Soil nitrogen pools and plant uptake at sub-zero soil temperature in a cool temperate forest soil: a field experiment using 15N labeling

Abstract

Winter biogeochemical processes have received considerable attention. Biological processes (e.g., microbial respiration and plant photosynthesis) do not cease, even at sub-zero temperatures. However, our knowledge of plant nitrogen (N) uptake at sub-zero soil temperatures is particularly limited for deciduous plant species, which do not have leaves during winter. We investigated plant N uptake by evergreen and deciduous species and soil N processes during sub-zero soil temperatures in cool temperate forest soil. Isotopically labelled nitrate (NO3-15N) was injected into soil as a tracer of plant uptake and soil N dynamics at sub-zero temperature soil at a cool temperate field site. Over a period of 41 days, 6–48 mg/kg DW−1 of 15N accumulated in evergreen species and deciduous tree species. Furthermore, the 15N content in ammonium increased, suggesting ammonium production at sub-zero soil temperatures. The increase in 15NH4 was positively correlated with soil moisture, indicating an important role for soil water in N dynamics at sub-zero soil temperatures. Our findings demonstrate that N uptake by plants and soil N transformation did not cease at sub-zero soil temperatures. Further studies are needed to understand the importance of N dynamics at sub-zero soil temperatures.