Inorganic nitrogen immobilization in live and sterile soil of old-growth conifer and hardwood forests: Implications for ecosystem nitrogen retention

David Bruce Lewis, Jason Philip Kaye

Research output: Contribution to journalArticle

24 Scopus citations

Abstract

Rapid immobilization of inorganic nitrogen (N) in soil contributes to ecosystem N accumulation, even in old-growth and chronically-fertilized forests once thought to have poor N retention capacity. In old-growth conifer and hardwood stands in Pennsylvania, we tested the hypotheses that biotic and abiotic N immobilization are regulated by N form and forest type. We added 15NH4 +, 15NO2 -, and 15NO3 - to sterile (γ-irradiated) and live organic-horizon soil and define N immobilization as the mass of added 15N remaining in soil following extractions conducted 15 min, 24 h, and 21 days later. Immobilization of NO2 - (19-25% of added N) occurred in sterile soils within 15 min and was little changed thereafter. Tracer NO3 - immobilization was not observed, although soils had been pretreated (refrigerated) so as to quantify the lower limit of immobilization potential. Immobilization of NH4 + (27%) occurred in live conifer soils by 21 days but not in other treatments. In 21-day incubations, tracer N immobilization was greater in NO3 --poor and humic-rich soils. Immobilization was greater in sterile than in live soil, perhaps owing to artifacts of sterilization. Conifer stands exhibited more massive O-horizons, so NO2 - immobilization per unit area was greater in conifer (1. 46 mg N m-2) than hardwood (0. 43 mg N m-2) stands, possibly accounting for lower N leaching from conifer forests. Areal immobilization rates appear to be fast enough to retain all N transformed to NO2 -, so NO2 - production may be a limiting step in soil N retention in old-growth ecosystems.

Original languageEnglish (US)
Pages (from-to)169-186
Number of pages18
JournalBiogeochemistry
Volume111
Issue number1-3
DOIs
StatePublished - Jan 1 2012

All Science Journal Classification (ASJC) codes

  • Environmental Chemistry
  • Water Science and Technology
  • Earth-Surface Processes

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