Fig 1.
Location of study areas and sampling sites in Yukon Territory, Canada.
The study area is located in the eastern part of Beringia (blue dash lines on the inset of Canada, Alaska and easternmost Asia).
Table 1.
Climate data for Kluane Lake and Whitehorse study areas.
Fig 2.
Soil profiles at Kluane Lake and their corresponding depth profiles for δ13COC, OC and δ15NTN.
(a) profile S13-6, and (b) profile S13-8. In both, data points provide average values for bulk analysis of each soil interval (indicated by the vertical lines).The reddish-brown layer is called the “Slims soil”, and separates Neoglacial loess deposits from underlying Late Pleistocene/early Holocene deposits (photographic credit: Tessa Plint).
Table 2.
Environmental data for sampling sites and number of soils and plants sampled.
Table 3.
Isotopic compositions of soil TN and OC.
Fig 3.
Mean (± SD) δ13C and δ15N of all plant parts analyzed, including fine root, root crown, leaf, stem and inflorescence.
Below-ground plant parts have higher mean δ15N than above-ground parts, and foliar δ13C is lower than that of fine roots, stems and inflorescences, but only the latter is statistically significant (see text for details).
Fig 4.
Foliar carbon and nitrogen isotopic compositions of all plant samples.
There is a weak, positive correlation between δ13C and δ15N (see text).
Table 4.
ANOVA post-hoc tests (Dunnett’s T3) results for δ13C differences among plant tissues.
Table 5.
ANOVA post-hoc tests (Tukey’s HSD) for foliar isotopic differences between sites (plants sampled ≥5).
Fig 5.
Average N and C contents of plant parts according to sampling year.
In both 2012 and 2013, root crowns have the highest N content whereas stems have the lowest (see text); likewise, during both years, carbon contents are highest in stems, and lowest in leaves.
Table 6.
ANOVA post-hoc tests (Dunnett’s T3) for differences in C and N contents between different plant parts.
Fig 6.
(a) Areal view of the Slims River delta; (b) Slims River vegetation in August.
(photographic credits: Fred Longstaffe and Tessa Plint).
Fig 7.
Comparison of topsoil and foliar average (± SD) C and N isotopic compositions.
Smaller site-to-site variations in topsoil δ15NTN relative to foliar δ15N likely reflect a combination of soil processes and plant sample size and species (see text).
Fig 8.
Nitrogen versus carbon isotopic compositions of fine root, root crown, leaf, stem and inflorescence.
The wide spread in δ15N is typical of nitrogen-limited ecosystems, and utilization of a range of soil nitrogen sources (see text).
Fig 9.
A simplified model for the “openness” of the N cycle in ecosystems with high (9a) and low (9b) N availability.
(9a): (a) N mineralization: Conversion of organic N to NH4+ (ε = 0–5 ‰); (b) Microbial assimilation: incorporation of NH4+ into microbial biomass (ε = 14–20 ‰); (c) NH3 volatilization: conversion of NH4+(aq) to NH3(g) (ε = 40–60 ‰); (d) Nitrification: conversion of NH4+ to NO3- (ε = 15–35 ‰); (e) Plant uptake and assimilation of NH4+ (ε = 9–18 ‰); (f) Plant uptake and assimilation of NO3- (ε = 0–19 ‰); (g) NO3- leaching (ε = 0–1 ‰); (h) Denitrification: conversion of NO3- to N2O, N2 and NO2 (ε = 28–33 ‰).(9b): (a) N mineralization: Conversion of organic N to NH4+ (ε = 0–5 ‰); (b) Microbial assimilation: incorporation of NH4+ into microbial biomass (ε = 14–20 ‰); (c) Nitrification: conversion of NH4+ to NO3- (ε = 15–35 ‰); (d) Plant uptake and assimilation of NH4+ (ε = 9–18 ‰); (e) Plant uptake and assimilation of NO3- (ε = 0–19 ‰). Values of ε are from Robinson [50] and Houlton and Bai [51]).