Epiphytic Bromeliads Research Articles

Morphophysiological screening of potential organisms for biomonitoring nitrogen deposition

• Local species of different functional groups can be screened in regions of interest. • This proof-of-concept focused on the highly polluted megalopolis of Mexico City. • The moss Braunia secunda is a potential biomonitor of N deposition. • The moss Thuidium delicatulum experienced damage under all N treatments. • Neither Tillandsia had visual nor physiological response to simulated N deposition. The intensification of different anthropic activities has led to a doubling of the emitted reactive nitrogen species since the second half of the XX century, resulting in the increase of nitrogen deposition. This poses a major threat to global biodiversity. However, in developing countries the monitoring of atmospheric deposition has shown to be difficult. For these reasons, the aim of this study was to assess, by means of a greenhouse dose-response experiment, the biomonitoring potential of two mosses, Braunia secunda and Thuidium delicatulum , and two epiphytic bromeliads, Tillandsia recurvata and Tillandsia usneoides , which are widely distributed in Latin America. A significant increase of the phosphomonoesterase activity was observed for the mosses, particularly under a High-nitrogen treatment, a parameter that decreased for the bromeliads. In turn, the nitrate reductase activity decreased over the course of the experiment for the mosses, but it remained almost unchanged for both tillandsias. While the nitrogen content for the mosses increased, it fluctuated for the bromeliads. Braunia secunda became greener under the Low-nitrogen than under the other treatments, while the coloration for T. delicatulum turned to brown under all treatments. The tillandsias remained visually unchanged under all treatments. The mosses had a clear response to the simulated nitrogen deposition, with B. secunda being more tolerant than T. delicatulum . Neither tillandsia presented a clear response to the treatments. Thus, the moss B. secunda is a very suitable species for biomonitoring nitrogen deposition, while the other species evaluated were deemed unsuitable.

Complex indirect effects of epiphytic bromeliads on the invertebrate food webs of their support tree

AbstractEcosystem engineers are species that affect others through the provision of habitat rather than consumptive resources. The extent to which ecosystem engineers can indirectly affect entire food webs, however, is poorly understood. Epiphytic tank bromeliads (Bromeliaceae) are ecosystem engineers that are common throughout the Neotropics, and are associated with a variety of predatory arthropods. Here, we examine if bromeliads, by increasing predator densities, indirectly benefit their support tree through reduction in herbivorous insects and leaf damage. We observed and manipulated bromeliad densities in Costa Rican orange orchards, and measured impacts on leaf damage and arboreal and bromeliad invertebrate communities in two different seasons. Our results show that bromeliads are associated with predatory and herbivorous invertebrates but not leaf damage. Bromeliads were correlated with increased densities of their associated predators, especially ants and hunting spiders, but we could not confirm a causal link. Associations with bromeliads changed over time, with seasonal shifts interfering with responses to our manipulations. Bromeliads had a reduced association with predators in the dry season. Moreover, a null association between bromeliads and herbivorous invertebrates in the dry season unexpectedly became positive in the wet season. In summary, we have only limited evidence that bromeliads indirectly promote the top‐down control of arboreal herbivores; instead, our manipulations suggest that bromeliads increase herbivore densities in the wet season. This research suggests that although bromeliads may act as ecosystem engineers, indirectly influencing the invertebrate food web on support trees, their effects are trophically complex and seasonally dependent.Abstract in Spanish is available with online material.

