Ecosystem Ecology - Original Paper

Oecologia

, Volume 156, Issue 4, pp 861-870

Open Access This content is freely available online to anyone, anywhere at any time.

Foliar δ15N values characterize soil N cycling and reflect nitrate or ammonium preference of plants along a temperate grassland gradient

  • Ansgar KahmenAffiliated withMax Planck Institute for BiogeochemistryCenter for Stable Isotope Biogeochemistry, Department of Integrative Biology, University of California Email author 
  • , Wolfgang WanekAffiliated withDepartment of Chemical Ecology and Ecosystem Research, University of Vienna
  • , Nina BuchmannAffiliated withMax Planck Institute for BiogeochemistryInstitute of Plant Sciences, ETH Zurich

Abstract

The natural abundance of stable 15N isotopes in soils and plants is potentially a simple tool to assess ecosystem N dynamics. Several open questions remain, however, in particular regarding the mechanisms driving the variability of foliar δ15N values of non-N2 fixing plants within and across ecosystems. The goal of the work presented here was therefore to: (1) characterize the relationship between soil net mineralization and variability of foliar Δδ15N (δ15Nleaf − δ15Nsoil) values from 20 different plant species within and across 18 grassland sites; (2) to determine in situ if a plant’s preference for NO 3 or NH 4 + uptake explains variability in foliar Δδ15N among different plant species within an ecosystem; and (3) test if variability in foliar Δδ15N among species or functional group is consistent across 18 grassland sites. Δδ15N values of the 20 different plant species were positively related to soil net mineralization rates across the 18 sites. We found that within a site, foliar Δδ15N values increased with the species’ NO 3 to NH 4 + uptake ratios. Interestingly, the slope of this relationship differed in direction from previously published studies. Finally, the variability in foliar Δδ15N values among species was not consistent across 18 grassland sites but was significantly influenced by N mineralization rates and the abundance of a particular species in a site. Our findings improve the mechanistic understanding of the commonly observed variability in foliar Δδ15N among different plant species. In particular we were able to show that within a site, foliar δ15N values nicely reflect a plant’s N source but that the direction of the relationship between NO 3 to NH 4 + uptake and foliar Δδ15N values is not universal. Using a large set of data, our study highlights that foliar Δδ15N values are valuable tools to assess plant N uptake patterns and to characterize the soil N cycle across different ecosystems.

Keywords

Stable isotopes Mineral nutrition Competition Nitrogen Mineralization Biodiversity