Nitrogen and Carbon Isotopic Dynamics of Subarctic Soils and Plants in Southern Yukon Territory and its Implications for Paleoecological and Paleodietary Studies

Authors

Farnoush Tahmesabi, The University of Western Ontario
Fred J. Longstaffe, The University of Western OntarioFollow
Grant Zazula, Government of Yukon
Bruce Bennett, Government of Yukon

Document Type

Article

Publication Date

8-16-2017

Volume

12

Issue

8

Journal

PLOS ONE

First Page

1

URL with Digital Object Identifier

https://doi.org/10.1371/ journal.pone.0183016

Last Page

26

Abstract

We examine here the carbon and nitrogen isotopic compositions of bulk soils (8 topsoil and 7 subsoils, including two soil profiles) and five different plant parts of 79 C₃ plants from two main functional groups: herbs and shrubs/subshrubs, from 18 different locations in grasslands of southern Yukon Territory, Canada (eastern shoreline of Kluane Lake and Whitehorse area). The Kluane Lake region in particular has been identified previously as an analogue for Late Pleistocene eastern Beringia. All topsoils have higher average total nitrogen δ¹⁵N and organic carbon δ¹³C than plants from the same sites with a positive shift occurring with depth in two soil profiles analyzed. All plants analyzed have an average whole plant δ¹³C of −27.5 ± 1.2 ‰ and foliar δ¹³C of ±28.0 ± 1.3 ‰, and average whole plant δ¹⁵N of −0.3 ± 2.2 ‰ and foliar δ¹⁵N of ±0.6 ± 2.7 ‰. Plants analyzed here showed relatively smaller variability in δ¹³C than δ¹⁵N. Their average δ¹³C after suitable corrections for the Suess effect should be suitable as baseline for interpreting diets of Late Pleistocene herbivores that lived in eastern Beringia. Water availability, nitrogen availability, spacial differences and intra-plant variability are important controls on δ¹⁵N of herbaceous plants in the study area. The wider range of δ¹⁵N, the more numerous factors that affect nitrogen isotopic composition and their likely differences in the past, however, limit use of the modern N isotopic baseline for vegetation in paleodietary models for such ecosystems. That said, the positive correlation between foliar δ¹⁵N and N content shown for the modern plants could support use of plant δ¹⁵N as an index for plant N content and therefore forage quality. The modern N isotopic baseline cannot be applied directly to the past, but it is prerequisite to future efforts to detect shifts in N cycling and forage quality since the Late Pleistocene through comparison with fossil plants from the same region.