Pitfalls and New Mechanisms in Moss Isotope Biomonitoring of Atmospheric Nitrogen Deposition

• Published in: Environmental science & technology Vol. 46; no. 22; pp. 12557 - 12566
• Main Authors: Liu, Xue-Yan, Koba, Keisuke, Liu, Cong-Qiang, Li, Xiao-Dong, Yoh, Muneoki
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 20.11.2012
• Subjects: Air Pollutants - analysis; Air Pollutants - metabolism; Analysis methods; Analysis of Variance; Applied sciences; Approximation; Atmospheric pollution; Bryophyta - chemistry; Bryophyta - metabolism; China; Denitrification; Environmental monitoring; Environmental Monitoring - methods; Exact sciences and technology; Isotopes; Mosses; Nitrates; Nitrates - analysis; Nitrates - metabolism; Nitrogen; Nitrogen Isotopes - analysis; Nitrogen Isotopes - metabolism; Pollution; Sedimentation & deposition; Asia; China; Guiyang China; Isotopic analysis; Musci; Atmospheric fallout; Nitrogen 15; Enzyme; Nitrogen compounds; Bryophyta; Biological indicator; Biological monitoring; Enzymatic activity; Nitrate reductase; Stable isotopes; Air pollution; Oxidoreductases
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es300779h

Moss N isotope (δ15Nbulk) has been used to monitor N deposition, but it remains questionable whether inhibition of nitrate reductase activity (NRA) by reduced dissolved N (RDN) engenders overestimation of RDN in deposition when using moss δ15Nbulk. We tested this question by investigation of δ15Nbulk and δ15NO3 – in mosses under the dominance of RDN in N depositions of Guiyang, SW China. The δ15Nbulk of mosses on bare rock (−7.9‰) was unable to integrate total dissolved N (TDN) (δ15N = −6.3‰), but it reflected δ15N-RDN (−7.5‰) exactly. Moreover, δ15N-NO3 – in mosses (−1.7‰) resembled that of wet deposition (−1.9‰). These isotopic approximations, together with low isotopic enrichment with moss [NO3 –] variations, suggest the inhibition of moss NRA by RDN. Moreover, isotopic mixing modeling indicated a negligible contribution from NO3 – to moss δ15Nbulk when the RDN/NO3 – reaches 3.8, at which maximum overestimation (21%) of RDN in N deposition can be generated using moss δ15Nbulk as δ15N-TDN. Moss δ15N-NO3 – can indicate atmospheric NO3 – under distinctly high RDN/NO3 – in deposition, although moss δ15Nbulk can reflect only the RDN therein. These results reveal pitfalls and new mechanisms associated with moss isotope monitoring of N deposition and underscore the importance of biotic N dynamics in biomonitoring studies.