title: Nitrogen addition significantly affects forest litter decomposition under high levels of ambient nitrogen deposition.
abstract: BACKGROUND
  Forest litter decomposition is a major component of the global carbon (C) budget, and is greatly affected by the atmospheric nitrogen (N) deposition observed globally. However, the effects of N addition on forest litter decomposition, in ecosystems receiving increasingly higher levels of ambient N deposition, are poorly understood.
  
  
  RESULTS
  We conducted a two-year field experiment in five forests along the western edge of the Sichuan Basin in China, where atmospheric N deposition was up to 82-114 kg N ha(-1) in the study sites. Four levels of N treatments were applied: (1) control (no N added), (2) low-N (50 kg N ha(-1) year(-1)), (3) medium-N (150 kg N ha(-1) year(-1)), and (4) high-N (300 kg N ha(-1) year(-1)), N additions ranging from 40% to 370% of ambient N deposition. The decomposition processes of ten types of forest litters were then studied. Nitrogen additions significantly decreased the decomposition rates of six types of forest litters. N additions decreased forest litter decomposition, and the mass of residual litter was closely correlated to residual lignin during the decomposition process over the study period. The inhibitory effect of N addition on litter decomposition can be primarily explained by the inhibition of lignin decomposition by exogenous inorganic N. The overall decomposition rate of ten investigated substrates exhibited a significant negative linear relationship with initial tissue C/N and lignin/N, and significant positive relationships with initial tissue K and N concentrations; these relationships exhibited linear and logarithmic curves, respectively.
  
  
  CONCLUSIONS
  This study suggests that the expected progressive increases in N deposition may have a potential important impact on forest litter decomposition in the study area in the presence of high levels of ambient N deposition.
authors.affiliation: College of Forestry, Sichuan Agricultural University, Ya'an, Sichuan, P.R. China.
authors.forename: Li-Hua
authors.initials: LH
authors.lastname: Tu
authors.affiliation: College of Forestry, Sichuan Agricultural University, Ya'an, Sichuan, P.R. China.
authors.forename: Hong-Ling
authors.initials: HL
authors.lastname: Hu
authors.affiliation: College of Forestry, Sichuan Agricultural University, Ya'an, Sichuan, P.R. China.
authors.forename: Gang
authors.initials: G
authors.lastname: Chen
authors.affiliation: College of Forestry, Sichuan Agricultural University, Ya'an, Sichuan, P.R. China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Peng
authors.affiliation: College of Forestry, Sichuan Agricultural University, Ya'an, Sichuan, P.R. China.
authors.forename: Yin-Long
authors.initials: YL
authors.lastname: Xiao
authors.affiliation: College of Forestry, Sichuan Agricultural University, Ya'an, Sichuan, P.R. China.
authors.forename: Ting-Xing
authors.initials: TX
authors.lastname: Hu
authors.affiliation: College of Forestry, Sichuan Agricultural University, Ya'an, Sichuan, P.R. China.
authors.forename: Jian
authors.initials: J
authors.lastname: Zhang
authors.affiliation: College of Forestry, Sichuan Agricultural University, Ya'an, Sichuan, P.R. China.
authors.forename: Xian-Wei
authors.initials: XW
authors.lastname: Li
authors.affiliation: Maize Research Institute, Sichuan Agricultural University Chengdu Campus, Wenjiang District, Chengdu, Sichuan, P.R. China ; Personnel Department, Sichuan Agricultural University, Ya'an, Sichuan, P.R. China.
authors.forename: Li
authors.initials: L
authors.lastname: Liu
authors.affiliation: College of Horticulture, Sichuan Agricultural University, Ya'an, Sichuan, P.R. China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Tang
mesh_terms: D002681:China; D017753:Ecosystem; D008031:Lignin / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism* / Q000494:pharmacology*; D018515:Plant Leaves / Q000187:drug effects / Q000502:physiology*; D011891:Rain; D014197:Trees / Q000502:physiology*
chemical_list: D008031:Lignin; D009584:Nitrogen