title: Nitrogen (N) deposition impacts seedling growth of Pinus massoniana via N:P ratio effects and the modulation of adaptive responses to low P (phosphorus).
abstract: BACKGROUND
  In forest ecosystems with phosphorus (P) deficiency, the impact of atmospheric nitrogen (N) deposition on nutritional traits related to P uptake and P use potentially determines plant growth and vegetation productivity.
  
  
  RESULTS
  Two N deposition simulations were combined with three soil P conditions (homogeneous P deficiency with evenly low P; heterogeneous P deficiency with low subsoil P and high topsoil P; high P) using four full-sib families of Masson pine (Pinus massoniana). Under homogeneous P deficiency, N had a low effect on growth due to higher N:P ratios, whereas N-sensitive genotypes had lower N:P ratios and greater N sensitivity. The N effect increased under higher P conditions due to increased P concentration and balanced N:P ratios. An N:P threshold of 12.0-15.0 was detected, and growth was increased by N with an N:P ratio ≤ 12.0 and increased by P with an N:P ratio ≥ 15.0. Under homogeneous P deficiency, increased P use efficiency by N deposition improved growth. Under heterogeneous P deficiency, a greater P deficiency under N deposition due to increased N:P ratios induced greater adaptive responses to low P (root acid phosphatase secretion and topsoil root proliferation) and improved P acquisition and growth.
  
  
  CONCLUSIONS
  N deposition diversely affected seedling growth across different P conditions and genotypes via N:P ratio effects and the modulation of adaptive responses to low P. The positive impact of N on growth was genotype-specific and increased by soil P addition due to balanced N:P ratios. These results indicate the significance of breeding N-sensitive tree genotypes and improving forest soil P status to compensate for increasing N deposition.
authors.affiliation: Research Institute of Subtropical Forestry, Chinese Academy of Forestry, Fu Yang, Zhe Jiang, P. R. China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.forename: Zhichun
authors.initials: Z
authors.lastname: Zhou
authors.forename: Qing
authors.initials: Q
authors.lastname: Yang
mesh_terms: D000222:Adaptation, Physiological; D005838:Genotype; D009584:Nitrogen / Q000378:metabolism*; D010758:Phosphorus / Q000378:metabolism*; D028223:Pinus / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D036226:Seedlings / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D013312:Stress, Physiological
chemical_list: D010758:Phosphorus; D009584:Nitrogen