Does deep soil N availability sustain long-term ecosystem responses to elevated CO2?

Duncan C. Mckinley, Julio C. Romero, Bruce A. Hungate, Bert G. Drake, James P. Megonigal

Research output: Contribution to journalArticle

32 Scopus citations

Abstract

A scrub-oak woodland has maintained higher aboveground biomass accumulation after 11 years of atmospheric CO2 enrichment (ambient + 350 μmol CO2 mol-1), despite the expectation of strong nitrogen (N) limitation at the site. We hypothesized that changes in plant available N and exploitation of deep sources of inorganic N in soils have sustained greater growth at elevated CO2. We employed a suite of assays performed in the sixth and 11th year of a CO2 enrichment experiment designed to assess soil N dynamics and N availability in the entire soil profile. In the 11th year, we found no differences in gross N flux, but significantly greater microbial respiration (P≤0.01) at elevated CO2. Elevated CO2 lowered extractable inorganic N concentrations (P = 0.096) considering the whole soil profile (0-190cm). Conversely, potential net N mineralization, although not significant in considering the entire profile (P = 0.460), tended to be greater at elevated CO2. Ion-exchange resins placed in the soil profile for approximately 1 year revealed that potential N availability at the water table was almost 3 × greater than found elsewhere in the profile, and we found direct evidence using a 15N tracer study that plants took up N from the water table. Increased microbial respiration and shorter mean residence times of inorganic N at shallower depths suggests that enhanced SOM decomposition may promote a sustained supply of inorganic N at elevated CO2. Deep soil N availability at the water table is considerable, and provides a readily available source of N for plant uptake. Increased plant growth at elevated CO2 in this ecosystem may be sustained through greater inorganic N supply from shallow soils and N uptake from deep soil.

Original languageEnglish (US)
Pages (from-to)2035-2048
Number of pages14
JournalGlobal Change Biology
Volume15
Issue number8
DOIs
StatePublished - Jul 15 2009

Keywords

  • Deep soil nitrogen availability
  • Elevated CO
  • Global change
  • Gross N mineralization
  • Nitrogen cycling
  • Progressive nitrogen limitation
  • Rising atmospheric CO
  • Water table

ASJC Scopus subject areas

  • Global and Planetary Change
  • Environmental Chemistry
  • Ecology
  • Environmental Science(all)

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