DSpace Angular :: Browsing by Author "Gianoli, Ernesto"

Browsing by Author "Gianoli, Ernesto"

Now showing 1 - 20 of 30

Abundance of climbing plants in a southern temperate rain forest: host tree characteristics or light availability?
(2009) Carrasco-Urra, Fernando; Gianoli, Ernesto
Question
Anthropogenic fire drives the evolution of seed traits
(2011) Gomez-Gonzalez, Susana; Torres-Diaz, Cristian; Bustos-Schindler, Carlos; Gianoli, Ernesto
Fire is a major disturbance affecting ecosystems worldwide. Phylogenetic studies have shown that the evolution of seed persistence (fire resistance) is associated with fire frequency or severity. However, the existence of specific seed traits resulting from natural selection mediated by fire remains a key question in plant evolution. We evaluated the role of fire in the evolution of seed traits from a microevolutionary perspective, using as a study system a native forb from the Chilean matorral, where fire is a novel, anthropogenic disturbance. We show that anthropogenic fires are shaping the evolution of seed traits such as pubescence and shape. Among-population variation in seed pubescence, shape, and pericarp thickness was strongly associated with fire frequency, and within a population, fire selected those plants with more pubescent seeds, thicker pericarps, and less rounded seeds. Seed pubescence and shape were shown to be heritable traits. Our findings provide insights into the understanding of the evolution of seed traits in fire-prone environments and demonstrate that human-made fires can be driving evolutionary changes in plant species from ecosystems where fires do not occur naturally.
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.
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.
Counteractive biomass allocation responses to drought and damage in the perennial herb Convolvulus demissus
(2010) Quezada, Ivan M.; Gianoli, Ernesto
Herbivory and water shortage are key ecological factors affecting plant performance. While plant compensatory responses to herbivory include reallocation of biomass from below-ground to above-ground structures, plant responses to reduced soil moisture involve increased biomass allocation to roots and a reduction in the number and size of leaves. In a greenhouse study we evaluated the effects of experimental drought and leaf damage on biomass allocation in Convolvulus demissus (Convolvulaceae), a perennial herb distributed in central Chile, where it experiences summer drought typical of Mediterranean ecosystems and defoliation by leaf beetles and livestock. The number of leaves and internode length were unaffected by the experimental treatments. The rest of plant traits showed interaction of effects. We detected that drought counteracted some plant responses to damage. Thus, only in the control watering environment was it observed that damaged plants produced more stems, even after correcting for main stem length (index of architecture). In the cases of shoot : root ratio, relative shoot biomass and relative root biomass we found that the damage treatment counteracted plant responses to drought. Thus, while undamaged plants under water shortage showed a significant increase in root relative biomass and a significant reduction in both shoot : root ratio and relative shoot biomass, none of these responses to drought was observed in damaged plants. Total plant biomass increased in response to simulated herbivory, apparently due to greater shoot size, and in response to drought, presumably due to greater root size. However, damaged plants under experimental drought had the same total biomass as control plants. Overall, our results showed counteractive biomass allocation responses to drought and damage in C. demissus. Further research must address the fitness consequences under field conditions of the patterns found. This would be of particular importance because both current and expected climatic trends for central Chile indicate increased aridity.
Crassulacean acid metabolism photosynthesis in Bromeliaceae: an evolutionary key innovation
(2011) Quezada, Ivan M.; Gianoli, Ernesto
Crassulacean acid metabolism (CAM) is a photosynthetic pathway that significantly increases water use efficiency in plants. It has been proposed that CAM photosynthesis, which evolved from the ancestral C3 pathway, has played a role in the diversification of some prominent plant groups because it may have allowed them to colonize and successfully spread into arid or semi-arid environments. However, the hypothesis that CAM photosynthesis constitutes an evolutionary key innovation, thereby enhancing diversification rates of the clades possessing it, has not been evaluated quantitatively. We tested whether CAM photosynthesis is a key innovation in the Bromeliaceae, a large and highly diversified plant family that has successfully colonized arid environments. We identified five pairs of sister groups with and without the CAM feature, including 31 genera and over 2000 species. In all five cases, the clades with CAM photosynthesis were more diverse than their C3 counterparts. We provide quantitative evidence that the evolution of CAM photosynthesis is significantly associated with increased diversification in Bromeliaceae and thus constitutes an evolutionary key innovation. We also found preliminary evidence of an association between the CAM pathway and growth habit in bromeliads, with terrestrial species being more likely to show CAM photosynthesis than epiphytic species. To our knowledge, this is the first case of a physiological attribute shown to be a key innovation in plants. (C) 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104, 480-486.
