Scielo RSS <![CDATA[Acta Botanica Brasilica]]> vol. 31 num. 4 lang. en <![CDATA[SciELO Logo]]> <![CDATA[Phylogenetic community structure reveals differences in plant community assembly of an oligotrophic white-sand ecosystem from the Brazilian Atlantic Forest]]> ABSTRACT Mussununga, an oligotrophic sandy savanna ecosystem, comprises distinct physiognomies along fire, water and nutrient availability gradients. Grasslands and woodlands are constrained at the opposite poles of these gradients, with grasslands occurring in areas with poorer soils and higher levels of both water-stress and fire intensity. According to the stress-dominance hypothesis, one might expect the importance of competition for community assembly to increase from grasslands to woodlands. Assuming conservation of ecological niches within evolutionary lineages, this should increase phylogenetic overdispersion from grasslands towards woodlands. To test this, we calculated phylogenetic diversity and community structure using different null models as well as the phylogenetic signal of life form as a proxy of niche space. All indices indicate phylogenetic clustering for grasslands and phylogenetic overdispersion for woodlands. Considering that most life-forms showed a significant phylogenetic signal, findings indicate that competition and further density dependent factors may play a larger role in community assembly of physiognomies in less harsh positions along the gradient, while environmental filtering dominates the harsher positions. Our results indicate that the entire gradient should receive conservation priority in order to guarantee the effective conservation of this endangered ecosystem, including its species richness and ecological processes such as community assembly. <![CDATA[Survival and growth of tree seedlings as a function of seed size in a gallery forest under restoration]]> ABSTRACT Seed size is commonly related to higher rates of emergence and survival, and biomass of seedlings when introduced by direct seeding. However, few studies have evaluated whether this relationship persists when species are reintroduced as seedlings or if this effect persists after seed reserves decline. This study evaluated the effect of seed size (mass) on the probability of survival and growth of seedlings of nine native tree species introduced into a pasture area, which was originally a gallery forest in the state of São Paulo in Southeastern Brazil. The experiment occurred over the course of 24 months, in which was divided into three separate time intervals: 14 to 61 days, 61 days to 12 months, and 12 to 24 months. Seedling survival in the field was high for all three time-intervals. Seed mass positively influenced the probability of seedling survival throughout all three time-intervals after planting, but the intensity of this effect decreased with time. Species with smaller seeds exhibited higher relative growth rates (height), but only until the end of the first year. Our results suggest that seed mass is a functional trait that can predict the probability of the establishment of individual trees during forest restoration. <![CDATA[Management techniques for the control of <em>Melinis minutiflora</em> P. Beauv. (molasses grass): ten years of research on an invasive grass species in the Brazilian Cerrado]]> ABSTRACT The invasion of exotic species is considered to be a major threat to the preservation of biodiversity. In the Parque Nacional de Brasília (National Park of Brasília), the invasive Melinis minutiflora (molasses grass) occupies more than 10 % of the area of the park. The present, long-term, study compared two treatments of exposure to molasses grass: 1) fire and 2) integrated management (fire + herbicide sprays + manual removal). The aerial biomass of molasses grass in the experimental area initially represented ca. 55 % of the total aerial biomass, a percentage that apparently did not influence native plant species richness at this site. Fire alone was not sufficient to control molasses grass, which attained its pre-treatment biomass values after two years. Integrated management reduced, and maintained, biomass to less than 1 % of its original value after ten years, and maintained this level throughout the study, demonstrating that it is a promising strategy for the recovery of areas invaded by molasses grass in the Cerrado. However, because of the recolonization by molasses grass, long-term monitoring efforts are targeting outbreaks, which would require immediate intervention in order to maintain the native biological diversity of the region. <![CDATA[Effects of salinity on the physiology of the red macroalga, <em>Acanthophora spicifera</em> (Rhodophyta, Ceramiales)]]> ABSTRACT Salinity is an important abiotic factor since it is responsible for the local and/or regional distribution of algae. In coastal regions, salinity changes with prevailing winds, precipitation and tide, and particularly in extreme intertidal conditions. Acanthophora spicifera is a red seaweed that occurs in the supratidal region in which changes in abiotic conditions occur frequently. This