Fate of atmospherically deposited NH₄⁺ and NO₃⁻ in two temperate forests in China: temporal pattern and redistribution

Abstract

The impacts of anthropogenic nitrogen (N) deposition on forest ecosystems depend in large part on its fate. However, our understanding of the fates of different forms of deposited N as well as the redistribution over time within different ecosystems is limited. In this study, we used the 15N‐tracer method to investigate both the short‐term (1 week to 3 months) and long‐term (1–3 yr) fates of deposited NH4+ or NO3− by following the recovery of the 15N in different ecosystem compartments in a larch plantation forest and a mixed forest located in northeastern China. The results showed similar total ecosystem retention for deposited NH4+ and NO3−, but their distribution within the ecosystems (plants vs. soil) differed distinctly particularly in the short‐term, with higher 15NO3− recoveries in plants (while lower recoveries in organic layer) than found for 15NH4+. The different short‐term fate was likely related to the higher mobility of 15NO3− than 15NH4+ in soils instead of plant uptake preferences for NO3− over NH4+. In the long‐term, differences between N forms became less prevalent but higher recoveries in trees (particularly in the larch forest) of 15NO3− than 15NH4+ tracer persisted, suggesting that incoming NO3− may contribute more to plant biomass increment and forest carbon sequestration than incoming NH4+. Differences between the two forests in recoveries were largely driven by a higher 15N recovery in the organic layer (both N forms) and in trees (for 15NO3−) in the larch forest compared to the mixed forest. This was due to a more abundant organic layer and possibly higher tree N demand in the larch forest than in the mixed forest. Leachate 15N loss was minor (<1% of the added 15N) for both N forms and in both forests. Total 15N recovery averaged 78% in the short‐term and decreased to 55% in the long‐term but with increasing amount of 15N label (re)‐redistributed into slow turn‐over pools (e.g., trees and mineral soil). The different retention dynamics of deposited NH4+ and NO3− may have implications in environmental policy related to the anthropogenic emissions of the two N forms.

Dynamics and multi‐annual fate of atmospherically deposited nitrogen in montane tropical forests

“…The 15 N tracer method is the only approach currently available to trace and quantify the fate and (re)distribution of deposited N over multiyear periods in forest ecosystems (Nadelhoffer et al, 1999; Templer et al, 2012). Many studies have examined the fate of various forms of 15 N added to forest ecosystems (Feng et al, 2008; Goodale, 2017; Gurmesa et al, 2016; Li et al, 2019; Liu, Peng, et al, 2017; Liu, Yu, et al, 2017; Templer et al, 2012; Wang et al, 2018). Most of these, largely located in temperate and boreal forests (see Templer et al, 2012), showed most added 15 N ending up in the organic soil (Feng et al, 2008; Goodale, 2017; Li et al, 2019; Liu, Peng, et al, 2017; Templer et al, 2012).…”

“…Many studies have examined the fate of various forms of 15 N added to forest ecosystems (Feng et al, 2008; Goodale, 2017; Gurmesa et al, 2016; Li et al, 2019; Liu, Peng, et al, 2017; Liu, Yu, et al, 2017; Templer et al, 2012; Wang et al, 2018). Most of these, largely located in temperate and boreal forests (see Templer et al, 2012), showed most added 15 N ending up in the organic soil (Feng et al, 2008; Goodale, 2017; Li et al, 2019; Liu, Peng, et al, 2017; Templer et al, 2012). But few temperate studies traced the distribution of deposited N for more than 2 years (Goodale, 2017; Krause et al, 2012; Li et al, 2019; Nadelhoffer et al, 2004; Preston & Mead, 1994; Wessel et al, 2013), and the three 15 N tracer studies in tropical and subtropical forests suggest instead that plants and mineral soil sinks are more important (Gurmesa et al, 2016; Liu, Yu, et al, 2017; Wang et al, 2018).…”

“…Most of these, largely located in temperate and boreal forests (see Templer et al, 2012), showed most added 15 N ending up in the organic soil (Feng et al, 2008; Goodale, 2017; Li et al, 2019; Liu, Peng, et al, 2017; Templer et al, 2012). But few temperate studies traced the distribution of deposited N for more than 2 years (Goodale, 2017; Krause et al, 2012; Li et al, 2019; Nadelhoffer et al, 2004; Preston & Mead, 1994; Wessel et al, 2013), and the three 15 N tracer studies in tropical and subtropical forests suggest instead that plants and mineral soil sinks are more important (Gurmesa et al, 2016; Liu, Yu, et al, 2017; Wang et al, 2018). The long‐term retention dynamics of deposited N remains especially uncertain as N initially retained in the organic soil and mineral soil may redistribute to woody plants (Goodale, 2017) or be lost from the ecosystem altogether (Preston & Mead, 1994; Wessel et al, 2013).…”

“…Previous short‐term 15 N tracer studies have suggested that deposited and may have different fates since is preferred for uptake by soil microbes or immobilized in mineral soil while is more prone to leaching and gaseous loss (Jacob & Leuschner, 2015; Liu, Peng, et al, 2017; Providoli et al, 2006; Wang et al, 2018). However, most long‐term 15 N tracer studies focused on or separately or did not differentiate (Goodale, 2017; Gurmesa et al, 2016; Providoli et al, 2005; Wessel et al, 2013); thus, the different fates of deposited and were seldom compared for the same forests over multiple years (Li et al, 2019; Nadelhoffer et al, 2004; Preston et al, 1990; Preston & Mead, 1994). Furthermore, while we may expect differences in the patterns of N retention in forests with different successional status due to different species composition and N status (Li et al, 2019), few studies have compared different forests in a given site (Li et al, 2019; Nadelhoffer et al, 2004).…”

“…However, most long‐term 15 N tracer studies focused on or separately or did not differentiate (Goodale, 2017; Gurmesa et al, 2016; Providoli et al, 2005; Wessel et al, 2013); thus, the different fates of deposited and were seldom compared for the same forests over multiple years (Li et al, 2019; Nadelhoffer et al, 2004; Preston et al, 1990; Preston & Mead, 1994). Furthermore, while we may expect differences in the patterns of N retention in forests with different successional status due to different species composition and N status (Li et al, 2019), few studies have compared different forests in a given site (Li et al, 2019; Nadelhoffer et al, 2004).…”