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Seedling growth responses to light and mineral N form are predicted by species ecologies and can help explain tree diversity

Walters, Michael B., Willis, John L., Gottschalk, Kurt W.
Canadian journal of forest research = 2014 v.44 no.11 pp. 1356-1368
Coniferophyta, Magnoliophyta, ammonium nitrogen, canopy, energy requirements, hardwood forests, nitrate nitrogen, nitrates, nitrogen, phylogeny, planting, seedling growth, shade tolerance, soil, trees, Michigan
Tree species distributions and diversity could be explained by rank changes in performance over multiple spatiotemporal resource gradients, i.e., resource partitioning. For 14 species planted in 45 harvest gap and closed canopy locations in a mesic northern hardwood forest community, Michigan, USA, we asked the following questions: (i) are species growth responses to light, nitrogen (N), or N form (ammonium vs. nitrate) related to their ecological distributions and phylogenies? and (ii) is there evidence of growth-based resource partitioning over measured resource gradients? Growth responses to the N form were consistent with both differences in uptake energy requirements between N forms and their availability through succession and across fertility gradients; height growth was negatively related to the species shade-tolerance score, especially in high light, i.e., shade-intolerant species responded to soil nitrate-N and shade-tolerant species responded to ammonium-N; fertile soil associated species responded to nitrate-N and infertile soil associated species to ammonium-N; and gymnosperms responded to ammonium-N and angiosperm responses varied. Modeled growth responses to resources showed only modest evidence for rank changes over resource gradients, with N contributing less to rank changes than light. Thus, growth responses to resources were accurately predicted by species ecology and (or) phylogeny; however, there was only modest support for the notion that growth-based resource partitioning underlies community-scale diversity in a northern hardwood forest.