study evaluated the effects of salinity on the metabolism and morphology of A. spicifera. Algae were acclimatized under culture conditions with sterilized seawater for seven days. Experiments used different salinities (15 to 50 psu) for seven days, followed by metabolic analyses. This study demonstrates that extreme salinities affect physiological parameters of A. spicifera, such as decrease in growth rate, as well as morphological parameters and concentrations of secondary metabolites. Acanthophora spicifera exhibited high tolerance to 25 to 40 psu, with little change in physiology, which favors the occurrence of this species in diverse environments. However, 15, 20, 45 and 50 psu were the most damaging and led to loss of biomass, depigmentation of apices, and the highest concentrations of antioxidant metabolites. The 50 psu treatment caused the greatest changes in general, greatly reducing a biomass and chlorophyll content, and facilitating the presence of endophytes. <![CDATA[Host-exclusivity and host-recurrence by wood decay fungi (Basidiomycota - Agaricomycetes) in Brazilian mangroves]]> ABSTRACT This study aimed to investigate for the first time the ecological interactions between species of Agaricomycetes and their host plants in Brazilian mangroves. Thirty-two field trips were undertaken to four mangroves in the state of Pernambuco, Brazil, from April 2009 to March 2010. One 250 x 40 m stand was delimited in each mangrove and six categories of substrates were artificially established: living Avicennia schaueriana (LA), dead A. schaueriana (DA), living Rhizophora mangle (LR), dead R. mangle (DR), living Laguncularia racemosa (LL) and dead L. racemosa (DL). Thirty-three species of Agaricomycetes were collected, 13 of which had more than five reports and so were used in statistical analyses. Twelve species showed significant values for fungal-plant interaction: one of them was host-exclusive in DR, while five were host-recurrent on A. schauerianna; six occurred more in dead substrates, regardless the host species. Overall, the results were as expected for environments with low plant species richness, and where specificity, exclusivity and/or recurrence are more easily seen. However, to properly evaluate these relationships, mangrove ecosystems cannot be considered homogeneous since they can possess different plant communities, and thus different types of fungal-plant interactions. <![CDATA[Assessing the spatial variation of functional diversity estimates based on dendrograms in phytoplankton communities]]> ABSTRACT Variation in phytoplankton functional diversity is partioned and mapped using several indices and linkage methods based on dendrograms. The relationships between diversity metrics and major environmental predictors, including zooplankton density, were assessed in 29 phytoplankton communities of floodplain lakes distributed along the Middle Araguaia River in central Brazil. The dendrogram-based functional diversity indices were Functional Group Richness, Functional Diversity, Mean Pairwise Distance and Mean Nearest Taxon Distance, whereas seven different hierarchical agglomerative linkage methods we used. The performance of indices were compared using ANOVA and their spatial variation in response to major environmental predictors evaluated. The results indicate that variation in functional diversity values is primarily a product of the type of index chosen. This variation was statistically significant in 90 % of the floodplain lakes studied; however, a spatial pattern of variation in index values along the river was not detected. Furthermore, environmental constraints, including zooplankton density, were weak predictors of functional diversity indices. Therefore, the mathematical characteristics of indices are of primary importance in explaining variation among functional diversity values. <![CDATA[Antiherbivory defense mechanisms along an environmental gradient in <em>restinga</em>]]> ABSTRACT Plant-herbivore interactions have directed the evolution of defense mechanisms in plants, which can vary intraspecifically according to environmental quality. This study evaluated variation in the production of antiherbivory defenses in plant species distributed along an environmental gradient of restinga. The study was performed in Parque Estadual Acaraí, state of Santa Catarina, Brazil. Three species of four plant formations with different abiotic conditions were selected for study. Specific leaf area; water, nitrogen and carbon content; and presence of phenols, tannins, lignin and alkaloids, were evaluated in leaves of ten plants per species per plant formation. The results indicated that Symphyopappus casarettoi possesses Low Nutritional Quality Syndrome, characterized by low specific leaf area, presence of secondary metabolites and low nitrogen content. Dodonaea viscosa and Varronia curassavica possess Nutrition and Defense Syndrome, characterized by a balance between nutritional quality (high nitrogen content and lower C:N ratio) and protection (greater thickness of leaves and higher density of trichomes). The results did not