Fire increases soil nitrogen retention and alters nitrogen uptake patterns among dominant shrub species in an Arctic dry heath tundra

• Published in: Science of The Total Environment
• Main Authors: Xu, Wenyi, Elberling, Bo, Ambus, Per Lennart
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2021
• Subjects: N tracing; Microbial biomass phosphorus; Shrub cutting; Tundra fire; Warming; Arctic; Greenland; Betula nana; Climate change; Tundra
• Online Access: https://curis.ku.dk/portal/da/publications/fire-increases-soil-nitrogen-retention-and-alters-nitrogen-uptake-patterns-among-dominant-shrub-species-in-an-arctic-dry-heath-tundra(ebf9f001-aedb-478c-b36e-1ab9c01b636a).html; https://doi.org/10.1016/j.scitotenv.2021.150990; https://curis.ku.dk/ws/files/289321869/1_s2.0_S004896972106068X_main.pdf

Climate change increases the frequency and severity of fire in the Arctic tundra regions. We assessed effects of fire in combination with summer warming on soil biogeochemical N- and P cycles with a focus on mineral N over two years following an experimental fire in a dry heath tundra, West Greenland. We applied stable isotopes ( 15 NH 4 + -N and 15 NO 3 − -N) to trace the post-fire mineral N pools. The partitioning of 15 N in the bulk soils, soil dissolved organic N (TDN), microbes and plants (roots and leaves) was established. The fire tended to increase microbial P pools by four-fold at both one and two years after the fire. Two years after the fire, the bulk soil 15 N recovery has decreased to 10.4% in unburned plots while relatively high recovery was maintained (30%) in burned plots, suggesting an increase in soil N retention after the fire. The contribution of microbial 15 N recovery to bulk soil 15 N recovery increased from 11.2% at 21 days to 31.5% two years after the fire, suggesting that higher post-fire N retention was due largely to the increased incorporation of N into microbial biomass. Fire also increased 15 N recovery in bulk roots after one and two years, but only under summer warming. This suggests that higher retention of post-fire N can strongly increase the potential for N uptake of recovering plants under a future warmer climate. There was significantly lower 15 N enrichment of Betula nana leaves while higher 15 N enrichment of Vaccinium uliginosum leaves (after three years) in burned than control plots. This shows that fire can alter the N uptake differently among dominant shrub species in this tundra ecosystem, and implies that wildfires may change plant species composition in the longer term.