Damage and shade enhance climbing and promote associational resistance in a climbing plant
(2008) Gonzalez-Teuber, Marcia; Gianoli, Ernesto
1. Associational resistance occurs when one plant species gains protection from its consumers by association with a defended species. In semi-arid ecosystems of Chile, the perennial herb Convolvulus chilensis (Convolvulaceae) suffers heavy herbivory by small mammals when growing prostrate but plants seem to be protected when they are climbing onto cacti or thorny shrubs (nurse species).
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?
Drought and leaf damage limit the search for support in the climbing plant Ipomoea purpurea (L.) Roth (Convolvulaceae)
(2011) Atala, Cristian; Cordero, Cristian; Gianoli, Ernesto
There is evidence that some climbing plants increase their twining rate after leaf damage, thus avoiding ground herbivores, and that drought limits this induced response. However, it is unknown whether leaf damage and drought affect the search for support, an ecologically relevant process for climbing plants. We evaluated the combined effect of drought and leaf damage on support searching in the twining vine Ipomoea pupurea (Convolvulaceae). Plants were assigned to a combination of three watering treatments (regular watering, moderate drought, and severe drought) and two damage treatments (control and 50% defoliation). We placed a stake at 15 cm from the stem and recorded the time to successful twining (360 degrees turn). We also measured some plant functional traits to explore possible mechanisms. Leaf damage decreased time to successful twining in all treatments with the exception of severe drought. Severe drought decreased plant growth, particularly when combined with leaf damage. In nature, climbing plants are usually not in contact with a support in the early stages. The searching behavior seems to increase with leaf damage, but it is restricted by water shortage. Plants experiencing both leaf damage and severe drought will be less likely to find a support, resulting in higher probability of further leaf damage.
DROUGHT LIMITS INDUCED TWINING BY LEAF DAMAGE IN THE CLIMBING PLANT IPOMOEA PURPUREA (L.) ROTH (CONVOLVULACEAE)
(2009) Atala, Cristian; Gianoli, Ernesto
The environment may limit the expression of induced responses to herbivory, Such as increased chemical or physical defenses. Recent studies in climbing plants have shown that leaf damage induces twining. This response may confer protection against ground herbivores in the field. We addressed the effect of drought oil the induced twining of the annual vine Ipomoea purpurea (Convolvulaceae), which can experience drought stress in natural conditions. In a greenhouse experiment, we recorded twining rate (proportion of plants successfully climbing at a given time) of damaged and undamaged individuals of I. purpurea Subjected to control watering and water shortage treatments. We also estimated stem growth rate and stem water content in experimental plants, just after the evaluation of climbing Success. Plants in the drought treatment showed reduced twining induction by leaf damage compared to control plants. Neither stem growth nor stem water content were affected by leaf damage or drought. Results Suggest that drought constrains the induced twining through mechanisms not directly related to stein growth and water content. It is Suggested that drought might trigger signals that counteract those elicited by leaf damage. The induced twining may be an advantage in the presence of ground herbivores, but the environmental susceptibility of this response may limit its ecological significance.
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.
Effect of water availability on tolerance of leaf damage in tall morning glory, Ipomoea purpurea
(2009) Atala, Cristian; Gianoli, Ernesto
Resource availability may limit plant tolerance of herbivory. To predict the effect of differential resource availability on plant tolerance, the limiting resource model (LRM) considers which resource limits plant fitness and which resource is mostly affected by herbivore damage. We tested the effect of experimental drought on tolerance of leaf damage in Ipomoea purpurea, which is naturally exposed to both leaf damage and summer drought. To seek mechanistic explanations, we also measured several morphological, allocation and gas exchange traits. In this case, LRM predicts that tolerance would be the same in both water treatments. Plants were assigned to a combination of two water treatments (control and low water) and two damage treatments (50% defoliation and undamaged). Plants showed tolerance of leaf damage, i.e., a similar number of fruits were produced by damaged and undamaged plants, only in control water. Whereas experimental drought affected all plant traits, leaf damage caused plants to show a greater leaf trichome density and reduced shoot biomass, but only in low water. It is suggested that the reduced fitness (number of fruits) of damaged plants in low water was mediated by the differential reduction of shoot biomass, because the number of fruits per shoot biomass was similar in damaged and undamaged plants. Alternative but less likely explanations include the opposing direction of functional responses to drought and defoliation, and resource costs of the damage-induced leaf trichome density. Our results somewhat challenge the LRM predictions, but further research including field experiments is needed to validate some of the preliminary conclusions drawn. (C) 2008 Elsevier Masson SAS. All rights reserved.
