Biogeochemical indicators of elevated nitrogen deposition in semiarid Mediterranean ecosystems

Raúl Ochoa-Hueso*, María Arróniz-Crespo, Matthew A. Bowker, Fernando T. Maestre, M. Esther Pérez-Corona, Mark R. Theobald, Marta G. Vivanco, Esteban Manrique

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

33 Scopus citations


Nitrogen (N) deposition has doubled the natural N inputs received by ecosystems through biological N fixation and is currently a global problem that is affecting the Mediterranean regions. We evaluated the existing relationships between increased atmospheric N deposition and biogeochemical indicators related to soil chemical factors and cryptogam species across semiarid central, southern, and eastern Spain. The cryptogam species studied were the biocrust-forming species Pleurochaete squarrosa (moss) and Cladonia foliacea (lichen). Sampling sites were chosen in Quercus coccifera (kermes oak) shrublands and Pinus halepensis (Aleppo pine) forests to cover a range of inorganic N deposition representative of the levels found in the Iberian Peninsula (between 4.4 and 8.1 kg N ha-1 year-1). We extended the ambient N deposition gradient by including experimental plots to which N had been added for 3 years at rates of 10, 20, and 50 kg N ha -1 year-1. Overall, N deposition (extant plus simulated) increased soil inorganic N availability and caused soil acidification. Nitrogen deposition increased phosphomonoesterase (PME) enzyme activity and PME/nitrate reductase (NR) ratio in both species, whereas the NR activity was reduced only in the moss. Responses of PME and NR activities were attributed to an induced N to phosphorus imbalance and to N saturation, respectively. When only considering the ambient N deposition, soil organic C and N contents were positively related to N deposition, a response driven by pine forests. The PME/NR ratios of the moss were better predictors of N deposition rates than PME or NR activities alone in shrublands, whereas no correlation between N deposition and the lichen physiology was observed. We conclude that integrative physiological measurements, such as PME/NR ratios, measured on sensitive species such as P. squarrosa, can provide useful data for national-scale biomonitoring programs, whereas soil acidification and soil C and N storage could be useful as additional corroborating ecosystem indicators of chronic N pollution.

Original languageEnglish (US)
Pages (from-to)5831-5842
Number of pages12
JournalEnvironmental Monitoring and Assessment
Issue number9
StatePublished - Sep 2014


  • Acidification
  • Biocrusts
  • Bioindicators
  • C and N storage
  • Cryptogams
  • N deposition
  • Nitrate reductase
  • Phosphomonoesterase
  • Semiarid Mediterranean

ASJC Scopus subject areas

  • General Environmental Science
  • Pollution
  • Management, Monitoring, Policy and Law


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