Changes in rainfall level and litter stoichiometry affect aquatic community and ecosystem processes in bromeliad phytotelmata

Abstract Both N deposition and changes in precipitation amount are important components of global change and affect aquatic ecosystem functioning by altering the detrital quality and detrital processing rates by macroinvertebrates and microorganisms. Changes in precipitation pattern can also modify the physical structure of the ecosystem, determining habitat availability for aquatic organisms. Although these drivers can individually affect ecosystem structure and functioning, their interactive effects are poorly understood. To better understand the combined effects of detritus quality and precipitation regime on the structure and function of aquatic ecosystems we manipulated litter quality, by modifying N:P stoichiometry and rainfall amount on tropical natural aquatic microcosms (water‐holding epiphytic bromeliads). We performed an orthogonal manipulation of litter N:P ratio (natural N:P and high N:P) and rainfall levels (current level and predicted 40% increase for south‐eastern Brazil) Changes in litter quality affected the abundance of the aquatic organisms inhabiting bromeliads, including algae and bacteria. However, changes in litter quality combined with changes in precipitation levels affected only one group of macroinvertebrates, the Naididae worms (Oligochaeta) an important group of detritivores in the bromeliad systems. These combined drivers also affected the decomposition of organic matter by changing coloured organic matter concentrations, fine particulate matter biomass, and concentrations in bromeliad tanks. The concentration in bromeliad water was positively related with Naididae abundance, suggesting that these worms can act as ecosystem engineers by boosting N cycling. In both N:P treatments we observed a 50% decrease in N flux from litter to bromeliad leaves due to increases in nutrient leaching from the tanks caused by rainfall. The combined effects of litter quality and changes in precipitation regimes altered the decomposition process and nutrient cycling in tank bromeliads, probably through changes in the abundance of some keystone species (e.g. Naididae). Aquatic macroinvertebrate community structure remained similar after manipulating precipitation, despite changes in the abundance of some species. Although some microorganisms were washed out of the system, their abundance inside the bromeliads remained stable. We conclude that the abundance of individuals belonging to aquatic communities in bromeliad phytotelmata are generally stable and resistant to changes in rainfall levels, but are sensitive to changes in litter quality. This experiment showed that the interactive effects of increased precipitation and N concentrations differed from the effects of either factor alone. As responses to changes in these factors were complex rather than additive, caution is required in predicting the outcomes of changes in both factors in freshwater ecosystems.

Involvement of aquaporins on nitrogen-acquisition strategies of juvenile and adult plants of an epiphytic tank-forming bromeliad.

Depending on the N source and plant ontogenetic state, the epiphytic tank-forming bromeliad Vriesea gigantea can modulate aquaporin expression to maximize the absorption of the most available nitrogen source. Epiphytic bromeliads frequently present a structure formed by the overlapping of leaf bases where water and nutrients can be accumulated and absorbed, called tank. However, this structure is not present during the juvenile ontogenetic phase, leading to differences in nutrient acquisition strategies. Recent studies have shown a high capacity of the bromeliad Vriesea gigantea, an epiphytic tank-forming bromeliad, to absorb urea by their leaves. Since plant aquaporins can facilitate the diffusion of urea through the membranes, we cloned three foliar aquaporin genes, VgPIP1;1, VgPIP1;2 and VgTIP2;1 from V. gigantea plants. Through functional studies, we observed that besides water, VgTIP2;1 was capable of transporting urea while VgPIP1;2 may facilitate ammonium/ammonia diffusion. Moreover, aiming at identifying urea and ammonium-induced changes in aquaporin expression in leaves of juvenile and adult-tank plants, we showed that VgPIP1;1 and VgPIP1;2 transcripts were up-regulated in response to either urea or ammonium only in juvenile plants, while VgTIP2;1 was up-regulated in response to urea only in adult-tank plants. Thereby, an ontogenetic shift from juvenile to adult-tank-forming-plant appears to occur with metabolic changes regarding nitrogen metabolism regulation. Investigating urea metabolism in wild species that naturally cope with organic N sources, such as V. gigantea, may provide the knowledge to modify nitrogen use efficiency of crop plants.

