Biogeochemical indicators of elevated nitrogen deposition in semiarid Mediterranean ecosystems

• Published in: Environmental monitoring and assessment 2014-09, Vol.186 (9), p.5831-5842
• Main Authors: Ochoa-Hueso, Raúl, Arróniz-Crespo, María, Bowker, Matthew A, Maestre, Fernando T, Pérez-Corona, M. Esther, Theobald, Mark R, Vivanco, Marta G, Manrique, Esteban
• Format: Article
• Language: English
• Subjects: Acidification; Air Pollutants - analysis; Atmospheric Protection/Air Quality Control/Air Pollution; Biogeochemistry; Biomonitoring; Bryophyta - chemistry; Cladonia; Climate change; Coniferous forests; Earth and Environmental Science; Ecology; Ecosystem; Ecosystems; Ecotoxicology; Environment; Environmental Management; Environmental Monitoring; Enzymatic activity; enzyme activity; Enzymes; Forests; Geochemistry; Kermes; Lichens; Lichens - chemistry; Monitoring/Environmental Analysis; Mosses; mosses and liverworts; nitrate reductase; Nitrates; Nitrogen; Nitrogen - analysis; nitrogen content; Nitrogen Fixation; phosphorus; Phosphorus - analysis; Physiology; Pinus - chemistry; Pinus halepensis; Pleurochaete squarrosa; Pollutants; pollution; Quercus - chemistry; Quercus coccifera; Ratios; Shrublands; soil; Soil - chemistry; Soil acidification; soil organic carbon; Soils; Spain; Studies; Terrestrial ecosystems
• ISSN: 0167-6369; 1573-2959
• DOI: 10.1007/s10661-014-3822-6

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.