title: Thermal niche for in situ seed germination by Mediterranean mountain streams: model prediction and validation for Rhamnus persicifolia seeds.
abstract: OBJECTIVE
  Mediterranean mountain species face exacting ecological conditions of rainy, cold winters and arid, hot summers, which affect seed germination phenology. In this study, a soil heat sum model was used to predict field emergence of Rhamnus persicifolia, an endemic tree species living at the edge of mountain streams of central eastern Sardinia.
  
  
  METHODS
  Seeds were incubated in the light at a range of temperatures (10-25 and 25/10 °C) after different periods (up to 3 months) of cold stratification at 5 °C. Base temperatures (Tb), and thermal times for 50 % germination (θ50) were calculated. Seeds were also buried in the soil in two natural populations (Rio Correboi and Rio Olai), both underneath and outside the tree canopy, and exhumed at regular intervals. Soil temperatures were recorded using data loggers and soil heat sum (°Cd) was calculated on the basis of the estimated Tb and soil temperatures.
  
  
  RESULTS
  Cold stratification released physiological dormancy (PD), increasing final germination and widening the range of germination temperatures, indicative of a Type 2 non-deep PD. Tb was reduced from 10·5 °C for non-stratified seeds to 2·7 °C for seeds cold stratified for 3 months. The best thermal time model was obtained by fitting probit germination against log °Cd. θ50 was 2·6 log °Cd for untreated seeds and 2·17-2·19 log °Cd for stratified seeds. When θ50 values were integrated with soil heat sum estimates, field emergence was predicted from March to April and confirmed through field observations.
  
  
  CONCLUSIONS
  Tb and θ50 values facilitated model development of the thermal niche for in situ germination of R. persicifolia. These experimental approaches may be applied to model the natural regeneration patterns of other species growing on Mediterranean mountain waterways and of physiologically dormant species, with overwintering cold stratification requirement and spring germination.
authors.affiliation: Centro Conservazione Biodiversità (CCB), Dipartimento di Scienze della Vita e dell'Ambiente, Università degli Studi di Cagliari, Viale Sant'Ignazio da Laconi, 11-13, Cagliari, 09123, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Porceddu
authors.forename: Efisio
authors.initials: E
authors.lastname: Mattana
authors.forename: Hugh W
authors.initials: HW
authors.lastname: Pritchard
authors.forename: Gianluigi
authors.initials: G
authors.lastname: Bacchetta
mesh_terms: D017753:Ecosystem; D018525:Germination; D019083:Mediterranean Region; D008954:Models, Biological; D057445:Plant Dormancy; D031955:Rhamnus / Q000502:physiology*; D045483:Rivers; D012639:Seeds / Q000502:physiology*; D013696:Temperature
keywords: Base temperature; Rhamnaceae; Rhamnus persicifolia; climate change; cold stratiﬁcation; physiological dormancy; seed germination model; soil heat sum; thermal time