US EPA

3549123 

Journal Article 

Effects of permafrost thaw on nitrogen availability and plant-soil interactions in a boreal Alaskan lowland 

Finger, RA; Turetsky, MR; Kielland, K; Ruess, RW; Mack, MC; Euskirchen, ES 

2016 

Yes 

Journal of Ecology
ISSN: 0022-0477
EISSN: 1365-2745 

104 

6 

1542-1554 

10.1111/1365-2745.12639 

WOS:000385915200004 

Increasing rates of permafrost thaw in boreal peatlands are
converting conifer forests to waterlogged open wetlands. Permafrost thaw increases soil nitrogen
(N) availability, but it is unclear whether such changes are due solely to changes in surface
soil N mineralization or N mobilization from thawing permafrost soils at depth. We examined plant
species composition and N availability along triplicate permafrost thaw gradients in Alaskan
peatlands. Each gradient comprised four community types including: (i) a permafrost peatland with
intact permafrost, (ii) a drunken forest experiencing active thaw, (iii) a moat representing
initial complete thaw and (iv) a collapse scar bog representing several decades of post-thaw
succession. Concentrations of dissolved organic (DON) and inorganic N (DIN) in the upper 60cm of
soil increased along the permafrost thaw gradients. The drunken forest had the greatest mean
concentrations of total dissolved N relative to the other community types, primarily due to
greater concentrations of large molecular DON. The moat and collapse bog had significantly
greater inorganic N concentrations than the permafrost or drunken forest, suggesting that changes
in N availability are not a short-term effect, but can be sustained for decades or centuries.
Across all plant community types, DIN and DON concentrations increased with soil depth during
maximum seasonal ice thaw (September), suggesting that deeper soil horizons are important
reservoirs of N post-thaw. Vegetation responses to permafrost thaw included changes in plant
community composition shifting from upland forest species to hydrophilic vegetation with deeper
rooting profiles in the collapse scar bogs and changes in foliar N and N-15 values. N
concentrations in plant foliage and litterfall increased with concentrations of DIN during
collapse bog succession, suggesting that plants are utilizing additional mineralized N.Synthesis.
Our results suggest that the conversion of forest to wetlands associated with permafrost thaw in
boreal lowlands increases N availability, at least in part by increasing turnover of deep soil
organic matter. Plants appear to utilize these additional deeper N sources over timescales of
years to centuries following permafrost thaw. 

climate change; collapse scar bog; nutrients; peatlands; rooting depth; stable isotopes; subarctic; thermokarst; N-15