Alder Distribution and Expansion Across a Tundra Hillslope: Implications for Local N Cycling

Frontiers in Plant Science

Mark J. Lara¹  Peter E. Thornton³  Jitendra Kumar³  Stan D. Wullschleger³  Verity G. Salmon³  Colleen M. Iversen³  Amy L. Breen⁴ 

[1] Department of Geography, University of Illinois, Urbana, IL, United States;Department of Plant Biology, University of Illinois, Urbana, IL, United States;Environmental Sciences Division and Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, TN, United States;International Arctic Research Center, University of Alaska, Fairbanks, AK, United States;

关键词: Alnus (alder);    arctic;    nitrogen cycling;    nitrogen fixation;    shrub encroachment;    tundra;   

DOI  :  10.3389/fpls.2019.01099

来源: DOAJ

【 摘 要 】

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 using 15N2 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.

【 授权许可】

Unknown