Water and nutrient uptake capacity of leaf-absorbing trichomes vs. roots in epiphytic tank bromeliads

The water and nutrient uptake mechanisms used by vascular epiphytes have been the subject of a few studies. While leaf absorbing trichomes (LATs) are the main organ involved in resource uptake by bromeliads, little attention has been paid to the absorbing role of epiphytic bromeliad roots. This study investigates the water and nutrient uptake capacity of LATs vs. roots in two epiphytic tank bromeliads Aechmea aquilega and Lutheria splendens. The tank and/or the roots of bromeliads were watered, or not watered at all, in different treatments. We show that LATs and roots have different functions in resource uptake in the two species, which we mainly attributed to dissimilarities in carbon acquisition and growth traits (e.g., photosynthesis, relative growth rate, non-structural carbohydrates, malate), to water relation traits (e.g., water and osmotic potentials, relative water content, hydrenchyma thickness) and nutrient uptake (e.g., 15N-labelling). While the roots of A. aquilega did contribute to water and nutrient uptake, the roots of L. splendens were less important than the role played by the LATs in resource uptake. We also provide evidenced for a synergistic effect of combined watering of tank and root in the Bromelioideae species. These results call for a more complex interpretation of LATs vs. roots in resource uptake in bromeliads.

How significant are endophytic fungi in bromeliad seeds and seedlings? Effects on germination, survival and performance of two epiphytic plant species

In bromeliads, nothing is known about the associations fungi form with seeds and seedling roots. We investigated whether fungal associations occur in the seeds and seedling roots of two epiphytic Aechmea species, and we explored whether substrate and fungal associations contribute to seed germination, and seedling survival and performance after the first month of growth. We found a total of 21 genera and 77 species of endophytic fungi in the seeds and seedlings for both Aechmea species by Illumina MiSeq sequencing. The fungal associations in seeds were found in the majority of corresponding seedlings, suggesting that fungi are transmitted vertically. Substrate quality modulated the germination and growth of seedlings, and beneficial endophytic fungi were not particularly crucial for germination but contributed positively to survival and growth. Overall, this study provides the first evidence of an endophytic fungal community in both the seeds and seedlings of two epiphytic bromeliads species that subsequently benefit plant growth.

Vertebrate florivory of vascular epiphytes: the case of a bromeliad

The avoidance of vertebrate herbivory is thought to be one of the possible drivers for the evolution of epiphytism. Scarce literature suggests that epiphyte herbivory is mainly related to insect attack on reproductive structures. In a pine-oak forest we observed almost all inflorescences of an epiphytic bromeliad (Tillandsia carlos-hankii) with signs of florivory; the degree of damage suggested that vertebrate herbivores could be involved. To assess the intensity of vertebrate florivory damage we recorded the percentage of damaged individuals in a 500 m2 plots during two flowering seasons. To identify possible vertebrate herbivores, we installed 20 mixed capture stations, 10 photo-traps focused on bromeliads and analyzed stomach contents of captured vertebrates. Florivory was observed on 62% of individuals during the first flowering season and 77% on the second; and average one individual lost 41% of reproductive structures. Vertebrates associated with florivory were a bird, Icterus bullockii (Aves, Passeriformes, Icteridae), a squirrel Sciurus aureogaster (Mammalia, Rodentia, Sciuridae), and mice, Peromyscus gratus, P. levipes and P. aztecus (Mammalia, Rodentia, Cricetidae). Our results suggest that vascular epiphytes are used as opportunistic resources for small vertebrates during seasons when preferred resources are scarce.

Bromeliaceae subfamilies show divergent trends of genome size evolution

Genome size is known to vary widely across plants. Yet, the evolutionary drivers and consequences of genome size variation across organisms are far from understood. We investigated genome size variation and evolution in two major subfamilies of the Neotropical family Bromeliaceae by determining new genome size values for 83 species, testing phylogenetic signal in genome size variation, and assessing the fit to different evolutionary models. For a subset of epiphytic bromeliad species, we also evaluated the relationship of genome size with thermal traits and relative growth rate (RGR), respectively. Genome size variation in Bromelioideae appears to be evolutionary conserved, while genome size among Tillandsioideae varies considerably, not just due to polyploidy but arguably also due to environmental factors. The subfamilies show fundamental differences in genome size and RGR: Bromelioideae have, on average, lower genome sizes than Tillandsioideae and at the same time exhibit higher RGR. We attribute this to different resource use strategies in the subfamilies. Analyses among subfamilies, however, revealed unexpected positive relationships between RGR and genome size, which might be explained by the nutrient regime during cultivation. Future research should test whether there is indeed a trade-off between genome size and growth efficiency as a function of nutrient supply.

