Pitfalls and new mechanisms in moss isotope biomonitoring of atmospheric nitrogen deposition.
Moss N isotope (δ(15)N(bulk)) 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 δ(15)N(bulk). We tested this question by investigation of δ(15)N(bulk) and δ(15)NO(3)(-) in mosses under the dominance of RDN in N depositions of Guiyang, SW China. The δ(15)N(bulk) of mosses on bare rock (-7.9‰) was unable to integrate total dissolved N (TDN) (δ(15)N = -6.3‰), but it reflected δ(15)N-RDN (-7.5‰) exactly. Moreover, δ(15)N-NO(3)(-) in mosses (-1.7‰) resembled that of wet deposition (-1.9‰). These isotopic approximations, together with low isotopic enrichment with moss [NO(3)(-)] variations, suggest the inhibition of moss NRA by RDN. Moreover, isotopic mixing modeling indicated a negligible contribution from NO(3)(-) to moss δ(15)N(bulk) when the RDN/NO(3)(-) reaches 3.8, at which maximum overestimation (21%) of RDN in N deposition can be generated using moss δ(15)N(bulk) as δ(15)N-TDN. Moss δ(15)N-NO(3)(-) can indicate atmospheric NO(3)(-) under distinctly high RDN/NO(3)(-) in deposition, although moss δ(15)N(bulk) 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.
State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550002, China.
Xue-Yan
XY
Liu
Keisuke
K
Koba
Cong-Qiang
CQ
Liu
Xiao-Dong
XD
Li
Muneoki
M
Yoh
D000393:Air Pollutants / Q000032:analysis* / Q000378:metabolism; D000704:Analysis of Variance; D044002:Bryophyta / Q000737:chemistry / Q000378:metabolism*; D002681:China; D058440:Denitrification; D004784:Environmental Monitoring / Q000379:methods*; D009566:Nitrates / Q000032:analysis* / Q000378:metabolism; D009587:Nitrogen Isotopes / Q000032:analysis / Q000378:metabolism
D000393:Air Pollutants; D009566:Nitrates; D009587:Nitrogen Isotopes