title: Aridity modulates N availability in arid and semiarid Mediterranean grasslands.
abstract: While much is known about the factors that control each component of the terrestrial nitrogen (N) cycle, it is less clear how these factors affect total N availability, the sum of organic and inorganic forms potentially available to microorganisms and plants. This is particularly true for N-poor ecosystems such as drylands, which are highly sensitive to climate change and desertification processes that can lead to the loss of soil nutrients such as N. We evaluated how different climatic, abiotic, plant and nutrient related factors correlate with N availability in semiarid Stipa tenacissima grasslands along a broad aridity gradient from Spain to Tunisia. Aridity had the strongest relationship with N availability, suggesting the importance of abiotic controls on the N cycle in drylands. Aridity appeared to modulate the effects of pH, plant cover and organic C (OC) on N availability. Our results suggest that N transformation rates, which are largely driven by variations in soil moisture, are not the direct drivers of N availability in the studied grasslands. Rather, the strong relationship between aridity and N availability could be driven by indirect effects that operate over long time scales (decades to millennia), including both biotic (e.g. plant cover) and abiotic (e.g. soil OC and pH). If these factors are in fact more important than short-term effects of precipitation on N transformation rates, then we might expect to observe a lagged decrease in N availability in response to increasing aridity. Nevertheless, our results suggest that the increase in aridity predicted with ongoing climate change will reduce N availability in the Mediterranean basin, impacting plant nutrient uptake and net primary production in semiarid grasslands throughout this region.
authors.affiliation: Departamento Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, Sevilla, Spain. mdelbaq@upo.es
authors.forename: Manuel
authors.initials: M
authors.lastname: Delgado-Baquerizo
authors.forename: Fernando T
authors.initials: FT
authors.lastname: Maestre
authors.forename: Antonio
authors.initials: A
authors.lastname: Gallardo
authors.forename: José L
authors.initials: JL
authors.lastname: Quero
authors.forename: Victoria
authors.initials: V
authors.lastname: Ochoa
authors.forename: Miguel
authors.initials: M
authors.lastname: García-Gómez
authors.forename: Cristina
authors.initials: C
authors.lastname: Escolar
authors.forename: Pablo
authors.initials: P
authors.lastname: García-Palacios
authors.forename: Miguel
authors.initials: M
authors.lastname: Berdugo
authors.forename: Enrique
authors.initials: E
authors.lastname: Valencia
authors.forename: Beatriz
authors.initials: B
authors.lastname: Gozalo
authors.forename: Zouhaier
authors.initials: Z
authors.lastname: Noumi
authors.forename: Mchich
authors.initials: M
authors.lastname: Derak
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Wallenstein
mesh_terms: D002244:Carbon / Q000032:analysis; D003889:Desert Climate; D006863:Hydrogen-Ion Concentration; D009584:Nitrogen / Q000032:analysis; D058458:Nitrogen Cycle; D006109:Poaceae; D012987:Soil / Q000032:analysis / Q000737:chemistry*; D013030:Spain; D014416:Tunisia
chemical_list: D012987:Soil; D002244:Carbon; D009584:Nitrogen
references.citation: Science. 2007 May 11;316(5826):847-51
references.pmid: 17495163
references.citation: Ecology. 2007 Aug;88(8):2105-13
references.pmid: 17824441
references.citation: Oecologia. 2009 Mar;159(3):571-81
references.pmid: 19034525
references.citation: Ecology. 2006 Aug;87(8):2047-57
references.pmid: 16937644
references.citation: Ecol Lett. 2009 Sep;12(9):930-41
references.pmid: 19638041
references.citation: Ecology. 2007 Jun;88(6):1386-94
references.pmid: 17601131
references.citation: Sci Total Environ. 2008 Dec 15;407(1):692-7
references.pmid: 18930514
references.citation: Science. 2012 Jan 13;335(6065):214-8
references.pmid: 22246775
references.citation: PLoS One. 2012;7(12):e51193
references.pmid: 23236451
references.citation: FEMS Microbiol Ecol. 2010 Jun;72(3):395-406
references.pmid: 20298502
references.citation: Oecologia. 2004 Oct;141(2):221-35
references.pmid: 14986096
references.citation: Oecologia. 1998 Feb;113(4):519-529
references.pmid: 28308032
references.citation: Oecologia. 2001 Aug;128(3):431-442
references.pmid: 24549913