutrient availability) that may modify the local abundance of AOA and AOB. However, little is known about how these biotic and abiotic features and their interactions modulate the abundance of AOA and AOB in drylands. Here, we evaluate the abundance of amoA genes from AOB and AOA within six microsites commonly found in drylands (open areas, biocrusts, ant nests, grasses, nitrogen-fixing shrubs, and trees) at 21 sites from eastern Australia, including arid and mesic ecosystems that are threatened by predicted increases in aridity. Our results from structural equation modeling suggest that soil microsite differentiation alters the abundance of AOB (but not AOA) in both arid and mesic ecosystems. While the abundance of AOA sharply increased with increasing aridity in all microsites, the response of AOB abundance was microsite-dependent, with increases (nitrogen-fixing shrubs, ant nests), decreases (open areas) or no changes (grasses, biocrusts, trees) in abundance with increasing aridity. Microsites supporting the highest abundance of AOB were trees, nitrogen-fixing shrubs, and ant nests. These results are linked to particular soil characteristics (e.g., total carbon and ammonium) under these microsites. Our findings advance our understanding of key drivers of functionally important microbial communities and N availability in highly heterogeneous ecosystems such as drylands, which may be obscured when different soil microsites are not explicitly considered.

No MeSH data available.


Related in: MedlinePlus

Changes in the abundance of amoA genes from AOB and AOA across different levels of aridity.(A,B) Show mean ± SE, n = 12 and 9 for arid and mesic ecosystems, respectively. Upper case letters indicate differences between microsites (Tukey post hoc test after ANOVA). When interactions between aridity conditions and microsite were found, we conducted post hoc analyses independently for arid and mesic ecosystems. In this case, lower and upper case letters are used to show microsite differences separately for arid and mesic ecosystems. (C,D) Represent linear regressions between aridity and of the abundance of amoA genes from AOB and AOA across different microsites. The solid and dashed lines in (C,D) represent the fitted linear regressions.
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Figure 2: Changes in the abundance of amoA genes from AOB and AOA across different levels of aridity.(A,B) Show mean ± SE, n = 12 and 9 for arid and mesic ecosystems, respectively. Upper case letters indicate differences between microsites (Tukey post hoc test after ANOVA). When interactions between aridity conditions and microsite were found, we conducted post hoc analyses independently for arid and mesic ecosystems. In this case, lower and upper case letters are used to show microsite differences separately for arid and mesic ecosystems. (C,D) Represent linear regressions between aridity and of the abundance of amoA genes from AOB and AOA across different microsites. The solid and dashed lines in (C,D) represent the fitted linear regressions.

Mentions: The cover of open areas, biocrusts, ant nests, grasses, N-fixing shrubs, and trees ranged from 0–43%, 0–73%, 0–1%, 0–25%, 0–10%, and 0–70%, respectively. The cover of biocrusts increased (ρ = 0.67, P = 0.001), while that of ant nests and trees decreased along the aridity gradient studied (ρant nests = -0.55, P = 0.010; ρtrees = -0.74, P < 0.001). The cover of the remaining microsites did not vary significantly with aridity, though clear trends were observed in some cases (ρbare ground areas = 0.35, P = 0.120; ρgrasses = -0.41, P = 0.064; ρN-fixing shrubs = -0.40, P = 0.069). Our results revealed important differences in the abundance of amoA genes from AOB (but not AOA) among microsites in both arid and mesic ecosystems (Figure 2). Ant nests, N-fixing shrubs and trees showed the highest AOB abundance (Figure 2A). This was particularly evident for ant nests and N-fixing shrubs under the most arid conditions, as indicated by the significant aridity conditions × microsite interaction (P < 0.001; Figure 2A). Thus, this interaction provides evidence that the size effect of microsite on AOB differ between xeric and mesic ecosystems. Biocrusts and open areas had the lowest AOB abundance (Figure 2A), particularly in the arid sites (aridity conditions × microsite interaction: P < 0.001; Figure 2A). We did not find significant differences between microsites for AOA abundance, which consistently showed the highest abundance in the most arid parts of the gradient (P < 0.001; Figure 2B). Interestingly, the abundance of amoA genes from AOA increased with increasing aridity in all microsites (Figure 2D), but the response of AOB to aridity was microsite dependent, with increases (grasses, N-fixing shrubs and ant nests), decreases (open areas) or no changes (biocrusts and trees) in their abundance with increasing aridity (Figure 2C). We found the highest nitrate availability under ant nests, followed by trees and N-fixing shrubs (P < 0.001; Figure 3). Differences between arid and mesic ecosystems were not observed for this variable (P> 0.05; Figure 3).


Microsite Differentiation Drives the Abundance of Soil Ammonia Oxidizing Bacteria along Aridity Gradients.

