title: Long-term nitrogen deposition linked to reduced water use efficiency in forests with low phosphorus availability.
abstract: The impact of long-term nitrogen (N) deposition is under-studied in phosphorus (P)-limited subtropical forests. We exploited historically collected herbarium specimens to investigate potential physiological responses of trees in three subtropical forests representing an urban-to-rural gradient, across which N deposition has probably varied over the past six decades. We measured foliar [N] and [P] and stable carbon (δ(13) C), oxygen (δ(18) O) and nitrogen (δ(15) N) isotopic compositions in tissue from herbarium specimens of plant species collected from 1947 to 2014. Foliar [N] and N : P increased, and δ(15) N and [P] decreased in the two forests close to urban centers. Consistent with recent studies demonstrating that N deposition in the region is (15) N-depleted, these data suggest that the increased foliar [N] and N : P, and decreased [P], may be attributable to atmospheric deposition and associated enhancement of P limitation. Estimates of intrinsic water use efficiency calculated from foliar δ(13) C decreased by c. 30% from the 1950s to 2014, contrasting with multiple studies investigating similar parameters in N-limited forests. This effect may reflect decreased photosynthesis, as suggested by a conceptual model of foliar δ(13) C and δ(18) O. Long-term N deposition may exacerbate P limitation and mitigate projected increases in carbon stocks driven by elevated CO2 in forests on P-limited soils.
authors.affiliation: College of Geographical Sciences, Fujian Normal University, Fuzhou, 350007, China.|Key Laboratory for Subtropical Mountain Ecology, Fujian Normal University, Fuzhou, 350007, China.
authors.forename: Zhiqun
authors.initials: Z
authors.lastname: Huang
authors.affiliation: College of Forestry, Fujian Agriculture and Forestry University, Fuzhou, 350002, China.
authors.forename: Bao
authors.initials: B
authors.lastname: Liu
authors.affiliation: Scion, PO Box 29237, Fendalton, Christchurch, New Zealand.
authors.forename: Murray
authors.initials: M
authors.lastname: Davis
authors.affiliation: Global Ecology Unit, CREAF-CSIC-UAB, Cerdanyola del Vallès, Catalonia, 08193, Spain.|CREAF, Cerdanyola del Vallès, Catalonia, 08193, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Sardans
authors.affiliation: Global Ecology Unit, CREAF-CSIC-UAB, Cerdanyola del Vallès, Catalonia, 08193, Spain.|CREAF, Cerdanyola del Vallès, Catalonia, 08193, Spain.
authors.forename: Josep
authors.initials: J
authors.lastname: Peñuelas
authors.affiliation: Department of Ecology and Evolutionary Biology, Kansas Biological Survey, University of Kansas, Lawrence, KS, 66047, USA.
authors.forename: Sharon
authors.initials: S
authors.lastname: Billings
mesh_terms: D002247:Carbon Isotopes; D002681:China; D065928:Forests; D005843:Geography; D009584:Nitrogen / Q000378:metabolism*; D009587:Nitrogen Isotopes; D010103:Oxygen Isotopes; D010758:Phosphorus / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism; D014867:Water / Q000378:metabolism*
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D010103:Oxygen Isotopes; D014867:Water; D010758:Phosphorus; D009584:Nitrogen
keywords: P-limited soils; herbarium specimens; nitrogen : phosphorus (N : P); δ13C; δ15N