Vertical Changes in the Flux of Atmospheric Nitrate From a Forest Canopy to the Surface Soil Based on Δ¹⁷O Values

Abstract

The vertical profiles of the proportion of atmospheric NO 3 − to total NO 3 − were different from those of atmospheric NO 3 − flux • The forest canopy retained a large portion of the deposited atmospheric NO 3 − • The retention rates of atmospheric NO 3 − were different among different canopy types Supporting Information:

Isotope Constraints on Nitrate Exchanges Between Precipitation and Forest Canopy

“…Accordingly, it can be concluded that the replenishment of 𝐴𝐴 p-NO3 − and 𝐴𝐴 n-NO3 − was generally higher than the loss of 𝐴𝐴 b-NO − retention, which caused higher fluxes of 𝐴𝐴 t-NO3 − than 𝐴𝐴 b-NO3 − (Figure 3b). Lower 𝐴𝐴 Δ 17 Ot-NO 3 − than the corresponding 𝐴𝐴 17 Ob-NO 3 − (by −4.5 ± 6.5‰ for broadleaved forests and −2.7 ± 1.5‰ for coniferous forests; Figure 4) verified the microbial nitrification within canopies as a significant 𝐴𝐴 NO3 − utor to 𝐴𝐴 t-NO3 − (Guerrieri et al, 2015(Guerrieri et al, , 2020Inoue et al, 2021;Shi et al, 2014). This finding was supported by the generally lower 𝐴𝐴 𝐴𝐴 18 Ot-NO 3 − and 𝐴𝐴 𝐴𝐴 15 Nt-NO 3 − signatures relative to the corresponding 𝐴𝐴 𝐴𝐴 18 Ob-NO 3 − and 𝐴𝐴 𝐴𝐴 15 Nb-NO 3 − values, respectively (Figure 4).…”

“…Ammonium ( 𝐴𝐴 NH + 4 ) in the canopy from both atmospheric deposition and mineralization of organic matter in the canopy can be a substrate of nitrification in the canopy (Guerrieri et al, 2020;Wania et al, 2002). While the genetic approaches allow measuring the abundance of nitrifying species in the phyllosphere, they cannot estimate their activity and quantify the contribution of 𝐴𝐴 n-NO3 − in canopies to 𝐴𝐴 t-NO3 − (Guerrieri et al, 2020;Inoue et al, 2021). Therefore, although canopy nitrification has been recognized as the other contributor to 𝐴𝐴 t-NO3 − , extent studies emphasized less on the exact contribution of 𝐴𝐴 n-NO3 − (Garten, 1992;Heaton et al, 1997).…”

“…Due to high emissions of both fossil and non-fossil fuel N oxides, atmospheric 𝐴𝐴 NO3 − inputs into many terrestrial ecosystems have been elevated during past decades (Liu et al, 2013;Song et al, 2021;Yu et al, 2019). The quantity and chemical composition of throughfall 𝐴𝐴 NO3 − ( 𝐴𝐴 t-NO3 − ) reflect a mixture of wet and dry deposition (Figure 1) and have been chemically or biologically modified during precipitation-canopy 𝐴𝐴 NO3 − exchanges (Garten, 1992;Heaton et al, 1997;Inoue et al, 2021), which mainly include two gains and one loss/retention processes (Figure 1). First, the filtering and accumulation of particulate 𝐴𝐴 NO3 − ( 𝐴𝐴 p-NO3 − ) in the tree canopy (Liu et al, 2013;Matsumoto et al, 2020) (Bortolazzi et al, 2021;Lindberg et al, 1986;Lovett & Lindberg, 1993) (Figure 1).…”

“…Ammonium ($${\text{NH}}_{4}^{+}$$) in the canopy from both atmospheric deposition and mineralization of organic matter in the canopy can be a substrate of nitrification in the canopy (Guerrieri et al., 2020; Wania et al., 2002). While the genetic approaches allow measuring the abundance of nitrifying species in the phyllosphere, they cannot estimate their activity and quantify the contribution of $$\mathrm{n}\mbox{-}{{\text{NO}}_{3}}^{-}$$ in canopies to $$\mathrm{t}\mbox{-}{{\text{NO}}_{3}}^{-}$$ (Guerrieri et al., 2020; Inoue et al., 2021). Therefore, although canopy nitrification has been recognized as the other contributor to $$\mathrm{t}\mbox{-}{{\text{NO}}_{3}}^{-}$$, extent studies emphasized less on the exact contribution of $$\mathrm{n}\mbox{-}{{\text{NO}}_{3}}^{-}$$ to $$\mathrm{t}\mbox{-}{{\text{NO}}_{3}}^{-}$$ than on that of $$\mathrm{p}\mbox{-}{{\text{NO}}_{3}}^{-}$$ (Garten, 1992; Heaton et al., 1997).…”

“…Due to high emissions of both fossil and non‐fossil fuel N oxides, atmospheric $${{\text{NO}}_{3}}^{-}$$ inputs into many terrestrial ecosystems have been elevated during past decades (Liu et al., 2013; Song et al., 2021; Yu et al., 2019). The quantity and chemical composition of throughfall $${{\text{NO}}_{3}}^{-}$$ ($$\mathrm{t}\mbox{-}{{\text{NO}}_{3}}^{-}$$) reflect a mixture of wet and dry deposition (Figure 1) and have been chemically or biologically modified during precipitation‐canopy $${{\text{NO}}_{3}}^{-}$$ exchanges (Garten, 1992; Heaton et al., 1997; Inoue et al., 2021), which mainly include two gains and one loss/retention processes (Figure 1).…”