Enhanced foliar 15N enrichment with increasing nitrogen addition rates: Role of plant species and nitrogen compounds

• Published in: Global change biology Vol. 29; no. 6; pp. 1591 - 1605
• Main Authors: Wang, Yinliu, Niu, Guoxiang, Wang, Ruzhen, Rousk, Kathrin, Li, Ang, Hasi, Muqier, Wang, Changhui, Xue, Jianguo, Yang, Guojiao, Lü, Xiaotao, Jiang, Yong, Han, Xingguo, Huang, Jianhui
• Format: Journal Article
• Language: English
• Published: Oxford Blackwell Publishing Ltd 01-03-2023
• Subjects: Acidification; Ammonium nitrate; arbuscular mycorrhiza; Arbuscular mycorrhizas; Carex duriuscula; Deposition; Flowers & plants; foliar N concentration; Fungi; Genetic transformation; inorganic N; N compounds; N deposition; Nitrogen; Nitrogen compounds; Nitrogen isotopes; N fixation; Plant growth; Plant species; Plants; Signatures; Steppes; Urea; δ15N
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.16555

Determining the abundance of N isotope (δ15N) in natural environments is a simple but powerful method for providing integrated information on the N cycling dynamics and status in an ecosystem under exogenous N inputs. However, whether the input of different N compounds could differently impact plant growth and their 15N signatures remains unclear. Here, the response of 15N signatures and growth of three dominant plants (Leymus chinensis, Carex duriuscula, and Thermopsis lanceolata) to the addition of three N compounds (NH4HCO3, urea, and NH4NO3) at multiple N addition rates were assessed in a meadow steppe in Inner Mongolia. The three plants showed different initial foliar δ15N values because of differences in their N acquisition strategies. Particularly, T. lanceolata (N2‐fixing species) showed significantly lower 15N signatures than L. chinensis (associated with arbuscular mycorrhizal fungi [AMF]) and C. duriuscula (associated with AMF). Moreover, the foliar δ15N of all three species increased with increasing N addition rates, with a sharp increase above an N addition rate of ~10 g N m−2 year−1. Foliar δ15N values were significantly higher when NH4HCO3 and urea were added than when NH4NO3 was added, suggesting that adding weakly acidifying N compounds could result in a more open N cycle. Overall, our results imply that assessing the N transformation processes in the context of increasing global N deposition necessitates the consideration of N deposition rates, forms of the deposited N compounds, and N utilization strategies of the co‐existing plant species in the ecosystem.
We explored the response of foliar 15N signatures of three dominant plants to the N addition of different compounds and rates based on a field work in a meadow steppe. The foliar δ15N of the three species increased with increasing N addition rates, but differences in δ15N among plant species did not converge after N addition mainly because of their ability to access different N forms. Moreover, foliar δ15N values were significantly higher with addition of NH4HCO3 and urea than NH4NO3, suggesting adding weakly acidifying N compounds could result in a more open N cycle.