Acta Botanica Brasilica, Volume: 33, Issue: 3, Published: 2019
  • Spores of Plagiochila (Dumort.) Dumort.: the taxonomic relevance of morphology and ultrastructure Articles

    Silva-e-Costa, Juliana da Costa; Luizi-Ponzo, Andrea Pereira

    Abstract in English:

    ABSTRACT Plagiochilaceae is a family of leafy liverworts that are distributed worldwide. It is of great importance due to its taxonomic and ecological implications among bryophytes. Most species of the family belong to the genus Plagiochila, but there is no consensus regarding its infrageneric circumscription. There have been few palynological studies involving Plagiochilaceae and Plagiochila. Here, we describe the spore morphology of seventeen species of Plagiochila and discuss the taxonomic value of palynological characters for these taxa. The spores were processed by standard palynological techniques and analyzed using light and electron microscopy. The spores were found to be apolar, spheroidal, released monads that vary in size from 13µm to 58µm (small to large size). The sporoderm comprises an intine (stratified), a nexine, and a sexine. The spore surface is ornamented with granules that vary in shape and morphology, thus allowing the studied species to be grouped into four spore types: regular and delicate granulate, irregular and coarse granulate, long granules with flattened apices, and long and straight granules. Hierarchical cluster analysis revealed five different groups of species, evidencing the importance of spore information for taxonomic and phylogenetic studies.
  • Restoration of abandoned subtropical highland grasslands in Brazil: mowing produces fast effects, but hay transfer does not Articles

    Thomas, Pedro Augusto; Overbeck, Gerhard Ernst; Müller, Sandra Cristina

    Abstract in English:

    ABSTRACT Subtropical Campos Sulinos grasslands, in South Brazil, are among the most biodiverse grasslands of the world. As climatic conditions lead to high productivity, disturbance are critical to maintain their diversity. Long-term exclusion, on the other hand, leads to plant species losses and changes in composition. No studies on the restoration of these grasslands after abandonment exist to date. We tested combinations of restoration techniques with the aim of increasing plant diversity in an abandoned and species-poor grassland in the South Brazilian highland region. In a bi-factorial experiment, we tested the effects of two different frequencies of mowing and of hay transfer. Mowing reduced plant cover, vegetation height, and abundance of erect grasses and shrubs, and increased species richness, diversity (Shannon diversity index) and prostrate forb and grass cover. No differences were found between mowing frequencies. Hay transfer was not effective at reintroducing species. The results of the present study provide further evidence that the reintroduction of plants is a major challenge in the restoration of subtropical and tropical grasslands. The study shows that mowing is a fast way to increase plant diversity in Campos Sulinos after long periods of abandonment.
  • Spore diversity among species of Blechnaceae in the Atlantic Forest Articles

    Silva, Dilma Melo da; Sylvestre, Lana da Silva; Mendonça, Cláudia Barbieri Ferreira; Gonçalves-Esteves, Vania

    Abstract in English:

    ABSTRACT The palynological diversity of Blechnaceae in the Atlantic Forest was investigated. While the monophyletic family belongs to the group of leptosporangiate ferns, a new classification proposed by recent phylogenetic study reorganizes the family and adds new genera. To expand palynological knowledge of the group, the spore morphology of 23 species and a hybrid, distributed among 10 genera, was described. Material from herbarium collections were submitted to acetolysis and mounted on slides, with subsequent statistical analysis of spore measurements. Photomicrographs of the material were taken under both light and scanning electron microscopy. Perine ornamentation varied among psilate, rugulate and scabrate; granules and gemmae were present along with thin, smooth cristae. Species of Blechnum and Austroblechnum exhibited the greatest diversity. The attributes of the spores obtained here were able to differentiate the analyzed species, although the spore morphology of some taxa was found to be very similar. Multivariate analysis assessed the relevance of quantitative data for differentiating the taxa.
  • Elevated atmospheric CO2 concentration improves water use efficiency and growth of a widespread Cerrado tree species even under soil water deficit Articles

    Souza, João Paulo; Melo, Nayara Magry Jesus; Halfeld, Alessandro Dias; Vieira, Kamilla I. C.; Rosa, Bruno Luan