Effects of host plant and maternal feeding experience on population vital rates of a specialized leaf beetle
(2013) Rios, Rodrigo S.; Cardenas, Maritza; Gonzalez, Kely; Cisternas, Monica F.; Guerra, Patricia C.; Loayza, Andrea P.; Gianoli, Ernesto
In herbivorous insects, the interaction between adult preference and progeny performance on specific host plants is modified by maternal feeding experience and host plant quality. Ultimately, changes in the strength of this interaction can affect insect population dynamics. In this study, we hypothesized that adult host plant preference influences progeny performance through a maternal feeding experience x host plant interaction, that is, the effect of adult feeding experience on progeny performance will depend on the host plant. Second, that decoupling of the preference-performance relationship due to host switching results in different population vital rates changing population dynamics. An increase in development time and a decrease in body size of individuals in the alternate host should decrease population growth. We tested these hypotheses using two lines of the tortoise beetle Chelymorpha varians Blanchard fed with two hosts (Convolvulus arvensis and Calystegia sepium). Maternal feeding experience treatments were crossed with host plant species, and the offspring's developing time and adult size were measured. The host plant influence on the beetle's population vital rates was tested using stage-structured matrix population models and life table response experiments. Host plant preference affected offspring body size through a host plant effect that contributed to adaptive life history responses only in the better quality host. C. varians' population growth was positive when fed with either host; comparatively, however, C. sepium had a negative effect on growth by reducing all transition probabilities of the life cycle stages of the beetle. Here, we show that individuals of C. varians prefer and perform differently on distinct hosts and that these patterns influence population vital rates in different ways. When beetles prefer the host plant where their progeny performs best, life history responses and life stage transitions lead to higher population growth; otherwise, growth rate decreases.
Explaining differential herbivory in sun and shade: the case of Aristotelia chilensis saplings
(2010) Guerra, Patricia C.; Becerra, Jose; Gianoli, Ernesto
Differential herbivory in contrasting environments is commonly explained by differences in plant traits. When several plant traits are considered, separate correlation analyses between herbivory and candidate traits are typically conducted. This makes it difficult to discern which trait best explain the herbivory patterns, or to avoid spurious inferences due to correlated characters. Aristotelia chilensis saplings sustain greater herbivory in shaded environments than in open habitats. We measured alkaloids, phenolics, trichomes, leaf thickness and water content in the same plants sampled for herbivory. We conducted a multiple regression analysis to estimate the relationship between herbivory and each plant trait accounting for the effect of correlated traits, thus identifying which trait(s) better explain(s) the differential herbivory on A. chilensis. We also estimated insect abundance in both light environments. Palatability bioassays tested whether leaf consumption by the main herbivore on A. chilensis was consistent with field herbivory patterns. Overall insect abundance was similar in open and shaded environments. While saplings in open environments had thicker leaves, lower leaf water content, and higher concentration of alkaloids and phenolics, no difference in trichome density was detected. The multiple regression analysis showed that leaf thickness was the only trait significantly associated with herbivory. Thicker leaves received less damage by herbivores. Sawfly larvae consumed more leaf tissue when fed on shade leaves. This result is consistent with field herbivory and, together with results of insect abundance, renders unlikely that the differential herbivory in A. chilensis was due to greater herbivory pressure in open habitats.
Extremely Long-Lived Stigmas Allow Extended Cross-Pollination Opportunities in a High Andean Plant
(2011) Torres-Diaz, Cristian; Gomez-Gonzalez, Susana; Stotz, Gisela C.; Torres-Morales, Patricio; Paredes, Brayam; Perez-Millaqueo, Matias; Gianoli, Ernesto
High-elevation ecosystems are traditionally viewed as environments in which predominantly autogamous breeding systems should be selected because of the limited pollinator availability. Chaetanthera renifolia (Asteraceae) is an endemic monocarpic triennial herb restricted to a narrow altitudinal range within the high Andes of central Chile (3300-3500 m a.s.l.), just below the vegetation limit. This species displays one of the larger capitulum within the genus. Under the reproductive assurance hypothesis, and considering its short longevity (monocarpic triennial), an autogamous breeding system and low levels of pollen limitation would be predicted for C. renifolia. In contrast, considering its large floral size, a xenogamous breeding system, and significant levels of pollen limitation could be expected. In addition, the increased pollination probability hypothesis predicts prolonged stigma longevity for high alpine plants. We tested these alternative predictions by performing experimental crossings in the field to establish the breeding system and to measure the magnitude of pollen limitation in two populations of C. renifolia. In addition, we measured the stigma longevity in unpollinated and open pollinated capitula, and pollinator visitation rates in the field. We found low levels of self-compatibility and significant levels of pollen limitation in C. renifolia. Pollinator visitation rates were moderate (0.047-0.079 visits per capitulum per 30 min). Although pollinator visitation rate significantly differed between populations, they were not translated into differences in achene output. Finally, C. renifolia stigma longevity of unpollinated plants was extremely long and significantly higher than that of open pollinated plants (26.3 +/- 2.8 days vs. 10.1 +/- 2.2, respectively), which gives support to the increased pollination probability hypothesis for high-elevation flowering plants. Our results add to a growing number of studies that show that xenogamous breeding systems and mechanisms to increase pollination opportunities can be selected in high-elevation ecosystems.
