Controls on Fine-Scale Spatial and Temporal Variability of Plant-Available Inorganic Nitrogen in a Polygonal Tundra Landscape.
Norby, R. J., Sloan, V. L., Iversen, C. M., & Childs, J. . 2018.
Abstract
Nitrogen availability in the Arctic strongly influences plant productivity and distribution, and in
permafrost systems with patterned ground,
ecosystem carbon and nutrient cycling can vary
substantially over short distances. Improved
understanding of fine-scale spatial and temporal
variation in soil N availability is needed to better
predict tundra responses to a warming climate. We
quantified plant-available inorganic nitrogen at
multiple soil depths in 12 microhabitats associated
with a gradient from low-center ice-wedge polygons to high-center polygons in coastal tundra at
Utqia_gvik (formerly Barrow), Alaska. We measured
vegetation composition, biomass, N content, and
rooting depth distribution, as well as soil temperature, moisture, pH, and thaw depth to determine
relationships between the spatial and temporal
variability in N availability and environmental and
vegetation drivers. Soil moisture varied across the
microhabitats of the polygonal terrain and was the
most important variable linked to distribution of
both ammonium and nitrate, with ammonium
predominating in wetter areas and nitrate pre-
dominating in drier areas. Total inorganic N avail-
ability increased as the soil in the active layer
thawed, but the newly available N near the permafrost boundary late in the season was apparently
not available to roots and did not contribute to
plant N content. Nitrate in the drier sites also was
not associated with plant N content, raising the
possibility of N losses from this N-limited ecosystem. The strong relationship between soil moisture,
inorganic N availability, and plant N content implies that understanding hydrological changes that
may occur in a warming climate is key to deter-
mining nutrient cycling responses in complex
polygonal tundra landscapes.
Key Words
Arctic; ice-wedge polygons; tundra; microhabitat; thaw; active layer; nitrate; ammo- nium; plant-available nitrogen; root distribution.