    Abstract in English:

    ABSTRACT Changes in atmospheric CO2 levels are accompanied by ecological interactions involving other environmental factors, such as drought, which can severely alter the water balance of plants, thereby influencing sap flow, gas exchange, and plant growth. The objective of this study was to evaluate the water use economy, leaf gas exchange, and growth of young plants of the species Lafoensia pacari subjected to high concentrations of atmospheric CO2 ([CO2]) and soil water deficit. Increased vapor pressure deficit was observed from 1200 to 1800 hours. Plants under elevated [CO2] exhibited increased leaf photosynthesis, resulting in improved growth. Specific leaf area was lower in plants under high [CO2], mainly after soil water deficit treatment. Daily irrigated plants growing under ambient [CO2] had higher stem sap flow velocity (cm h-1) and hourly sap flow (kg h-1), mainly during the hottest hours of the day, than plants under high [CO2]. Improved water use by plants growing under high [CO2] may result in increased availability of water in the soil, partially offsetting future drought events and extending the growth period.
  • Genetic evidence of multiple reproductive strategies in a microendemic and threatened cactus (Cactaceae: Discocactus Pfeiff) in Bahia, Brazil Articles

    Jesus, Izabela Santos Dias de; Conceição, Leila Patricio; Schnadelbach, Alessandra Selbach; Assis, José Geraldo de Aquino; Carvalho, Maria Luiza Silveira de

    Abstract in English:

    ABSTRACT Discocactus zehntneri subsp. petr-halfari, an endangered taxon, is represented by a single population in an anthropized area of Bahia, Brazil, where it is suffering due to extreme extractivism. Thus, information about this cactus, such as its reproductive patterns, is urgently needed to support conservation strategies. A population genetics approach was used to determine if this subspecies has a preferential pattern of reproduction. We sampled 18 individuals, both with and without connection to parental plants, from five clumps and assessed their diversity and genetic structure using five ISSR markers. The results revealed two clumps that are genetically supported by the presence of genetically equal individuals. The other three groups presented individuals that are genetically different and similar to individuals in other clumps. These findings suggest that this subspecies has sexual and clonal reproduction and that its environmental distribution might be shaped by events of dispersion. In addition, a possible hybrid origin may explain its rates of genetic diversity. Despite all these factors, this taxon is in danger and so the development of conservation strategies to preserve its population are urgently needed, including in situ and ex situ actions such as the micropropagation in vitro, living collections and cryopreservation.
  • Global warming decreases the morphological traits of germination and environmental suitability of Dipteryx alata (Fabaceae) in Brazilian Cerrado Articles

    Ribeiro, Raquel Menestrino; Tessarolo, Geizianne; Soares, Thannya Nascimento; Teixeira, Itamar Rosa; Nabout, João Carlos

    Abstract in English:

    ABSTRACT We experimentally evaluated how different temperatures affect germination of individual seedlings of Dipteryx alata, and estimated the impact of climate change on the species using ecological niche modeling. A total of 240 seeds were randomly distributed among three different temperature treatments (32 ºC, 36 ºC, and 40 ºC), and monitored for 35 days. We measured seven seed traits and estimated the ecological niche of D. alata using a consensus of four methods. The treatment with the highest temperature produced smaller and lighter seedlings. The consensus of ecological niche modeling indicated that are expected to reduce the areas with climates favorable for D. alata in future scenarios. Thus, our two results (experiment and ecological niche modeling) are concordant, and both indicate the impact of global warming on germination (initial stage of the plant) and potential geographic distribution. Moreover, in geographic context, our experiment and ecological niche modeling indicated that north, northwest and central regions of the “Cerrado” are predicted to have lower morphological traits of germination and loss climate favorable area, since these regions are predicted to have higher temperatures (nearly 40 ºC) in future climatic scenarios.
  • Assessment of the dendrochronological potential of Licaria bahiana Kurz, an endemic laurel of lowland Atlantic forests in Brazil Articles

    Fontana, Cláudia; Santini-Junior, Luiz; Olmedo, Gabriela Morais; Botosso, Paulo César; Tomazello-Filho, Mario; Oliveira, Juliano Morales

    Abstract in English:

