A Non‐steady State Model Based on Dual Nitrogen and Oxygen Isotopes to Constrain Moss Nitrate Uptake and Reduction,Journal of Geophysical Research: Biogeosciences

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A Non‐steady State Model Based on Dual Nitrogen and Oxygen Isotopes to Constrain Moss Nitrate Uptake and Reduction
Journal of Geophysical Research: Biogeosciences ( IF 3.7 ) Pub Date : 2020-03-19 , DOI: 10.1029/2019jg005498
Xue‐Yan Liu _{1,

2,

3} , Di Wu ₁ , Xin Song ₄ , Yu‐Ping Dong ₁ , Chong‐Juan Chen ₁ , Wei Song ₁ , Cong‐Qiang Liu _{1,

2} , Keisuke Koba _{3,

5}

Affiliation

Epilithic mosses are early colonizers of the terrestrial biosphere, which constitute a special ecosystem regulating rock‐atmosphere interactions. 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 their responses to environmental N loadings. This study investigated 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 to evaluate fractional contributions of atmospheric NO₃⁻ (Ф _atm) and soil NO₃⁻ (Ф _soil), moss NO₃⁻ uptake flux (F _influx), moss NO₃⁻ reduction flux (F _reduction), and the percentage of NO₃⁻ reduction in moss NO₃⁻ uptake (f _reduced). The monthly Ф _soil values averaged 53 ± 13% and the monthly f _reduced values averaged 50 ± 35%. Both the monthly F _reduction and f _reduced increased as the monthly F _influx increased, particularly when the Ф _soil values were higher than Ф _atm values. However, the amount of annual NO₃⁻ reduction (219.7 ± 30.5 μg‐N/g, dw) accounted for only 1.0 ± 0.2% of the bulk N of the mosses. We conclude that half of the NO₃⁻ in epilithic mosses is derived from the soil NO₃⁻ and that NO₃⁻ uptake from the soil induces moss NO₃⁻ reduction, but the total NO₃⁻ assimilation contributed a low fraction of the total N in the studied mosses. These findings are important for understanding N sources and N dynamics in terrestrial mosses.

更新日期：2020-03-19

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