Identification of areas of endemism in the Mexican cloud forests based on the distribution of endemic epiphytic bromeliads and orchids

To identify areas of endemism (AEs) in the Mexican cloud forests based on the distribution of endemic epiphytic bromeliads and orchids species and to propose a hypothesis about the current biogeographical relationship of the Mexican cloud forests. The AEs were identified using 1007 records corresponding to 205 species and the endemicity analysis as is implemented in the ndm/vndm programs. To obtain the consensus areas a strict consensus analysis was carried out considering 60% of shared species as the lower limit; those that presented an Endemicity Index ≥ 3.0 were recognized as AEs. A parsimony analysis of endemicity was performed with winclada/nona programs to infer their biogeographical relationships. Five AEs were recognized: 1) Western Mexico (supported by six species), 2) Southern Mexico (eight species), 3) Northern Gulf of Mexico, and 4) Central Gulf of Mexico (with nine species each), and 5) Northern Oaxaca (four species). The spatial homology hypothesis suggests that the areas of endemism from the Pacific Ocean Slope and from the Gulf of Mexico Slope has a different evolutionary history. Each AEs has a different species composition; the greatest species diversity is presented in the Gulf of Mexico slope AEs, while the greatest diversity of exclusive species is presented in the Pacific Ocean slope AEs. There is no a spatial homology hypothesis between the AEs of the Gulf of Mexico and the AEs of the Pacific Ocean, therefore, our results do not support the hypothesis of a cloud forest with continuous distribution in the past. The divergence times of the bromeliads and orchids and ecological succession theory could explain our results.

External water transport is more important than vascular transport in the extreme atmospheric epiphyte Tillandsia usneoides (Spanish moss).

Most epiphytic bromeliads, especially those in the genus Tillandsia, lack functional roots and rely on the absorption of water and nutrients by large, multicellular trichomes on the epidermal surfaces of leaves and stems. Another important function of these structures is the spread of water over the epidermal surface by capillary action between trichome "wings" and epidermal surface. Although critical for the ultimate absorption by these plants, understanding of this function of trichomes is primarily based on light microscope observations. To better understand this phenomenon, the distribution of water was followed by its attenuation of cold neutrons following application of H2 O to the cut end of Tillandsia usneoides shoots. Experiments confirmed the spread of added water on the external surfaces of this "atmospheric" epiphyte. In a morphologically and physiologically similar plant lacking epidermal trichomes, water added to the cut end of a shoot clearly moved via its internal xylem and not on its epidermis. Thus, in T.usneoides, water moves primarily by capillarity among the overlapping trichomes forming a dense indumentum on shoot surfaces, while internal vascular water movement is less likely. T.usneoides, occupying xeric microhabitats, benefits from reduction of water losses by low-shoot xylem hydraulic conductivities.

IN VITRO PROPAGATION OF VRIESEA INCURVATA: CONSERVATION OF A BROMELIAD ENDEMIC TO THE ATLANTIC FOREST

Vriesea incurvata is an epiphytic bromeliad of the Atlantic Forest with ornamental attributes that encourage extractivism. This study assessed the influence of sucrose (10, 30 and 60 g L-1) on the survival and development of V. incurvata plantlets cultivated for 180 days on MS medium and acclimatizated for 150 days under controlled conditions. Survival of 100% was recorded in all in vitro treatments. Sucrose at concentration of 60 g L-1 provided highest length of the aerial portion and of the longest root, greatest number of leaves and roots, highest fresh mass and lowest contents of chlorophylls and carotenoids. The higher sucrose concentration also positively influenced the development of plantlets ex vitro, allowing for increased averages for the parameters assessed. The results indicate micropropagation as an alternative by which V. incurvata plantlets may be provided for commercial means, reducing the extractivism from natural populations, or for reintroduction into their natural habitat.

