Spruce trees absorb intact urea from soils on permafrost ...

• Main Author: Fujii, Kazumichi
• Format: Dataset
• Language: English
• Published: Dryad 2021
• Subjects: Canada; Inuvik; Northwest Territories; Active layer thickness; Ice; permafrost; Subarctic; Tundra; wedge*
• Online Access: https://dx.doi.org/10.5061/dryad.msbcc2fz0; https://datadryad.org/stash/dataset/doi:10.5061/dryad.msbcc2fz0

Biomass productivity of black spruce trees is strongly limited by soil nitrogen in shallow active layer on permafrost. Trees and mycorrhizal roots are known to absorb amino acids to bypass slow nitrogen mineralization in nitrogen-limited boreal forest soils. However, the amino acid uptake strategy of tree roots cannot fully explain their advantages in the competition for soil nitrogen with other plants and microbes. Here, we provide evidence that some spruce tree roots absorb intact urea. Tree roots develop plasticity to utilize different nitrogen sources, depending on active layer thickness. Urea uptake is limited to soils with shallow permafrost, where urea accumulates due to limited microbial mineralization activity. This contrasts with soils with deep permafrost, where tree roots absorb amino acids and inorganic nitrogen. Allocation of photosynthate to fine roots in colder subsoil above shallow permafrost provides advantages for trees monopolizing urea-nitrogen. Despite lower energy efficiency of urea ... : 1. Field site We compared forest tundra sites dominated by black spruce (Picea mariana L.) on clayey soils and sandy soils near Inuvik, Northwest Territories, Canada (N68°03’, W133°30’). Inuvik has a subarctic climate; the mean annual air temperature is –8.8 ºC. The soil surface consists of lichen (Cladonia mitis L. and Cladonia stellaris L.)-covered mounds and moss (Pleurozium schreberi L., Hylocomium splendens L., and Sphagnum fuscum L.)-covered depressions. The wide variation in permafrost table depth was caused by the differences in geological substrates (glaciofluvial sands and fine-grained sediments) (Tarnocai et al., 1993; Fujii et al., 2019). Clayey soils are derived from a mixture of fine-grained sediments (27–37 % clay and 22–30 % sand), while sandy soils are derived from glaciofluvial sands (8–12 % clay and 73–75 % sand). The clayey soil is classified as Glacic Aquorthel due to the presence of ice wedge and redox morphological feature within the profile, whereas the sandy soil is classified as ...