title: Negative effects of temperature and atmospheric depositions on the seed viability of common juniper (Juniperus communis).
abstract: OBJECTIVE
  Environmental change is increasingly impacting ecosystems worldwide. However, our knowledge about the interacting effects of various drivers of global change on sexual reproduction of plants, one of their key mechanisms to cope with change, is limited. This study examines populations of poorly regenerating and threatened common juniper (Juniperus communis) to determine the influence of four drivers of global change (rising temperatures, nitrogen deposition, potentially acidifying deposition and altering precipitation patterns) on two key developmental phases during sexual reproduction, gametogenesis and fertilization (seed phase two, SP2) and embryo development (seed phase three, SP3), and on the ripening time of seeds.
  
  
  METHODS
  In 42 populations throughout the distribution range of common juniper in Europe, 11,943 seeds of two developmental phases were sampled. Seed viability was determined using seed dissection and related to accumulated temperature (expressed as growing degree-days), nitrogen and potentially acidifying deposition (nitrogen plus sulfur), and precipitation data.
  
  
  RESULTS
  Precipitation had no influence on the viability of the seeds or on the ripening time. Increasing temperatures had a negative impact on the viability of SP2 and SP3 seeds and decreased the ripening time. Potentially acidifying depositions negatively influenced SP3 seed viability, while enhanced nitrogen deposition led to lower ripening times.
  
  
  CONCLUSIONS
  Higher temperatures and atmospheric deposition affected SP3 seeds more than SP2 seeds. However, this is possibly a delayed effect as juniper seeds develop practically independently, due to the absence of vascular communication with the parent plant from shortly after fertilization. It is proposed that the failure of natural regeneration in many European juniper populations might be attributed to climate warming as well as enhanced atmospheric deposition of nitrogen and sulfur.
authors.affiliation: Forest and Nature Lab, Ghent University, Geraardsbergsesteenweg 267, BE-9090 Melle-Gontrode, Belgium.
authors.forename: R
authors.initials: R
authors.lastname: Gruwez
authors.forename: P
authors.initials: P
authors.lastname: De Frenne
authors.forename: A
authors.initials: A
authors.lastname: De Schrijver
authors.forename: O
authors.initials: O
authors.lastname: Leroux
authors.forename: P
authors.initials: P
authors.lastname: Vangansbeke
authors.forename: K
authors.initials: K
authors.lastname: Verheyen
mesh_terms: D001272:Atmosphere / Q000032:analysis; D057231:Climate Change; D017753:Ecosystem; D005060:Europe; D005843:Geography; D018525:Germination; D018653:Juniperus / Q000196:embryology / Q000254:growth & development / Q000502:physiology*; D009584:Nitrogen / Q000378:metabolism*; D018515:Plant Leaves / Q000196:embryology / Q000254:growth & development / Q000502:physiology; D054817:Pollination; D012098:Reproduction; D012639:Seeds / Q000196:embryology / Q000254:growth & development / Q000502:physiology*; D013696:Temperature
chemical_list: D009584:Nitrogen
keywords: Juniperus communis; acidifying deposition; climate change; increasing temperature; juniper; nitrogen deposition; ripening time; seed viability