Abstract
Increases in the availability of nitrogen (N) may have consequences for plant growth and nutrient cycling in N-limited tundra plant communities. We investigated the impact alder (Alnus viridis spp. fruticosa), an N-fixing deciduous shrub, has on tundra N cycling at a hillslope located on Alaska’s Seward Peninsula. We quantified N fixation using15N2 incubations within two distinct alder communities at this site: alder shrublands located on well-drained, rocky outcroppings in the uplands and alder savannas located in water tracks along the moist toeslope of the hill. Annual N fixation rates in alder shrublands were 1.95 ± 0.68 g N m-2 year-1, leading to elevated N levels in adjacent soils and plants. Alder savannas had lower N fixation rates (0.53 ± 0.19 g N m-2 year-1), perhaps due to low phosphorus availability and poor drainage in these highly organic soil profiles underlain by permafrost. In addition to supporting higher rates of N fixation, tall-statured alder shrublands had different foliar traits than relatively short-statured alder in savannas, providing an opportunity to link N fixation to remotely-sensed variables. We were able to generate a map of the alder shrubland distribution at this site using a multi-sensor fusion approach. The change in alder shrubland distribution through time was also determined from historic aerial and satellite imagery. Analysis of historic imagery showed that the area of alder shrublands at this site has increased by 40% from 1956 to 2014. We estimate this increase in alder shrublands was associated with a 22% increase in N fixation. Our results suggest that expansion of alder shrublands has the potential to substantially alter N cycling, increase plant productivity, and redistribute C storage in upland tundra regions. An improved understanding of the consequences of N fixation within N-limited tundra plant communities will therefore be crucial for predicting the biogeochemistry of these warming ecosystems.
| Original language | English |
|---|---|
| Article number | 1099 |
| Journal | Frontiers in Plant Science |
| Volume | 10 |
| DOIs | |
| State | Published - 2019 |
Funding
We would like to thank Mary’s Igloo Native Corporation for allowing us to perform this research on their land and giving us the opportunity to share this research with their community. We would like acknowledge Rich Norby, Joanne Childs, Deanne Brice, Holly Vander Stel, Sarah Bellaire, David McLennan, Terri Velliquette, Fengming Yuan, Santosh Panda, Abbygail Ochs, Rita Keil, Bob Busey, and Breann Spencer for their help during lab work, field campaigns, and manuscript preparation. Comments from two reviewers improved this manuscript measurably. The NGEE Arctic project is supported by the Office of Biological and Environmental Research in the US Department of Energy’s Office of Science. This manuscript has been authored (in part) by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/ doe-public-access-plan).
| Funders | Funder number |
|---|---|
| Office of Biological and Environmental Research in the US Department of Energy | |
| U.S. Department of Energy | |
| Office of Science | |
| UT-Battelle | DE-AC05-00OR22725 |
Keywords
- Alnus (alder)
- Arctic
- Nitrogen cycling
- Nitrogen fixation
- Nutrient limitation
- Shrub encroachment
- Tundra
- Tundra greening