title: Optimizing nitrogen economy under drought: increased leaf nitrogen is an acclimation to water stress in willow (Salix spp.).
abstract: OBJECTIVE
  The major objective was to identify plant traits functionally important for optimization of shoot growth and nitrogen (N) economy under drought. Although increased leaf N content (area basis) has been observed in dry environments and theory predicts increased leaf N to be an acclimation to drought, experimental evidence for the prediction is rare.
  
  
  METHODS
  A pedigree of 200 full-sibling hybrid willows was pot-grown in a glasshouse in three replicate blocks and exposed to two water regimes for 3 weeks. Drought conditions were simulated as repeated periods of water shortage. The total leaf mass and area, leaf area efficiency (shoot growth per unit leaf area, E(A)), area-based leaf N content (N(A)), total leaf N pool (N(L)) and leaf N efficiency (shoot growth per unit leaf N, E(N)) were assessed.
  
  
  RESULTS
  In the water-stress treatment, shoot biomass growth was N limited in the genotypes with low N(L), but increasingly limited by other factors in the genotypes with greatest N(L). The N(A) was increased by drought, and drought-induced shift in N(A) varied between genotypes (significant G × E). Judged from the E(A)-N(A) relationship, optimal N(A) was 16 % higher in the water-stress compared with the well-watered treatment. Biomass allocation to leaves and shoots varied between treatments, but the treatment response of the leaf : shoot ratio was similar across all genotypes.
  
  
  CONCLUSIONS
  It is concluded that N-uptake efficiency and leaf N efficiency are important traits to improve growth under drought. Increased leaf N content (area basis) is an acclimation to optimize N economy under drought. The leaf N content is an interesting trait for breeding of willow bioenergy crops in a climate change future. In contrast, leaf biomass allocation is a less interesting breeding target to improve yield under drought.
authors: Department of Crop Production Ecology, POB 7043, Swedish University of Agricultural Sciences, Sweden. martin.weih@slu.se
authors: Martin
authors: M
authors: Weih
authors: Lorenzo
authors: L
authors: Bonosi
authors: Luisa
authors: L
authors: Ghelardini
authors: Ann Christin
authors: AC
authors: Rönnberg-Wästljung
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D002678:Chimera; D003681:Dehydration / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D018515:Plant Leaves / Q000737:chemistry / Q000378:metabolism; D018520:Plant Shoots / Q000378:metabolism; D032108:Salix / Q000254:growth & development / Q000378:metabolism*
chemical_list: D009584:Nitrogen