Abstract
Abstract Ground‐level ozone (O 3 ) pollution frequently coincides with the deposition of anthropogenic nitrogen (N), and both factors can influence the structure and functionality of both above‐ and belowground ecosystems. Elevated O 3 levels have been shown to adversely impact plants in many prior reports, but the interacting effects of high O 3 levels and N addition on exposed plants remain to be clearly defined, and the changes in rhizosphere microbial community composition in this context have yet to be studied. The direct and indirect mechanisms and interactions among plants, microbes, and the soil that shape these O 3 and N responses are also poorly understood. Herein, we explored the interactive effects of O 3 exposure (five levels) and soil N (four levels) on the composition of rhizosphere soil microbial communities associated with poplar trees ( Populus euramericana cv. ‘74/76’). In these analyses, exposure to higher levels of O 3 was linked to significant decreases in bacteria, fungi, arbuscular mycorrhizal fungi, and to a reduction in the ratio of fungi‐to‐bacteria, whereas soil N addition had no impact on these parameters. No interactive effects between O 3 and N were observed in the context of alterations in soil microbial community composition, and equivalent performance was observed for concentration‐based (AOT40, cumulative exposure to hourly O 3 concentrations >40 ppb) and flux‐based [POD 1 and POD 7 , cumulative stomatal uptake of O 3 > 1 or 7 nmol O 3 m −1 PLA (projected leaf area) s −1 ] dose–response analyses. Structural equation modelling revealed that changes in the composition of the microbial community were attributable to changes in soil pH but unrelated to plant characteristics. Overall, these findings indicated that increased O 3 levels can induce soil alkalinisation and thereby influence soil microbial communities such that soil pH is a reliable predictor of O 3 pollution‐related changes in these communities. Highlights Elevated O 3 exhibited an overall negative influence on microorganisms. AOT40‐, POD 1 ‐ and POD 7 ‐based dose–responses performed equally well. Soil pH is a reliable predictor of O 3 pollution‐related changes in microbial communities. N addition failed to affect O 3 effects on soil microbial community.
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Claims 7
Claim · model-written summary
Higher ozone exposure was linked to significant decreases in bacteria, fungi and arbuscular mycorrhizal fungi in the poplar rhizosphere.
- Treatment
- higher levels of O 3e0
- Outcome
- bacteria, fungi, arbuscular mycorrhizal fungie0
- Direction
- decreasese0
PopulusNot reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“exposure to higher levels of O 3 was linked to significant decreases in bacteria, fungi, arbuscular mycorrhizal fungi”
t0“poplar rhizosphere soil microbial community”
Claim · model-written summary
Higher ozone exposure reduced the fungi-to-bacteria ratio.
Not reportedTreatmentComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a reduction in the ratio of fungi‐to‐bacteria”
t0“poplar rhizosphere soil microbial community”
Claim · model-written summary
Soil N addition had no impact on the soil microbial parameters.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“whereas soil N addition had no impact on these parameters”
t0“poplar rhizosphere soil microbial community”
Claim · model-written summary
No interactive effects between ozone and N were observed on soil microbial community composition.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“No interactive effects between O 3 and N were observed in the context of alterations in soil microbial community composition”
t0“poplar rhizosphere soil microbial community”
Claim · model-written summary
Concentration-based and flux-based ozone dose-response analyses performed equivalently.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“equivalent performance was observed for concentration‐based (AOT40, cumulative exposure to hourly O 3 concentrations >40 ppb) and flux‐based”
t0“poplar rhizosphere soil microbial community”
Claim · model-written summary
Structural equation modelling indicated that changes in microbial community composition were attributable to changes in soil pH but unrelated to plant characteristics.
- Outcome
- composition of the microbial communitye0
- Qualifier
- attributable to changes in soil pH but unrelated to plant characteristicse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“changes in the composition of the microbial community were attributable to changes in soil pH but unrelated to plant characteristics”
t0“poplar rhizosphere soil microbial community”
Claim · model-written summary
Increased ozone levels can induce soil alkalinisation, thereby influencing soil microbial communities.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“increased O 3 levels can induce soil alkalinisation”
t0“poplar rhizosphere soil microbial community”