confirm the Resource Availability Hypothesis. The absence of a pattern in antiherbivory response due to the environmental gradient may indicate that the investment in defense by plants is not unidirectional and that certain morpho-anatomical attributes are typically related to conservation of resources. <![CDATA[Pollen morphology of <em>Waltheria</em> L. (Malvaceae-Byttnerioideae) from Bahia, Brazil]]> ABSTRACT Waltheria encompasses about 60 species distributed in Brazil and Mexico. To improve the palynology of the genus, we analyzed 14 species occurring in the Brazilian State of Bahia. Pollen grains were acetolyzed and examined using light microscopy and scanning electron microscopy. Non-acetolyzed pollen grains were viewed by transmission electron microscopy. The results revealed two general pollen types based on exine ornamentation, such as reticulate and echinate, which are distinct with regard to (1) size and shape, (2) apertural type and number, (3) relative length of ectoapertures, and (4) thickening of the nexine compared to the sexine. An ultrastructural analysis of the pollen wall revealed a continuous foot layer and a compact and discontinuous endexine in most cases. The sexine consisted of heterogeneous columellae, which support a perforated semitectum (echinate type) or the semitectum was composed of perforations and muri-shaped thickening (reticulate type). These results confirm a high degree of pollen dimorphism in Waltheria associated with heterostyly. <![CDATA[Typifications in <em>Passiflora</em> L. (Passifloraceae) described by Frei José Mariano da Conceição Vellozo]]> ABSTRACT This work presents 19 lectotypifications and one epitype for the genus Passiflora (Passifloraceae sensu stricto) described by Frei José Mariano da Conceição Vellozo in Flora Fluminensis. The original illustrations are designated as lectotypes. Passiflora obtusa is here proposed to be a synonym of P. porophylla. <![CDATA[A synopsis of <em>Galianthe</em> (Rubiaceae) in Rio Grande do Sul, Southern Brazil, and a new endemic species from Serra Geral]]> ABSTRACT Thirteen species of the genus Galianthe have been recorded for state of Rio Grande do Sul, Brazil. The species are distributed among seven biomes, one of which contains all thirteen taxa-Subtropical Seasonal Forest. Herein a new endemic species, G. riograndensis J. Florentín &amp; E.L. Cabral, is described, illustrated and differentiated from all other species of the genus by having 3-4 verticillate leaves and a long bifid style. In addition, the pollen grain morphology and the seed micromorphology of the new species are described and illustrated, and the conservation status assessed according to IUCN criteria. Moreover, G. chodatiana is recorded for the first time from the state, and a lectotype for G. equisetoides is designated. Most of the species of Galianthe are described and illustrated with detailed photos of living specimens. A taxonomic key for species identification, as well as comments on distribution, overall phenology and habitat, are also presented. The distribution of the new species is discussed in the context of the biogeographic region of the state, and maps and a table of species by biome are also provided. <![CDATA[Relationship between seed moisture content and acquisition of impermeability in <em>Nelumbo nucifera</em> (Nelumbonaceae)]]> ABSTRACT Seeds of Nelumbo nucifera do not imbibe water, and thus have physical dormancy (PY). However, a proportion of seeds are permeable to water, and so we hypothesized that variation in moisture content is a reason for the development of both permeable and impermeable seeds. The permeable proportion of seeds present in a lot collected from Suzhou, China, was separated using an imbibition test. The permeable proportion had an average moisture content of 15.6 %, compared with 8.5 % for impermeable seeds. Drying permeable seeds above silica gel to 10 % and 8 % f. wb., resulted in 77 and 100 % impermeable seeds, respectively, compared with no impermeable seeds at 15 % moisture content. Dried to 10 % moisture content, and incubated above water in an airtight container, 46 % of the seeds reverse impermeability. Permeable seeds with 15 % moisture content maintained above LiCl2 (RH=70 %) did not develop impermeability after three months of storage. The seeds dried to 6 % moisture content and stored above water in an airtight container showed no increase in moisture. Based on these results, we conclude that there is a strong relationship between moisture content and the onset of impermeability in this species. <![CDATA[Paleodistribution of Neotropical species of <em>Erythroxylum</em> (Erythroxylaceae) in humid and dry environments]]> ABSTRACT Variation in environmental conditions during the Quaternary period served as important filters for the maintenance of vegetation types and for determining the composition of the current biota. We analyzed oscillations in the distributions of different vegetation types in Brazil during the Quaternary period using species of the genus Erythroxylum (Erythroxylaceae) because of the vast heterogeneity of habitats