Plant nitrogen capture from organic matter as affected by spatial dispersion, interspecific competition and mycorrhizal colonization

The capture of nitrogen (N) by plants from N-rich complex organic material differing in spatial (uniform dispersion or discrete patches) heterogeneity was measured, as well as the subsequent impact on N capture of the addition of a mycorrhizal inoculum (Glomus hoi). The organic material was dual-labelled with N-15 and C-13 to follow plant uptake of N (as N-15) and to determine the amounts of original C-13 and N-15 which remained in the soil at harvest. The organic material was added to microcosm units containing Lolium perenne or Plantago lanceolata in intra or interspecific competition. Plant N capture from the dispersed organic material was more than twice that from the discrete patch (dispersed: 17%; discrete: 8%). There was no effect of species composition or the mycorrhizal inoculum on total plant N capture except when in interspecific plant competition. Here, N capture was dependent on the root length produced and was always higher when the mycorrhizal inoculum was present. Mycorrhizal colonization increased N capture from the organic material when in interspecific plant competition but not in monoculture.