Overlap in nitrogen sources and redistribution of nitrogen between trees and grasses in a semi-arid savanna

K.V.R. Priyadarshini, H.H.T. Prins, S. de Bie, I.M.A. Heitkonig, S. Woodborne, G. Gort, K. Kirkman, B. Fry, H. de Kroon

Research output: Contribution to journalArticleAcademicpeer-review

6 Citations (Scopus)

Abstract

A key question in savanna ecology is how trees and grasses coexist under N limitation. We used N stable isotopes and N content to study N source partitioning across seasons from trees and associated grasses in a semi-arid savanna. We also used 15N tracer additions to investigate possible redistribution of N by trees to grasses. Foliar stable N isotope ratio (d15N) values were consistent with trees and grasses using mycorrhiza-supplied N in all seasons except in the wet season when they switched to microbially fixed N. The dependence of trees and grasses on mineralized soil N seemed highly unlikely based on seasonal variation in mineralization rates in the Kruger Park region. Remarkably, foliar d15N values were similar for all three tree species differing in the potential for N fixation through nodulation. The tracer experiment showed that N was redistributed by trees to understory grasses in all seasons. Our results suggest that the redistribution of N from trees to grasses and uptake of N was independent of water redistribution. Although there is overlap of N sources between trees and grasses, dependence on biological sources of N coupled with redistribution of subsoil N by trees may contribute to the coexistence of trees and grasses in semi-arid savannas.
Original languageEnglish
Pages (from-to)1107-1116
JournalOecologia
Volume174
Issue number4
DOIs
Publication statusPublished - 2014

Keywords

  • n-15 natural-abundance
  • southern african savanna
  • root activity
  • patterns
  • water
  • availability
  • vegetation
  • physiology
  • isotopes
  • depth

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