Browsing by Author "Saldana, Alfredo"

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    Climbing plants in a temperate rainforest understorey: searching for high light or coping with deep shade?
    (2011) Valladares, Fernando; Gianoli, Ernesto; Saldana, Alfredo
    Background and Aims While the climbing habit allows vines to reach well-lit canopy areas with a minimum investment in support biomass, many of them have to survive under the dim understorey light during certain stages of their life cycle. But, if the growth/survival trade-off widely reported for trees hold for climbing plants, they cannot maximize both light-interception efficiency and shade avoidance (i.e. escaping from the understorey). The seven most important woody climbers occurring in a Chilean temperate evergreen rainforest were studied with the hypothesis that light-capture efficiency of climbers would be positively associated with their abundance in the understorey.
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    Costs versus risks: Architectural changes with changing light quantity and quality in saplings of temperate rainforest trees of different shade tolerance
    (2012) Valladares, Fernando; Saldana, Alfredo; Gianoli, Ernesto
    Light requirements and functional strategies of plants to cope with light heterogeneity in the field have a strong influence on community structure and dynamics. Shade intolerant plants often show a shade avoidance strategy involving a phytochrome-mediated stem elongation in response to changes in red : far red ratio, while shade-tolerant plants typically harvest light very efficiently. We measured plant size, stem diameter, internode and leaf lengths in randomly chosen saplings of 11 woody species differing in their shade tolerance in both a secondary forest and an old-growth temperate evergreen rainforest in southern Chile. We also recorded the irradiance spectrum and the diffuse and direct light availabilities at each sampling point. Significant differences were found for the mean light environment of the saplings of each species, which also differed in basal stem diameter, internode length and leaf length, but not in plant height. Both plant slenderness (plant height/stem diameter) and mean internode length increased with increasing light availability, but no relationship was found between any of these two traits and red : far red ratio. The change in plant slenderness with light availability was of lesser magnitude with increasing shade tolerance of the species, while internode change with light availability increased with increasing shade tolerance of the species. Shade tolerators afford higher costs (thicker stems and plants), which render more biomechanically robust plants, and respond more to the light environment in a trait strongly influencing light interception (internode length) than shade intolerant species. By contrast, less shade-tolerant plants afforded higher risks with a plastic response to escape from the understorey by making thinner plants that were biomechanically weaker and poorer light interceptors. Thus, species differing in their shade tolerances do differ in their plastic responses to light. Our results contribute to explain plant coexistence in heterogeneous light environments by improving our mechanistic understanding of species responses to light.
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    Distribution and abundance of vines along the light gradient in a southern temperate rain forest
    (2010) Gianoli, Ernesto; Saldana, Alfredo; Jimenez-Castillo, Mylthon; Valladares, Fernando
    Question: Are vines light-demanding species?
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    Ecophysiological Traits May Explain the Abundance of Climbing Plant Species across the Light Gradient in a Temperate Rainforest
    (2012) Gianoli, Ernesto; Saldana, Alfredo; Jimenez-Castillo, Mylthon
    Climbing plants are a key component of rainforests, but mechanistic approaches to their distribution and abundance are scarce. In a southern temperate rainforest, we addressed whether the dominance of climbing plants across light environments is associated with the expression of ecophysiological traits. In mature forest and canopy gaps, we measured leaf size, specific leaf area, photosynthetic rate, and dark respiration in six of the most abundant woody vines. Mean values of traits and their phenotypic change (%) between mature forest and canopy gaps were predictor variables. Leaf size and specific leaf area were not significantly associated with climbing plant dominance. Variation in gas-exchange traits between mature forest and canopy gaps explained, at least partly, the dominance of climbers in this forest. A greater increase in photosynthetic rate and a lower increase in dark respiration rate when canopy openings occur were related to the success of climbing plant species. Dominant climbers showed a strategy of maximizing exploitation of resource availability but minimizing metabolic costs. Results may reflect phenotypic plasticity or genetic differentiation in ecophysiological traits between light environments. It is suggested that the dominant climbers in this temperate rainforest would be able to cope with forest clearings due to human activities.
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    Forests are not immune to plant invasions: phenotypic plasticity and local adaptation allow Prunella vulgaris to colonize a temperate evergreen rainforest
    (2011) Godoy, Oscar; Saldana, Alfredo; Fuentes, Nicol; Valladares, Fernando; Gianoli, Ernesto
    In the South American temperate evergreen rainforest (Valdivian forest), invasive plants are mainly restricted to open sites, being rare in the shaded understory. This is consistent with the notion of closed-canopy forests as communities relatively resistant to plant invasions. However, alien plants able to develop shade tolerance could be a threat to this unique forest. Phenotypic plasticity and local adaptation are two mechanisms enhancing invasiveness. Phenotypic plasticity can promote local adaptation by facilitating the establishment and persistence of invasive species in novel environments. We investigated the role of these processes in the recent colonization of Valdivian forest understory by the perennial alien herb Prunella vulgaris from nearby populations in open sites. Using reciprocal transplants, we found local adaptation between populations. Field data showed that the shade environment selected for taller plants and greater specific leaf areas. We found population differentiation and within-population genetic variation in both mean values and reaction norms to light variation of several ecophysiological traits in common gardens from seeds collected in sun and shade populations. The colonization of the forest resulted in a reduction of plastic responses to light variation, which is consistent with the occurrence of genetic assimilation and suggests that P. vulgaris individuals adapted to the shade have reduced probabilities to return to open sites. All results taken together confirm the potential for rapid evolution of shade tolerance in P. vulgaris and suggest that this alien species may pose a threat to the native understory flora of Valdivian forest.