Delgado-Baquerizo M, Maestre FT, Eldridge DJ, Singh BK - Front Microbiol (2016)

Changes in the abundance of amoA genes from AOB and AOA across different levels of aridity.(A,B) Show mean ± SE, n = 12 and 9 for arid and mesic ecosystems, respectively. Upper case letters indicate differences between microsites (Tukey post hoc test after ANOVA). When interactions between aridity conditions and microsite were found, we conducted post hoc analyses independently for arid and mesic ecosystems. In this case, lower and upper case letters are used to show microsite differences separately for arid and mesic ecosystems. (C,D) Represent linear regressions between aridity and of the abundance of amoA genes from AOB and AOA across different microsites. The solid and dashed lines in (C,D) represent the fitted linear regressions.
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Figure 2: Changes in the abundance of amoA genes from AOB and AOA across different levels of aridity.(A,B) Show mean ± SE, n = 12 and 9 for arid and mesic ecosystems, respectively. Upper case letters indicate differences between microsites (Tukey post hoc test after ANOVA). When interactions between aridity conditions and microsite were found, we conducted post hoc analyses independently for arid and mesic ecosystems. In this case, lower and upper case letters are used to show microsite differences separately for arid and mesic ecosystems. (C,D) Represent linear regressions between aridity and of the abundance of amoA genes from AOB and AOA across different microsites. The solid and dashed lines in (C,D) represent the fitted linear regressions.
Mentions: The cover of open areas, biocrusts, ant nests, grasses, N-fixing shrubs, and trees ranged from 0–43%, 0–73%, 0–1%, 0–25%, 0–10%, and 0–70%, respectively. The cover of biocrusts increased (ρ = 0.67, P = 0.001), while that of ant nests and trees decreased along the aridity gradient studied (ρant nests = -0.55, P = 0.010; ρtrees = -0.74, P < 0.001). The cover of the remaining microsites did not vary significantly with aridity, though clear trends were observed in some cases (ρbare ground areas = 0.35, P = 0.120; ρgrasses = -0.41, P = 0.064; ρN-fixing shrubs = -0.40, P = 0.069). Our results revealed important differences in the abundance of amoA genes from AOB (but not AOA) among microsites in both arid and mesic ecosystems (Figure 2). Ant nests, N-fixing shrubs and trees showed the highest AOB abundance (Figure 2A). This was particularly evident for ant nests and N-fixing shrubs under the most arid conditions, as indicated by the significant aridity conditions × microsite interaction (P < 0.001; Figure 2A). Thus, this interaction provides evidence that the size effect of microsite on AOB differ between xeric and mesic ecosystems. Biocrusts and open areas had the lowest AOB abundance (Figure 2A), particularly in the arid sites (aridity conditions × microsite interaction: P < 0.001; Figure 2A). We did not find significant differences between microsites for AOA abundance, which consistently showed the highest abundance in the most arid parts of the gradient (P < 0.001; Figure 2B). Interestingly, the abundance of amoA genes from AOA increased with increasing aridity in all microsites (Figure 2D), but the response of AOB to aridity was microsite dependent, with increases (grasses, N-fixing shrubs and ant nests), decreases (open areas) or no changes (biocrusts and trees) in their abundance with increasing aridity (Figure 2C). We found the highest nitrate availability under ant nests, followed by trees and N-fixing shrubs (P < 0.001; Figure 3). Differences between arid and mesic ecosystems were not observed for this variable (P> 0.05; Figure 3).

Bottom Line: Here, we evaluate the abundance of amoA genes from AOB and AOA within six microsites commonly found in drylands (open areas, biocrusts, ant nests, grasses, nitrogen-fixing shrubs, and trees) at 21 sites from eastern Australia, including arid and mesic ecosystems that are threatened by predicted increases in aridity.While the abundance of AOA sharply increased with increasing aridity in all microsites, the response of AOB abundance was microsite-dependent, with increases (nitrogen-fixing shrubs, ant nests), decreases (open areas) or no changes (grasses, biocrusts, trees) in abundance with increasing aridity.These results are linked to particular soil characteristics (e.g., total carbon and ammonium) under these microsites.

View Article: PubMed Central - PubMed

Affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Penrith NSW, Australia.

ABSTRACT
Soil ammonia oxidizing bacteria (AOB) and archaea (AOA) are responsible for nitrification in terrestrial ecosystems, and play important roles in ecosystem functioning by modulating the rates of N losses to ground water and the atmosphere. Vascular plants have been shown to modulate the abundance of AOA and AOB in drylands, the largest biome on Earth. Like plants, biotic and abiotic features such as insect nests and biological soil crusts (biocrusts) have unique biogeochemical attributes (e.g., nutrient availability) that may modify the local abundance of AOA and AOB. However, little is known about how these biotic and abiotic features and their interactions modulate the abundance of AOA and AOB in drylands. Here, we evaluate the abundance of amoA genes from AOB and AOA within six microsites commonly found in drylands (open areas, biocrusts, ant nests, grasses, nitrogen-fixing shrubs, and trees) at 21 sites from eastern Australia, including arid and mesic ecosystems that are threatened by predicted increases in aridity. Our results from structural equation modeling suggest that soil microsite differentiation alters the abundance of AOB (but not AOA) in both arid and mesic ecosystems. While the abundance of AOA sharply increased with increasing aridity in all microsites, the response of AOB abundance was microsite-dependent, with increases (nitrogen-fixing shrubs, ant nests), decreases (open areas) or no changes (grasses, biocrusts, trees) in abundance with increasing aridity. Microsites supporting the highest abundance of AOB were trees, nitrogen-fixing shrubs, and ant nests. These results are linked to particular soil characteristics (e.g., total carbon and ammonium) under these microsites. Our findings advance our understanding of key drivers of functionally important microbial communities and N availability in highly heterogeneous ecosystems such as drylands, which may be obscured when different soil microsites are not explicitly considered.

No MeSH data available.


Related in: MedlinePlus