in which they occur. We hypothesized that it would be possible to observe geographically distinct distribution patterns of species of Erythroxylum as a result of the climate changes that occurred during the last glacial maximum (LGM) and in the last interglacial period (LIG) of the Pleistocene. We used bioclimatic variables to elaborate distribution models of 11 species under three scenarios: the current climate, LGM, and LIG. We found four plant distribution patterns in humid and semiarid climates. During the LIG, humid patterns were restricted to northeastern and central-western Brazil, while semiarid conditions maintained plant distributions in the same regions of Brazil where they occur today, although with additionanl occurrences in the northern and central-western portions of that country. During the LGM, all distribution patterns exhibited extensions towards the coast due to the exposure of the continental shelf. <![CDATA[Role of glutathione in tolerance to arsenite in <em>Salvinia molesta</em>, an aquatic fern]]> ABSTRACT In many plant species, tolerance to toxic metals is highly dependent on glutathione, an essential metabolite for cellular detoxification. We evaluated the responses of glutathione metabolism to arsenite (AsIII) in Salvinia molesta, an aquatic fern that has unexplored phytoremediation potential. Plants were exposed to different AsIII concentrations in nutrient solution for 24 h. AsIII caused cell membrane damage to submerged leaves, indicating oxidative stress. There was an increase in the glutathione content and ϒ-glutamylcysteine synthetase enzyme activity in the submerged and floating leaves. The glutathione peroxidase and glutathione sulfotransferase enzymes also showed increased activity in both plant parts, whereas glutathione reductase only showed increased activity in the submerged leaves. These findings suggest an important role for glutathione in the protection of S. molesta against the toxic effects of AsIII, with more effective tolerance responses in the floating leaves. <![CDATA[Floral and reproductive biology of <em>Alcantarea nahoumii</em> (Bromeliaceae), a vulnerable endemic species of the Atlantic Forest]]> ABSTRACT Alcantarea nahoumii occurs exclusively in the state of Bahia, Brazil, and is classified as vulnerable due to deforestation and frequent fires in the region. Knowledge of floral and reproductive biology is fundamental to understanding ecological interactions, as well as the reproductive success of plant species. The objective of this study was to evaluate the floral and reproductive biology of A. nahoumii in an Atlantic Forest fragment with regard to phenology, pollen viability, stigma receptivity, pollination ecology and reproductive systems, all of which are important parameters for of the development of conservation strategies for the species. Anthesis is diurnal and heterogeneous, starting at 6:30 a.m. and lasting until 8:00 a.m. Highest germination percentages and greatest pollen tube lengths were obtained in BK culture medium. Histochemical tests revealed high pollen viability (89.71 %). Stigma receptivity occurred during anthesis and lasted for up to 24 hours after floral opening. Alcantarea nahoumii exhibited preferential allogamy and self-compatibility, and required a pollinator to production of viable seeds. Sixteen species of pollinators were observed visiting A. nahoumii, among which were five hummingbird species. Even though its reproductive system is efficient, this bromeliad remains threatened mainly due to habitat fragmentation caused by deforestation, burning and predatory extractivism. <![CDATA[Evidence of the effects of fire on branching and leaf development in cerrado trees]]> ABSTRACT We discuss evidence of effects of an accidental fire on shoot growth and leaf development in six cerrado tree species with distinct leaf phenologies. Buds of all six species were marked before shoot and leaf emergence in the dry season. After fire, leaf and shoot growth were monitored weekly and specific leaf area (SLA) was determined. Shoot order was determined in the growing season. Evergreens and semideciduous woody species had rapid leaf and shoot growth and decreased leaf life span (LLS) after fire compared with published data for evergreens in cerrado areas without fire. On the other hand, Kielmeyera variabilis, a deciduous species, showed intense branching and produced two orders of shoots in one growing season. Fires promote rapid leaf and shoot growth in evergreens owing to reserve accumulations that allow survivorship after disturbances. However, the leaves produced by evergreens after fire had high SLAs and were discarded before the next rainy season (short LLS). This leaf cohort was produced with less carbon per leaf, and the decreased LLS prevented herbivory and water loss during the dry season. Fire is an important factor of cerrado environments, influencing leaf production and shoot architecture in cerrado trees. <![CDATA[Composition, diversity and structure of vascular epiphytes in two contrasting Central Amazonian floodplain ecosystems]]> ABSTRACT Research focusing