    ABSTRACT The Atlantic Forest of southeastern Brazil has been considered to have the highest number of tree species per hectare in the world. Assessing the influence of climate on tropical tree species is a priority in the face of ongoing climate change, and for which dendrochronological studies have been important. We address the dendrochronological potential of Licaria bahiana Kurz (Lauraceae), an endemic species of the Atlantic forests. We studied growth ring anatomy of L. bahiana and applied dendrochronological methods to investigate how short-term variation in climate affect its radial growth. Distinct growth rings were observed in all individuals and demarcated by darker tangential fiber zones in latewood. Trees showed high climatic sensitivity (0.48) and growth synchrony (intercorrelation r = 0.69; rbar = 0.38). Radial growth was negatively influenced by high temperatures at the beginning of the current growing season (r = -0.46) and by excessive rainfall at the end of the current growing season (r = -0.29), which are periods that correspond to the phenological reproductive phases of the species. Climate anomalies during this period may alter the tradeoff between growth and reproduction, in favor of the latter.
  • Factors driving seed dispersal in a Neotropical river-floodplain system Articles

    Fernández, Florencia Facelli; Schneider, Berenice; Zilli, Florencia

    Abstract in English:

    ABSTRACT Dispersal is a key process affecting the diversity of natural communities. We addressed hydrochory of wetland plant seeds in the Middle Paraná River floodplain. We first studied seed dispersal by drifting macrophytes in the Paraná River main channel (MC), in a high discharge secondary channel (HD) and in two low discharge channels (LD) during an extraordinary flood. We then experimentally analyzed the effect of standing (SW) and moving water (MW) on seed buoyancy of different plant communities. We recorded seeds of 27 taxa distributed in 12 families. Taxa richness ranged from 17 in LD to 25 in MC, and included seeds of terrestrial, palustrine and aquatic plants. River discharge did not affect seed richness and density, which was probably associated with a homogenization process caused by the flood. Seed buoyancy significantly differed between water movement treatments independently of the source community, lasting longer in SW than in MW. Our results suggest that drifting macrophytes contribute to seed dispersal of several communities in the Middle Paraná River, and probably over long distances. Furthermore, seed buoyancy might be more important for surficial dispersal in low-energy systems, where subaqueous dispersal may be difficult due to the lack of current.
  • Pollen morphology of the Brazilian species of Bernardia Houst. ex Mill. and Tragia L. (Euphorbiaceae, Acalyphoideae) Articles

    Santos, Mirane de Oliveira; Lima, Luciene Cristina Lima e; Sales, Margareth Ferreira de; Silva, Juliana Santos

    Abstract in English:

    ABSTRACT Bernardia and Tragia are the largest genera of the tribes Bernardieae and Plukenetieae (Euphorbiaceae,), with 68 and 125 species, respectively. Very few palynological studies have focused specifically on these genera in spite of the great pollen diversity observed in the family. The present study analyzed the pollen morphology of the Brazilian species of Bernardia and Tragia to identify diagnostic characteristics that could aid in their taxonomic circumscription. The pollen grains of 11 species of Bernardia and five of Tragia were obtained from specimens deposited in the HRB, HUEFS, PEUFR, RB and UFP herbaria, and were analyzed using light and scanning electron microscopy. The analyzed species had small- to medium-sized pollen grains in monads, with shapes from prolate to subprolate. The most significant differences were observed in aperture type and exine ornamentation. The pollen grains of Bernardia are tricolporate, with aperture margins varying from narrow to wide or with just slightly evident margins, and the exine varying between microreticulate and microreticulate-perforate. The pollens of Tragia are tricolpate with the exine varying between intectate pilate and verrucate. Some species of both genera could be diagnosed based on unique pollen characters, and four distinct morphological groups of Bernardia and two of Tragia were observed.
  • Increased atmospheric CO2 changes the photosynthetic responses of Acrocomia aculeata (Arecaceae) to drought Articles

    Rosa, Bruno Luan; Souza, João Paulo; Pereira, Eduardo Gusmão

    Abstract in English:

