title: Soil nitrogen, and not phosphorus, promotes cluster-root formation in a South American Proteaceae, Embothrium coccineum.
abstract: OBJECTIVE
  Cluster roots are a characteristic root adaptation of Proteaceae species. In South African and Australian species, cluster roots promote phosphorus (P) acquisition from poor soils. In a South American Proteaceae species, where cluster roots have been scarcely studied and their function is unknown, we tested whether cluster-root formation is stimulated by low soil nutrition, in particular low P-availability.
  
  
  METHODS
  Small and large seedlings (< 6- and > 6-months old, respectively) of Embothrium coccineum and soil were collected across four different sites in Patagonia (Chile). We determined cluster-root number and relative mass, and leaf Pi concentration per mass (Pimass) and per area (Piarea) for each seedling, and tested relationships with Olsen-P (OP), sorbed-P (sP) and total nitrogen (N) using generalized linear mixed-effects models and model selection to assess the relative strength of soil and plant drivers.
  
  
  RESULTS
  Best-fit models showed a negative logarithmic relationship between cluster-root number and soil nitrogen (N), and between cluster-root relative mass and both leaf Piarea and soil N, and a positive logarithmic relationship between cluster-root number and leaf Piarea. Cluster-root relative mass was higher in small than in large seedlings.
  
  
  CONCLUSIONS
  Contrary to that found in South African and Australian Proteaceae, cluster roots of E. coccineum do not appear to be driven by soil P, but rather by soil N and leaf Piarea. We suggest that cluster roots are a constitutive and functional trait that allows plants to prevail in poor N soils.
authors.affiliation: Centro de Investigación en Ecosistemas de la Patagonia (CIEP) Conicyt-Regional R10C1003, Universidad Austral de Chile, Camino Baguales s/n, Coyhaique, Chile.
authors.forename: Frida I
authors.initials: FI
authors.lastname: Piper
authors.forename: Gabriela
authors.initials: G
authors.lastname: Baeza
authors.forename: Alejandra
authors.initials: A
authors.lastname: Zúñiga-Feest
authors.forename: Alex
authors.initials: A
authors.lastname: Fajardo
mesh_terms: D000222:Adaptation, Physiological; D002677:Chile; D009584:Nitrogen / Q000378:metabolism*; D010758:Phosphorus / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots / Q000254:growth & development* / Q000378:metabolism; D039105:Proteaceae / Q000254:growth & development* / Q000378:metabolism; D036226:Seedlings / Q000254:growth & development* / Q000378:metabolism; D012987:Soil / Q000737:chemistry*
chemical_list: D012987:Soil; D010758:Phosphorus; D009584:Nitrogen
keywords: Embothrium coccineum; Olsen–P; establishment; intraspecific variation; leaf phosphate; proteoid roots; succession; volcanic soils