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.
Genetic variation in the reduction of attractive floral traits of an annual tarweed in response to drought and apical damage
(2016) Gonzáles, Wilfredo L.; Suárez Hernández, Lorena Alejandra; Gianoli, Ernesto
Group size in a gregarious tortoise beetle: patterns of oviposition vs. larval behaviour
(2007) Costa, Juan F.; Cosio, Walter; Gianoli, Ernesto
In laboratory and garden experiments, we tested for the existence of adaptive patterns of oviposition and larval behaviour regarding group size in the gregarious tortoise beetle Chelymorpha varians Blanchard (Coleoptera: Chrysomelidae: Cassidinae) on its host plant Calystegia sepium L. (Convolvulaceae). Specifically, we addressed the following questions: (i) Which is the more frequent egg cluster size? (ii) Does cluster size fully predict larval group size? (iii) Are newborn larvae attracted or repelled to conspecific groupings? and (iv) Which is the group size associated with enhanced larval development and adult mass? We found that the mean cluster size was 21.4 eggs. Egg hatch time was significantly shorter in larger clusters. A regression analysis of larval group size against cluster size showed non-significant results. Thus, original cluster size did not totally determine the larval group size. The mean larval group size was 17.1. Choice tests in an experimental arena showed that larvae clearly preferred leaves of a host plant rather than moistened papers, and that larvae preferred a small group of conspecifics (four larvae per leaf) over larger groups (12 or 20 larvae). Empty leaves of the host plant showed an intermediate level of preference. Development time and beetle performance (adult mass) were affected by larval group size. Larvae in the smallest group (one per leaf) took four more days to attain adulthood than larvae in the larger groups (12 and 20 larvae). Adult C. varians reared in the 12-larvae group were significantly larger than those reared at the other densities. Comparison of patterns across experimental groups, excluding the 12-larvae group, showed a tendency for a greater final mass with slower developmental rate.
Herbivores Modify Selection on Plant Functional Traits in a Temperate Rainforest Understory
(2012) Salgado-Luarte, Cristian; Gianoli, Ernesto
There is limited evidence regarding the adaptive value of plant functional traits in contrasting light environments. It has been suggested that changes in these traits in response to light availability can increase herbivore susceptibility. We tested the adaptive value of plant functional traits linked with carbon gain in contrasting light environments and also evaluated whether herbivores can modify selection on these traits in each light environment. In a temperate rainforest, we examined phenotypic selection on functional traits in seedlings of the pioneer tree Aristotelia chilensis growing in sun (canopy gap) and shade (forest understory) and subjected to either natural herbivory or herbivore exclusion. We found differential selection on functional traits depending on light environment. In sun, there was positive directional selection on photosynthetic rate and relative growth rate (RGR), indicating that selection favors competitive ability in a high-resource environment. Seedlings with high specific leaf area (SLA) and intermediate RGR were selected in shade, suggesting that light capture and conservative resource use are favored in the understory. Herbivores reduced the strength of positive directional selection acting on SLA in shade. We provide the first demonstration that natural herbivory rates can change the strength of selection on plant ecophysiological traits, that is, attributes whose main function is resource uptake. Research addressing the evolution of shade tolerance should incorporate the selective role of herbivores.
Herbivory may modify functional responses to shade in seedlings of a light-demanding tree species
(2011) Salgado-Luarte, Cristian; Gianoli, Ernesto
P>1. The ability to display functional responses to shading, i.e. phenotypic changes that enhance plant performance in low light, is fundamental for plant success in forest communities. Herbivory may constrain plant functional responses to shading and this could explain the often observed lower plant tolerance of herbivore damage in the shade.

Browsing by Author "Gianoli, Ernesto"

Results Per Page

Sort Options