Dew Can Prolong Photosynthesis and Water Status During Drought in Some Epiphytic Bromeliads From a Seasonally Dry Tropical Forest

Dew can represent an alternate water source in epiphytic bromeliads. However, the physiological relevance of dew to withstand the dry season, within seasonal forests, is not fully understood. To study the effect of dew deposition in the physiological response of four Tillandsia species with contrasting morphologies, we performed an experiment in the tropical dry deciduous forest of Dzibilchaltún, Mexico, during the transition from the wet to the dry season. Half of the individuals were covered every night with a plastic tarp to prevent dew deposition. Environmental variables were monitored, and physiological variables (relative water content, leaf succulence, nocturnal tissue acidification and electron transport rate) were measured at the beginning and end of the experiment. We found that throughout the drought, there was consistent nighttime dew formation for >4 h. Both the time the leaves spent at a temperature below dew point of the air and the effect on water and carbon metabolism was species -specific, as evidenced by the comparison among the exposed and covered (dew -deprived) plants. Tillandsia elongata and Tillandsia brachycaulos had longer times of dew formation and showed higher water content at the end of the experiment when exposed to dew, the latter species also had a significant effect of dew on nocturnal acidity. In contrast, neither Tillandsia yucatana nor Tillandsia fasciculata seemed to be using dew as a relevant source of water during the dry period. We discuss the species’ morphoanatomical traits that may be related to the differences in dew formation and use.

Daily Evapotranspiration of Guzmania ‘Irene’ and Vriesea ‘Carly’ Bromeliads Produced in a Shaded Greenhouse

Bromeliads are important ornamental foliage plants, but until now, their daily water use during production was unknown. Using a canopy closure model developed for container-grown woody ornamental plants, in this study we investigated actual evapotranspiration (ETA) of Guzmania ‘Irene’ and Vriesea ‘Carly’ from tissue-cultured liners grown in 15-cm containers to marketable sizes in a shaded greenhouse. The mean daily ETA of Guzmania ‘Irene’ ranged from 4.02 to 66.35 mL per plant, and the mean cumulative ETA was 16.66 L over a 95-week production period. The mean daily ETA of Vriesea ‘Carly’ varied from 3.98 to 59.89 mL per plant, and the mean cumulative ETA was 15.52 L over the same production period as the Guzmania cultivar. The best-fit models for predicting daily ETA of the two bromeliads were developed, which had correlation coefficients (r2) of 0.79 for Guzmania ‘Irene’ and 0.68 for Vriesea ‘Carly’. The success in the model of ETA for both bromeliads suggested that the canopy closure model was equally applicable to container-grown ornamental foliage plants produced in greenhouse conditions. The daily ETA and cumulative ETA values represent research-based information on water requirements, and, when applied, could improve irrigation practices in bromeliad production. This study also showed that roots per se of the two epiphytic bromeliads were able to absorb water and nutrients from a peat-based container substrate and support their complete life cycles.

Ciliate species from tank-less bromeliads in a dry tropical forest and their geographical distribution in the Neotropics.

