Interactive Effects of Vegetation Type and Topographic Position on Nitrogen Availability and Loss in a Temperate Montane Ecosystem

Samantha R. Weintraub, Paul Brooks, Gabriel J. Bowen

Research output: Contribution to journalArticle

6 Scopus citations

Abstract

Determining the fate of deposited nitrogen (N) in natural ecosystems remains a challenge. Heterogeneity of vegetation types and resulting plant–soil feedbacks interact with topo-hydrologic gradients to mediate spatial patterns of N availability and loss, yet net effects of variation in these two factors together across complex terrain remain unclear. Here we measured a suite of N-cycle pools and fluxes in sites that differed factorially in vegetation type (mixed forest vs. herbaceous) and topographic position (upslope vs. downslope) in a protected montane watershed near Salt Lake City, UT. Vegetation type was associated with large variation in N availability—herbaceous sites had larger NO3 pools, higher NO3 :NH4 + ratios, higher nitrification potentials, lower soil C:N values, enriched δ15N values, and lower microbial biomass compared to forests, especially those upslope. Downslope sites tended to exhibit higher N availability and indicators of N-cycle openness, but patterns were moderated by vegetation type. In downslope forest, soil NO3 depth profiles and higher foliar N content suggested trees were accessing deep soil N and transferring it to the surface via litterfall, while more deep soil NO3 but no change in surface or foliar N suggested herbaceous cover was not N limited or deeper N pools were not accessible. Soil NO3 leaching from below the rooting zone closely tracked N availability, revealing a link between N status and hydrologic loss as well as an important role for roots in N retention. NO3 isotopes did not reveal a similar link for gaseous losses (that is, denitrification), instead reflecting nitrification and/or transport dynamics. Together, these results suggest a coupled ecological, topo-hydrologic perspective can help assess the fate of N in complex landscapes.

Original languageEnglish (US)
Pages (from-to)1-16
Number of pages16
JournalEcosystems
DOIs
StateAccepted/In press - Dec 26 2016
Externally publishedYes

Keywords

  • nitrate leaching
  • plant–soil interactions
  • soil nitrogen
  • topographic wetness

ASJC Scopus subject areas

  • Environmental Chemistry
  • Ecology, Evolution, Behavior and Systematics
  • Ecology

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