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A non‐steady state model based on dual nitrogen and oxygen isotopes to constrain moss nitrate uptake and reduction

Citation

Liu, Xue-Yan et al. (2020), A non‐steady state model based on dual nitrogen and oxygen isotopes to constrain moss nitrate uptake and reduction, Dryad, Dataset, https://doi.org/10.5061/dryad.gxd2547g6

Abstract

Epilithic mosses are early colonizers of the terrestrial biosphere, constitute a special ecosystem regulating rock-atmosphere interactions, and may be more restricted in their nitrogen (N) supply than other mosses. Terrestrial mosses can take up nitrate (NO3-), a major form of bioavailable N, from soil substrates. However, the importance of substrate NO3- relative to atmospheric NO3- remains unclear in moss NO3- utilization. This has prevented the understanding of moss NO3- dynamics and its responses to environmental N loadings. Here we investigated the monthly concentrations, δ15N, and δ18O of NO3- in four epilithic moss species from August, 2006 to August, 2007 in Guiyang, southwestern China. We developed a non-steady state isotope mass-balance model based on dual N and O isotopes to evaluate fractional contributions of atmospheric NO3- (Фatm) and soil NO3- (Фsoil), moss NO3- uptake flux (Finflux), moss NO3- reduction flux (Freduction), and the percentage of NO3- reduction in total NO3- uptake of mosses (expressed as freduced). Monthly Фsoil values averaged 53 ± 13% and monthly freduced values averaged 50 ± 35%. Both monthly Freduction and freduced values increased with monthly Finflux values, particularly when Фsoil values were higher than Фatm values. However, the amount of annual NO3- reduction (219.7 ± 30.5 μg-N/g, dw) accounted for only 1.0 ± 0.2% in bulk N of mosses. We conclude that half of NO3- in epilithic mosses is derived from soil NO3- and that NO3- uptake from soil induces moss NO3- reduction, but the total NO3- assimilation contributed a low fraction to total N of study mosses. These findings are important for understanding N sources and dynamics in terrestrial mosses.

Funding

National Natural Science Foundation of China, Award: 41730855

National Natural Science Foundation of China, Award: 41273026

National Natural Science Foundation of China, Award: 41522301