The study of ciliate diversity in tropical environments remains scarce. In Neotropical forests, bromeliads are a common component of the vascular flora; bromeliads with tank morphology intercept rain water and detritus, resulting in the formation of a phytotelm, where heterotrophic protist communities like ciliates can establish. However, it is not known if ciliates inhabit tank-less bromeliads. For this reason, the goal of the present study was to investigate if ciliates can establish between the leaf axils of five terrestrial and epiphytic tank-less bromeliad species in a dry tropical forest in west Mexico. We collected samples of rain water and detritus from the leaf axils during the humid season of years 2015 and 2016. For ciliate taxonomical identification, we used optical microscopy, in vivo observation, and silver impregnation techniques. To summarize information about geographical distribution of ciliates identified at species level in the Neotropics, we provided their records from previous works, at country level with locality and georeferenciation. We recorded 27 taxa of ciliates, where the class Oligohymenophorea contained the largest richness of taxa. Drepanomonas revoluta, Leptopharynx bromeliophilus, and Tetrahymena sp. were recorded from all the species of bromeliads. Bromelia karatas was the species that hosted the largest number of ciliate taxa (22). Our results indicated that Glaucomides bromelicola, Gonostomum bromelicola, Leptopharynx bromelicola and L. bromeliophilus, species which are considered endemic to tank bromeliads, can also inhabit tank-less bromeliads. We provided previous records of 19 ciliate species from eleven countries within the Neotropical region, and Bromeliothrix metopoides was the species most frequently recorded in Neotropical countries (9). Therefore, tank-less bromeliads can constitute a temporal habitat for ciliates, and function as cysts reservoirs in environments with a pronounced seasonality like dry tropical forests.

Nectar ecology of the endemic epiphytic hummingbird-pollinated bromeliad Vriesea altodaserrae: secretion dynamics and pollinator visitation pattern

ABSTRACT Hummingbirds are the main pollinators of most bromeliad species, whose nectar traits usually respond to the selective pressures imposed by pollinators. Considering the specialization of hummingbird-pollinated bromeliads, we expect a close relationship between nectar ecophysiology and the needs of the main pollinators. In this sense, we studied the nectar ecology of the endemic epiphytic bromeliad Vriesea altodaserrae by assessing its nectar traits to address the following questions: i) do flowers respond to successive experimental removals of nectar? ii) is hummingbird visitation frequency related to nectar secretion pattern? We found that V. altodaserrae depended completely on hummingbirds for sexual reproduction, and nectar composition was consistent with that of most hummingbird-pollinated species. Most of the nectar was secreted at bud stage and, if not removed, flowers reabsorb it at the end of their lifespan. Total nectar production did not change after successive removals, and nectar secretion rhythm did not affect the frequency of hummingbird visits. Vriesea altodaserrae was visited by two-thirds of the hummingbird species recorded at the study site, but especially by those of Trochilinae subfamily, suggesting specialization for this group of hummingbirds and highlighting the importance this endemic bromeliad as a keystone species in areas of highland Atlantic forest.

Nitrogen efficiency indexes for evaluating nitrogen uptake and use in ornamental bromeliad’s root system and tank

Abstract: The objective of this work was to evaluate if nitrogen use efficiency (NUE) indexes can elucidate functional differences in nutrient uptake between the root system and tank of epiphytic bromeliads. The bromeliads Guzmania lingulata and Vriesea 'Harmony' received fertilizers in their tanks or through their roots using modified Hoagland & Arnon solution, with 0.00, 2.62, or 5.34 mmol L-1 nitrogen, as urea. After 90 days, nitrogen contents in leaves and plant biomass were evaluated, and NUE indexes were calculated. Guzmania lingulata and V. 'Harmony' fertilized in their tanks with 5.34 mmol L-1 had the highest averages of nitrogen uptake efficiency and recovery efficiency; those fertilized with 2.62 mmol L-1 through their roots showed the highest averages of NUE, nitrogen utilization efficiency, nitrogen physiological efficiency, and biomass conversion efficiency. The NUE indexes, besides being an effective tool to assess the nutritional status of ornamental bromeliads, reveal that the root system of epiphytic bromeliads is functional for nitrogen uptake and use.