on assemblages of vascular epiphytes in the Amazon are scarce. This is especially true for Amazonian floodplain forests, for which only two previous studies have been published. We compared composition, richness and structure of epiphyte assemblages in white-water and black-water floodplains (várzea and igapó) in Central Amazonia in order to close knowledge gaps concerning the distribution and richness of epiphytes. We established sixteen 25x25 m plots in each forest type, and counted and identified all species of vascular epiphytes occurring on trees with a diameter at breast height (DBH) ≥10 cm. We observed a clear distinction in epiphytic species composition (r2=0.83, p=0.001) and diversity (t=3.24, P=0.003) between the two environments, with 61.5 % of species being restricted to várzea, 22.9 % restricted to igapó and only 15.6 % common to both ecosystems. The floodplains were also structurally different for the most abundant species and those with the highest Epiphytic Importance Value (IVe). The diversity of trees did not influence the epiphyte diversity in either ecosystem. The forests were found to differ in the composition, diversity and structure of their epiphytic assemblages, which must be taken into account when designing conservation action plans for these ecosystems and for their vascular epiphytes. <![CDATA[Asteraceae in the northern Espinhaço Range, Brazil: richness, endemism and conservation]]> ABSTRACT Floristic inventories focussing on the Espinhaço Range have revealed an extensive diversity for Asteraceae and emphasize the high degree of endemism of its species. This study aims to explore the species-rich Asteraceae through a floristic survey, and by identifying endemic records for the municipality of Morro do Chapéu, Bahia. Samples were collected during six field trips in different phytophysiognomies and approximately 1,400 exsiccatae from the main herbaria collections were examined. Asteraceae in Morro do Chapéu is represented by 18 tribes, 72 genera and 119 species. Eupatorieae and Vernonieae are the most species rich tribes and currently comprise 30 and 28 species, respectively, representing 50 % of the local Asteraceae flora. Baccharis represents the richest genus with seven species, followed by Lepidaploa and Mikania with six species each. Species belonging to Eupatorieae, namely Acritopappus santosii, Acritopappus sp. nov., Lapidia apicifolia, Stylotrichium edmundoi, Scherya bahiensis, Trichogonia tombadorensis and, additionally, a new species of Vernonieae, Stilpnopappus sp. nov., are endemic to the municipality. We provide a checklist and identification key for the species, and report the occurrence of endemism and their importance for the biological conservation. <![CDATA[Miocene fern spores and pollen grains from the Solimões Basin, Amazon Region, Brazil]]> ABSTRACT This work documents fern spores and pollen grains (miospores) recovered from rocks of the Solimões Formation (Solimões Basin), their botanical affinities, ecology and distribution in the Miocene of the Amazon Region. The assemblage of miospores is well preserved and diverse. They are identified, illustrated and assigned to the ten families of ferns and 22 families of spermatophytes. All miospores were identified to the taxonomic level of species except for two taxa (Perinomonoletes and Podocarpidites). The families Pteridaceae and Arecaceae were most representative of ferns and spermatophytes, respectively. This work contributes to the knowledge of the paleoflora and will aid in paleoenvironmental, paleoecological and biostratigraphic interpretations of the Miocene of the Amazon Region. <![CDATA[Intraspecific variation in seed size and light intensity affect seed germination and initial seedling growth of a tropical shrub]]> ABSTRACT Seed germination and seedling performance are affected by environmental factors and seed traits. In this study we investigated the effects of seed size and light intensity on germinability and seedling development of Copaifera oblongifolia. A total of 225 seeds were individually weighed and sown in three germination trays composed of 75 cells each. Each tray was placed in a different germination chamber with controlled photoperiod, temperature and light intensity. Seed size showed a positive relationship with time required for seed germination, and seeds exposed to high light intensity required more time to germinate. Seed size did not affect germination percentage, but seeds sown under high light intensity had a lower germination percentage than seeds sown under low light intensity and darkness. Seedling shoot mass showed a positive relationship with seeds mass, and seedlings grown in high light intensity had greater shoot mass than seedling growth in low light intensity and darkness. Thus, seed germinability of C. oblongifolia was higher in darkness while seedlings exhibited greater development under light. Looking to explain the ability of C. oblongifolia to colonize open/disturbed sites, it seems possible that plowing soil can bury seeds, thereby stimulating the germination of seeds present in the seed bank.