Abstract
In long‐lived N‐fixing plants, environmental conditions affecting plant growth and N demand vary at multiple temporal and spatial scales, and symbiont assemblages on a given host and patterns of allocation to nodule activities have been shown to vary according to environmental factors, suggesting that hosts may alter partner choice and manipulate symbiont assemblages based on shifting plant needs. This study assessed economic trade‐offs among N‐fixing symbionts of thin‐leaf alder ( Alnus tenuifolia ) by examining whether alder– Frankia associations change in response to the up‐regulation (P fertilization) and down‐regulation (N‐fertilization) of N‐fixation activities, and whether these changes are associated with differences among Frankia partners in their relative C cost and/or N benefit to A. tenuifolia . Relative to control plots, alder in +P plots had significantly higher nodule biomass and N‐fixation rates; these parameters were significantly lower in +N plots, translating to stand‐level N inputs that were more than an order of magnitude greater in +P than +N plots. Nodule respiration and N‐fixation rates were positively correlated, and analyses revealed that alder employs mechanisms to increase the efficiency of C use when N fixation is up‐regulated. Of the eight Frankia OTUs (operational taxonomic units) identified, two were dominant, with significant differences in Frankia OTU composition across samples being explained by fertilization treatment. Dominant OTUs had similar up‐ and down‐regulatory responses to treatments but differed in C costs of N fixation, while the most abundant sub‐dominant failed to up‐regulate N‐fixation rates in +P plots. Differences among Frankia OTUs in traits relevant to plant performance may form the basis for host choice and explain successional shifts in alder– Frankia assemblages. We suggest that manipulation of Frankia assemblages is an adaptation for a species such as A. tenuifolia that maintains a high dependence on atmospheric N across radically different growth environments. Because of the strong effects of thin‐leaf alder on soil N contents, it appears that host changes in C partitioning to nodule activities, including the physiological consequences of host specificity for Frankia assemblages, results in alder both driving and responding to environmental heterogeneity at small to large spatial scales.
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Claims 15
Claim · model-written summary
P fertilization increased alder nodule biomass relative to controls.
AlnusOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Relative to control plots, alder in +P plots had significantly higher nodule biomass and N‐fixation rates”
Claim · model-written summary
P fertilization increased alder N-fixation rates relative to controls.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Relative to control plots, alder in +P plots had significantly higher nodule biomass and N‐fixation rates”
Claim · model-written summary
N fertilization lowered alder nodule biomass relative to controls.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“these parameters were significantly lower in +N plots”
e1“Relative to control plots, alder in +P plots had significantly higher nodule biomass and N‐fixation rates”
Claim · model-written summary
N fertilization lowered alder N-fixation rates relative to controls.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“these parameters were significantly lower in +N plots”
e1“Relative to control plots, alder in +P plots had significantly higher nodule biomass and N‐fixation rates”
Claim · model-written summary
Stand-level N inputs in +P plots exceeded +N plots by more than an order of magnitude.
- Treatment
- +Pe0
- Outcome
- stand‐level N inputse0
- Direction
- greatere0
- Value
- more than an order of magnitudee0
- Comparator
- +N plotse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“stand‐level N inputs that were more than an order of magnitude greater in +P than +N plots”
e1“alder in +P plots”
Claim · model-written summary
Nodule respiration and N-fixation rates were positively correlated in alder.
Verbatim
e0“Nodule respiration and N‐fixation rates were positively correlated”
e1“thin‐leaf alder ( Alnus tenuifolia )”
Claim · model-written summary
Alder increased carbon use efficiency when N fixation was up-regulated.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“alder employs mechanisms to increase the efficiency of C use when N fixation is up‐regulated”
Claim · model-written summary
Two of eight identified Frankia OTUs were dominant.
FrankiaNot reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Of the eight Frankia OTUs (operational taxonomic units) identified, two were dominant”
e1“thin‐leaf alder ( Alnus tenuifolia )”
Claim · model-written summary
Fertilization explained significant differences in Frankia OTU composition.
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“significant differences in Frankia OTU composition across samples being explained by fertilization treatment”
e1“thin‐leaf alder ( Alnus tenuifolia )”
Claim · model-written summary
Dominant Frankia OTUs responded similarly to up- and down-regulation treatments.
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Dominant OTUs had similar up‐ and down‐regulatory responses to treatments”
e1“Of the eight Frankia OTUs”
e2“thin‐leaf alder ( Alnus tenuifolia )”
Claim · model-written summary
Dominant Frankia OTUs differed in carbon costs of N fixation.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Dominant OTUs had similar up‐ and down‐regulatory responses to treatments but differed in C costs of N fixation”
e1“Of the eight Frankia OTUs”
e2“thin‐leaf alder ( Alnus tenuifolia )”
Claim · model-written summary
The most abundant subdominant Frankia OTU failed to increase N fixation in +P plots.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the most abundant sub‐dominant failed to up‐regulate N‐fixation rates in +P plots”
e1“Of the eight Frankia OTUs”
e2“thin‐leaf alder ( Alnus tenuifolia )”
Claim · model-written summary
Differences in Frankia traits may explain alder host choice and successional shifts.
- Outcome
- host choice and explain successional shiftse0
- Qualifier
- Differences among Frankia OTUs in traits relevant to plant performancee0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Differences among Frankia OTUs in traits relevant to plant performance may form the basis for host choice and explain successional shifts in alder– Frankia assemblages”
Claim · model-written summary
Manipulating Frankia assemblages was suggested as an alder adaptation across different environments.
- Taxon
- A. tenuifolia
Alnus incana subsp. tenuifoliae0 - Outcome
- adaptatione0
- Qualifier
- high dependence on atmospheric Ne0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“manipulation of Frankia assemblages is an adaptation for a species such as A. tenuifolia that maintains a high dependence on atmospheric N across radically different growth environments”
Claim · model-written summary
Alder changes in carbon allocation to nodules appear to drive and respond to environmental heterogeneity.
- Organ / stage
- nodulee0
- Outcome
- driving and responding to environmental heterogeneitye0
- Qualifier
- host changes in C partitioning to nodule activitiese0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“host changes in C partitioning to nodule activities, including the physiological consequences of host specificity for Frankia assemblages, results in alder both driving and responding to environmental heterogeneity at small to large spatial scales”