Reproductive traits and floral visitors of Aechmea distichantha plants growing in different habitats of a South American xerophytic forest

Abstract Aechmea distichantha, a widely-distributed facultative epiphytic bromeliad species, is present from rainforests to xerophytic forests. At its southernmost distribution (Humid Chaco) it grows in the understory and forest edges. This animal-pollinated bromeliad shows high phenotypic plasticity on its vegetative traits, but there is no information about plasticity on its reproductive traits. Infructescences from shade plants were heavier, had longer rachis, more spikelets, higher number of fruits/spikelet and higher number of seeds/fruit than those from sun plants, but they presented similar number of open flowers. The number of visitation events was similar in both habitats, but more flowers were visited in the sun than in the shade. Flowers were visited by seven species (six insects and one hummingbird). In the sun, the carpenter bee was the most frequent visitor and visited almost all flowers, whereas in the shade different species of visitors attained similar proportion of visits and number of visited flowers. Despite visitation events were similar in both habitats, plants growing in the shade set more seeds/fruit than plants growing in the sun. The higher proportion of visits accomplished by carpenter bees compared to hummingbirds is probably a consequence of the climatic conditions in the austral location of these populations.

Epiphytic bromeliads in a changing world: the effect of elevated CO2 and varying water supply on growth and nutrient relations.

Global climate change is likely to impact all plant life. Vascular epiphytes represent a life form that may be affected more than any other by possible changes in precipitation leading to water shortage, but negative effects of drought may be mitigated through increasing levels of atmospheric CO2 . We studied the response of three epiphytic Aechmea species to different CO2 and watering levels in a full-factorial climate chamber study over 100days. All species use crassulacean acid metabolism (CAM). Response variables were relative growth rate (RGR), nocturnal acidification and foliar nutrient levels (N, P, K, Mg). Both elevated CO2 and increased water supply stimulated RGR, but the interaction of the two factors was not significant. Nocturnal acidification was not affected by these factors, indicating that the increase in growth in these CAM species was due to higher assimilation in the light. Mass-based foliar nutrient contents were consistently lower under elevated CO2 , but most differences disappeared when expressed on an area basis. Compared to previous studies with epiphytes, in which doubling of CO2 increased RGR, on average, by only 14%, these Aechmea species showed a relatively strong growth stimulation of up to +61%. Consistent with earlier findings with other bromeliads, elevated CO2 did not mitigate the effect of water shortage.

Distribution of Costa Rican epiphytic bromeliads and the Holdridge Life Zone System

Detailed distribution maps for the major bromeliad genera native to Costa Rica were prepared bases on the collections in the three largest herbaria of the country and on citations from the literature. Most records are from the montane habitats, probably reflecting the frequent need for moisture by these plants. Vriesea ans Guzmania have been collected mostly in moist lowland habitats. In 1975, Burt-Utley and Utley had hypothesized that the Holdridge Life Zone System should fit the distribution of epiphytic bromeliads because soil (a factor not considered in the System) is not important in their occurrence. However, on average, species were absent in about half of the Life Zones where they were expected to occur according to the Holdridge classification. It is hypothesized that the System failed because epiphytic bromeliad distribution reflects factor interactions rather than humidity, light or temperature individually.

Nectar ecology of the endemic epiphytic hummingbird-pollinated bromeliad Vriesea altodaserrae: secretion dynamics and pollinator visitation pattern

ABSTRACT Hummingbirds are the main pollinators of most bromeliad species, whose nectar traits usually respond to the selective pressures imposed by pollinators. Considering the specialization of hummingbird-pollinated bromeliads, we expect a close relationship between nectar ecophysiology and the needs of the main pollinators. In this sense, we studied the nectar ecology of the endemic epiphytic bromeliad Vriesea altodaserrae by assessing its nectar traits to address the following questions: i) do flowers respond to successive experimental removals of nectar? ii) is hummingbird visitation frequency related to nectar secretion pattern? We found that V. altodaserrae depended completely on hummingbirds for sexual reproduction, and nectar composition was consistent with that of most hummingbird-pollinated species. Most of the nectar was secreted at bud stage and, if not removed, flowers reabsorb it at the end of their lifespan. Total nectar production did not change after successive removals, and nectar secretion rhythm did not affect the frequency of hummingbird visits. Vriesea altodaserrae was visited by two-thirds of the hummingbird species recorded at the study site, but especially by those of Trochilinae subfamily, suggesting specialization for this group of hummingbirds and highlighting the importance this endemic bromeliad as a keystone species in areas of highland Atlantic forest.