Uptake of various nitrogen forms by co-existing plant species in temperate and cold-temperate forests in northeast China

[Display omitted] •Co-existing forest plant species take up different forms of soil nitrogen.•Plant species show plasticity in the uptake preference of soil nitrogen form.•Canopy trees take up more glycine-derived soil nitrogen than understory.•Understory take up more soil inorganic nitrogen than canopy trees. The uptake of different soil nitrogen (N) forms by co-existing plant species is ecologically crucial, but in situ studies conducted to investigate this phenomenon across forest ecosystems are still limited. Here, stable isotope tracer techniques (13C and 15N) were used in the field, examining the uptake of inorganic and organic N by co-existing plant species, plasticity in N preference, and difference in the N uptake between layers of forest in temperate and cold-temperate forests in northeast China. Amino acid-N composed an important part (29% avg.) in the pool of available soil N (inorganic N and amino acid-N). The vegetation could take up glycine-derived N (intact uptake from 48% to 99%). With variation in habitat, Betula platyphylla and Sphagnum palustre modified their competitive abilities for uptake of intact glycine and apparent N preferences, illustrating the plasticity in the N preferences of plants. Due to the plasticity, the co-existing species appeared to show various N preference strategies in these forests. Canopy trees took up more glycine-derived N than understory plants, and vice versa for the inorganic N, which may be related to differences in the intensity of photosynthesis. This study indicates that soil amino acids are a potentially important N source, and various choices for N nutrition may alleviate inter-species competition and contribute to species co-existence in forest ecosystems in northeast China. Plasticity in N preference could underlie N source partitioning among the co-existing species. With ongoing N deposition in these and many other forest ecosystems, this research helps to clarify how soil–plant N cycling varies between canopy layers and the feedbacks that are taking place.