Nitrogen uptake strategies of mature conifers in Northeastern China, illustrated by the 15 N natural abundance method

Background Conifers partition different N forms from soil, including ammonium, nitrate, and dissolved organic N (DON), to sustain plant growth. Previous studies focused on inorganic N sources and specific amino acid forms using 15 N labelling, but knowledge of the contribution of DON to mature conifers’ N uptake is still scarce. Here, we quantified the contribution of different N forms (DON vs. NH 4 + vs. NO 3 − ) to total N uptake, based on 15 N natural abundance of plant and soil available N, in four mature conifers ( Pinus koraiensis , Pinus sylvestris , Picea koraiensis , and Larix olgensis ). Results DON contributed 31%, 29%, 28%, and 24% to total N uptake by Larix olgensis , Picea koraiensis , Pinus koraiensis , and Pinus sylvestris , respectively, whereas nitrate contributed 42 to 52% and ammonium contributed 19 to 29% of total N uptake for these four coniferous species. Conclusions Our results suggested that all four conifers could take up a relatively large proportion of nitrate, while DON was also an important N source for the four conifers. Given that DON was the dominant N form in study soil, such uptake pattern of conifers could be an adaptive strategy for plants to compete for the limited available N sources from soil so as to promote conifer growth and maintain species coexistence.