Nitrogen and carbon isotopic dynamics of subarctic soils and plants in southern Yukon Territory and its implications for paleoecological and paleodietary studies.

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 ?15N and organic carbon ?13C 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 ?13C of -27.5 ± 1.2 ‰ and foliar ?13C of -28.0 ± 1.3 ‰, and average whole plant ?15N of -0.3 ± 2.2 ‰ and foliar ?15N of -0.6 ± 2.7 ‰. Plants analyzed here showed relatively smaller variability in ?13C than ?15N. Their average ?13C 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 ?15N of herbaceous plants in the study area. The wider range of ?15N, 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 ?15N and N content shown for the modern plants could support use of plant ?15N 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.

SUBMITTER: Tahmasebi F 

PROVIDER: S-EPMC5559067 | biostudies-literature | 2017

REPOSITORIES: biostudies-literature