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

Xulun Zhou,Yinghua Li,Feifei Zhu,Xueyan Wang,Ang Wang,Erik A Hobbie,Yunting Fang

doi:10.1186/s13717-021-00306-4

Abstract

BackgroundConifers 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 15N 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. NH4+ vs. NO3−) to total N uptake, based on 15N natural abundance of plant and soil available N, in four mature conifers (Pinus koraiensis, Pinus sylvestris, Picea koraiensis, and Larix olgensis).ResultsDON 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.ConclusionsOur 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.

Highlights

Conifers partition different N forms from soil, including ammonium, nitrate, and dissolved organic N (DON), to sustain plant growth
Results from such work may not represent the uptake patterns of DON by mature conifers because these amino acids generally only account for a small fraction of organic N pools (Yu et al 2002; Andersson and Berggren 2005)
There were no significant differences in the Natural abundance of 15N (δ15N) of soil ammonium and nitrate among the four plantations (P > 0.05), with ammonium from 2.5 to 5.8‰ and nitrate from −0.7 to 3.9‰ (Fig. 3)

Summary

Introduction

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 15N labelling, but knowledge of the contribution of DON to mature conifers’ N uptake is still scarce. Conifers use different N forms from soil as their primary N sources, including ammonium, nitrate, and dissolved organic N (DON) (Näsholm et al 2009; Orwin et al 2011). Previous experiments have studied the contribution of specific amino acid forms using 15N- and 13C-labelled glycine, arginine, or glutamine (Öhlund and Näsholm 2004; Persson et al 2006; Zhu et al 2019). DON is widely accepted as a potentially important N source (Näsholm et al 2009; Andersen et al 2017), the knowledge of the contribution of DON to N uptake by mature conifers is still limited

Methods

Results

Discussion

Conclusion