title: Sensitivity of three tree ferns during their first phase of life to the variation of solar radiation and water availability in a Mexican cloud forest.
abstract: OBJECTIVE
  Regeneration niche differentiation promotes species coexistence and diversity; however, the ecological implications for the initial life phases of the majority of pteridophytes are unknown. We analyzed the sensitivity of gametophytes and juvenile sporophytes of the tree ferns Alsophila firma, Cyathea divergens, and Lophosoria quadripinnata to variation in light and water availability.
  
  
  METHODS
  We evaluated gametophyte desiccation tolerance using saturated salt solutions and gametophyte solar radiation tolerance by direct exposure. We also transplanted juvenile sporophytes in environments with 7% and 23% canopy openness and two watering levels.
  
  
  RESULTS
  The response of photosynthetic efficiency and water content suggest that the gametophytes of the three species require high relative humidity, tolerate direct solar radiation for up to 30 min and that the response is not species-dependent. Sporophyte size and gas exchange were greater in the more open site, but decreased watering had a lesser effect on these variables in the more closed site. Relative growth rate correlated with the net assimilation rate and leaf weight ratio. Juvenile sporophytes of A. firma were more shade tolerant, while those of C. divergens and L. quadripinnata acclimatized to both environments.
  
  
  CONCLUSIONS
  Specialization to humid habitats in the tree fern gametophyte restricts the species to humid forests, while differences in the plasticity of the sporophyte facilitate coexistence of the species.
authors.affiliation: Instituto de Ecología, A.C., Carretera antigua a Coatepec 351, El Haya, Xalapa 91070 Veracruz, México.
authors.forename: Karolina
authors.initials: K
authors.lastname: Riaño
authors.affiliation: Instituto de Ecología, A.C., Carretera antigua a Coatepec 351, El Haya, Xalapa 91070 Veracruz, México oscar.briones@inecol.mx.
authors.forename: Oscar
authors.initials: O
authors.lastname: Briones
mesh_terms: D003890:Desiccation; D029624:Ferns / Q000254:growth & development / Q000502:physiology*; D065928:Forests; D055993:Germ Cells, Plant / Q000254:growth & development; D008800:Mexico; D013045:Species Specificity; D013472:Sunlight; D014197:Trees; D014867:Water / Q000502:physiology*
chemical_list: D014867:Water
keywords: gametophyte; regeneration niche; relative growth rate; stress tolerance; young sporophyte