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As warming increases permafrost thaw and stimulates microbial activity, the resulting increases in nutrient availability are anticipated to alleviate plant nutrient limitations. These shifts aboveground may coincide with changes in root function below-ground, especially that of mycorrhizal degradative enzymes. This project characterized the responses of two contrasting tundra shrub species to a long-term experimental fertilization gradient. All data was collected from the US Arctic Long Term Ecological Research Network (LTER) fertilization gradient experiment established in 2006 in moist acidic tussock tundra. We measured the activity of five enzymes (leucine aminopeptidase, N-acetyl glucosaminidase, acid phosphatase, phenol oxidase, and peroxidase) on ectomycorrhizal (EcM)-colonized Betula nana roots and ericaceous Rhododendron tomentosum roots. We also characterized soil chemistry and measured stem lengths of Betula nana and Rhododendron tomentosum in the same plots.
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Nonlinear responses of ericaceous and ectomycorrhizal Arctic shrubs across a long‐term experimental nutrient gradient
Abstract In the Arctic tundra, warming is anticipated to stimulate nutrient release and potentially alleviate plant nutrient limitations. Typically simulated by fertilization experiments that saturate plant nutrient demand, future increases in soil fertility are thought to favor ectomycorrhizal (EcM) over ericaceous shrubs and have often been identified as a key driver of Arctic shrub expansion. However, the projected increases in fertility will likely vary in their alleviation of nutrient limitations. The resulting responses of shrubs and their mycorrhizae across the gradient of nutrient limitation may be nonlinear and could contradict the current predictions of tundra vegetation shifts. We compared the functional responses of two dominant shrubs, EcM dwarf birch (Betula nana) and ericaceous Labrador tea (Rhododendron tomentosum), across a long‐term nitrogen and phosphorus fertilization gradient experiment in Arctic Alaska. Using linear mixed‐effects modeling, we tested the responses of shrub cover, height, and root enzyme activities to soil fertility. We found thatB. nanacover and height linearly increased with soil fertility. In contrast,R. tomentosumcover initially increased, but decreased after surpassing the intermediate levels of increased soil fertility. Its height did not change. Enzyme activity did not respond to soil fertility on EcM‐colonizedB. nanaroots, but sharply declined onR. tomentosumroots. Overall, the nonlinear responses of shrubs to our fertility gradient demonstrate the importance of experiments grounded in replicated regression design. Our results indicate that under moderate increases in soil fertility, Arctic shrub expansion may not only include deciduous EcM shrubs but also ericaceous shrubs. Regardless of shifts aboveground, changes in root enzyme activity belowground point to some EcM shrub species playing a more influential role in tundra soils; as EcM roots remained steady in their liberation of soil organic nutrients with heightened soil fertility, degradative root enzyme activity on the dominant ericaceous shrub dropped—in some instances with even the slightest increase in fertility.
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- PAR ID:
- 10571325
- Publisher / Repository:
- ESA Journals
- Date Published:
- Journal Name:
- Ecosphere
- Volume:
- 15
- Issue:
- 7
- ISSN:
- 2150-8925
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/ecs2.4888
