title: Photosynthetic Light Responses May Explain Vertical Distribution of Hymenophyllaceae Species in a Temperate Rainforest of Southern Chile.
abstract: Some epiphytic Hymenophyllaceae are restricted to lower parts of the host (< 60 cm; 10-100 μmol photons m(-2) s(-1)) in a secondary forest of Southern Chile; other species occupy the whole host height (≥ 10 m; max PPFD > 1000 μmol photons m(-2) s(-1)). Our aim was to study the photosynthetic light responses of two Hymenophyllaceae species in relation to their contrasting distribution. We determined light tolerance of Hymenoglossum cruentum and Hymenophyllum dentatum by measuring gas exchange, PSI and PSII light energy partitioning, NPQ components, and pigment contents. H. dentatum showed lower maximum photosynthesis rates (A max) than H. cruentum, but the former species kept its net rates (An) near Amax across a wide light range. In contrast, in the latter one, An declined at PPFDs > 60 μmol photons m(-2) s(-1). H. cruentum, the shadiest plant, showed higher chlorophyll contents than H. dentatum. Differences in energy partitioning at PSI and PSII were consistent with gas exchange results. H. dentatum exhibited a higher light compensation point of the partitioning of absorbed energy between photochemical Y(PSII) and non-photochemical Y(NPQ) processes. Hence, both species allocated energy mainly toward photochemistry instead of heat dissipation at their light saturation points. Above saturation, H. cruentum had higher heat dissipation than H. dentatum. PSI yield (YPSI) remained higher in H. dentatum than H. cruentum in a wider light range. In both species, the main cause of heat dissipation at PSI was a donor side limitation. An early dynamic photo-inhibition of PSII may have caused an over reduction of the Qa+ pool decreasing the efficiency of electron donation to PSI. In H. dentatum, a slight increase in heat dissipation due to acceptor side limitation of PSI was observed above 300 μmol photons m(-2)s(-1). Differences in photosynthetic responses to light suggest that light tolerance and species plasticity could explain their contrasting vertical distribution.
authors.affiliation: Departamento de Ciencias Biológicas y Químicas, Facultad de Ciencia, Universidad San Sebastián, Cruz 1577, Concepción, Chile.
authors.forename: María José
authors.initials: MJ
authors.lastname: Parra
authors.affiliation: Departamento de Botánica, Facultad de Ciencias Naturales y Oceanográficas, Universidad de Concepción, Casilla 160-C, Concepción, Chile.|Laboratorio de Fisiología y Biología Molecular Vegetal, Departamento de Ciencias Agronómicas y Recursos Naturales. Facultad de Ciencias Agropecuarias y Forestales & Center of Plant, Soil Interactions and Natural Resources Biotechnology, Scientific and Technological Bioresource Nucleus, Universidad de La Frontera, Casilla 54-D, Temuco, Chile.
authors.forename: Karina I
authors.initials: KI
authors.lastname: Acuña
authors.affiliation: Departamento de Botánica, Facultad de Ciencias Naturales y Oceanográficas, Universidad de Concepción, Casilla 160-C, Concepción, Chile.|Instituto de Ecología y Biodiversidad (IEB), Casilla 653, Santiago, Chile.
authors.forename: Angela
authors.initials: A
authors.lastname: Sierra-Almeida
authors.affiliation: Instituto de Ecología y Biodiversidad (IEB), Casilla 653, Santiago, Chile.|Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Chile.
authors.forename: Camila
authors.initials: C
authors.lastname: Sanfuentes
authors.affiliation: Departamento de Botánica, Facultad de Ciencias Naturales y Oceanográficas, Universidad de Concepción, Casilla 160-C, Concepción, Chile.
authors.forename: Alfredo
authors.initials: A
authors.lastname: Saldaña
authors.affiliation: Departamento de Botánica, Facultad de Ciencias Naturales y Oceanográficas, Universidad de Concepción, Casilla 160-C, Concepción, Chile.
authors.forename: Luis J
authors.initials: LJ
authors.lastname: Corcuera
authors.affiliation: Laboratorio de Fisiología y Biología Molecular Vegetal, Departamento de Ciencias Agronómicas y Recursos Naturales. Facultad de Ciencias Agropecuarias y Forestales & Center of Plant, Soil Interactions and Natural Resources Biotechnology, Scientific and Technological Bioresource Nucleus, Universidad de La Frontera, Casilla 54-D, Temuco, Chile.
authors.forename: León A
authors.initials: LA
authors.lastname: Bravo
mesh_terms: D000222:Adaptation, Physiological; D002677:Chile; D002734:Chlorophyll / Q000378:metabolism*; D004579:Electron Transport; D029624:Ferns / Q000502:physiology* / Q000528:radiation effects*; D008027:Light; D010777:Photochemistry; D010788:Photosynthesis / Q000502:physiology*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D018515:Plant Leaves / Q000502:physiology / Q000528:radiation effects; D065947:Rainforest
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D002734:Chlorophyll