    ABSTRACT Water availability is the main factor that explains current patterns of palm abundance. However, the interaction between water stress and increasing atmospheric CO2 concentrations caused by climatic change and its effects on palm physiology remain poorly known. Macauba palm is a widespread Neotropical species commonly found in ecosystems subjected to seasonal drought and has potential use in oil production. The present work investigated the influence of increased CO2 concentrations on photosynthetic responses to drought in macauba palm plants. Exposure to increased CO2 concentrations led to up-regulation of photosynthesis through higher stomatal conductance and improved light and water use efficiency. Macauba palm plants under water stress, irrespective of CO2 concentration, were able to maintain constant levels of proline and chlorophyll, while preventing oxidative damage. Plants grown at higher CO2 concentrations were more capable of recovering from drought due to higher Rubisco carboxylation rate (Vc max) and electron transport rate (J max), which prevented a reduction in total dry mass at the end of the stress period. Stomatal control of photosynthesis, coupled with the prevention of severe damage under stress, would allow efficient biomass production by the macauba palm under future scenarios of climate change.
  • Vascular flora of Lençóis Maranhenses National Park, Maranhão State, Brazil: checklist, floristic affinities and phytophysiognomies of restingas in the municipality of Barreirinhas Articles

    Rodrigues, Misael Lira; Mota, Nara Furtado de Oliveira; Viana, Pedro Lage; Koch, Ana Kelly; Secco, Ricardo de S.

    Abstract in English:

    ABSTRACT This study presents a floristic survey of the vascular plants of restingas of Lençóis Maranheses National Park, in the municipality of Barreirinhas, Maranhão, Brazil, including descriptions of the principal phytophysiognomies and similarity analyses including other restinga areas in North and Northeastern Brazil. Samples from the study area deposited in the herbaria MG, IAN and MAR were inventoried and fieldwork for the collection of additional botanical samples was undertaken between September 2015 and August 2017. Unweighted pair group method with arithmetic mean (UPGMA) using Jaccard index was used to calculate the similarity among floras of the restingas of the states of Pará, Piauí, Ceará and Maranhão. A total of 289 species in 189 genera and 73 families was recorded, including 56 new occurence records for the state of Maranhão. The richest families were Poaceae, Cyperaceae, Fabaceae, Rubiaceae, Eriocaulaceae and Myrtaceae. Similarity indexes revealed low similarity among the selected areas, suggesting high floristic identity for each area, as well as possible collection bias among the areas.
  • Soft-bodied benthic algae in pristine Brazilian streams: from acid to karst Articles

    Fonseca, Bárbara Medeiros; Feijó, Lidia Mendes; Mendonça-Galvão, Luciana de

    Abstract in English:

    ABSTRACT This study evaluated soft-bodied benthic algae from seven streams located in protected areas of central Brazil (Parque Nacional de Brasília, Parque Nacional da Chapada dos Veadeiros and Parque Estadual de Terra Ronca), and related them to abiotic factors. We addressed the following questions: A) how algal community structure in Cerrado streams is influenced by the marked seasonality typical of the region; and B) how karst geology influences algal communities in Parque Estadual de Terra Ronca, as compared to streams in other Cerrado areas. Samples were collected between 2012 and 2013 from a single site in each stream, and upstream and downstream of caves present in Parque Estadual de Terra Ronca. Altogether, 159 taxa were recorded. Algal community structure varied significantly among sites, but not between seasons, despite relatively lower abundances during the rainy season, likely due to a negative influence of the faster currents in streams during this period. Some alkaliphilic species were observed only at sites near caves (e.g. the cyanobacterium Tolypothrix distorta), while acidophilic taxa were more frequent in the other streams (e.g. desmids and Cyanobacteria such as Scytonema caldarium, Hapalosiphon stuhlmannii and Stigonema ocellatum). We observed a rare green alga, Microthamnion kuetzingianum, and reported the cyanobacterium Rivularia aquatica for the first time in Brazil.
  • Post pollination events in a self-sterile hexaploid monoembryonic lineage of Handroanthus serratifolius (Vahl) S. Grose (Bignoniaceae) Articles

    Alves, Mariana Ferreira; Bittencourt, Nelson Sabino; Oliveira, Paulo Eugênio; Sampaio, Diana Salles

    Abstract in English:

    ABSTRACT In diploid late-acting self-incompatible (LSI) species of Bignoniaceae, self-pollinated pistils show a marked delay in ovule penetration by pollen tubes, followed by delayed, but otherwise normal, initial stages of endosperm development and subsequent pistil abscission. Most polyploid species of Bignoniaceae are apomictic and set selfed fruits with viable polyembryonic seeds carrying adventitious embryos. Handroanthus serratifolius is a polyploid species with sporophytic apomictic individuals that produce polyembryonic seeds after either self- or cross-pollination, and other LSI individuals that produce exclusively monoembryionic seeds. Our aim was to determine whether self-sterility events in the latter are similar to those observed in other diploid LSI species of Bignoniaceae. No conspicuous differences in the progress of ovule penetration, fertilization and early stages of endosperm development were observed between selfed and crossed pistils, which contrasts with the marked delay observed in these events after self-pollination in diploid LSI species of the family. Adventitious embryo precursor cells (AEPs) were observed in some ovules, but they apparently do not develop into embryos. We believe that the AEPs in these plants represent a ‘potential’ for sporophytic apomixis, which would explain the similar behaviour of post-pollination events in selfed vs. crossed pistils despite their inability to set fruits after selfing.
  • Reconstruction of the Late Pleistocene to Late Holocene vegetation transition using packrat midden and pollen evidence from the Central Mojave Desert Articles

    Balmaki, Behnaz; Wigand, Peter E.

    Abstract in English:

    ABSTRACT The Mojave Desert of the American West is characterized by plant species that reflect a unique mixture of winter precipitation and summer monsoon climate. Currently, the Mojave Desert experiences a strong summer monsoonal pattern with weak winter precipitation. Data from pollen and packrat midden analyses have revealed a history of Mojave Desert vegetation during the transition from the late Pleistocene to late Holocene (~17500 Cal. years B.P. to ~ 1200 Cal. years B.P.) that highlight a summer dominated monsoonal pattern, similar to those in the greater American Southwest. We compare pollen data from a lava tube in the Cima volcanic field, located in south-central region of the Mojave Desert, with plant macrofossil data from several woodrat midden localities in the region. The record for the Cima volcanic field reveals a vegetation history spanning the last ~ 8300 Cal. years B.P., with data from ancient woodrat middens detailing the record from ~17500 Cal. years B.P. to 7,800 Cal. years B.P. A Bryson macro-physical climate model for the transition from the late Pleistocene to the Late Holocene was created and compared to our findings to assess possible relationships between climatic variations and the arrival of diagnostic plant species within the Mojave Desert.
  • Risk of genetic vulnerability and aspects of the reproductive biology of Psychotria ipecacuanha (Rubiaceae), a threatened medicinal plant species of Brazilian forests Articles

    Silva, Patrícia Campos da; Nascimento, Talita Oliveira; Krause, Willian; Chaves, Douglas Siqueira de Almeida; Silva, Celice Alexandre

    Abstract in English:

    ABSTRACT Psychotria ipecacuanha, commonly known as Ipeca, is a medicinal plant of pharmacological and economic value. The species is distylous; it has populations with two floral morphs, one with long and one with short styles. Apart from the presence of two floral morphs in a balanced ratio (1:1), reciprocal herkogamy of the reproductive organs between alternative morphs is desirable to maintain cross-pollination. The risk factors for genetic erosion and conditions for sexual reproduction in natural populations of P. ipecacuanha were investigated. The main risks for genetic erosion in four populations studied were: habitat change in the forest fragment where they occurred and in the surrounding area over the last 20 years; proximity to agricultural areas; frequency of drought affecting the forest fragment; and the area occupied by the species within the forest fragment. All evaluated populations were isoplethic with the reciprocity of reproductive organs varying across populations. Anthropogenic factors, associated with morphological and reproductive characteristics (e.g., low reciprocity between anther and stigma and low pollen production), indicate risks for the maintenance and reproduction of Ipeca in the population of the municipality of Denise. Habitat loss, small clusters, and the low number of reproductive plants jeopardize the survival of the studied populations.
  • Improvement in light utilization and shoot growth in Hymenaea stigonocarpa under high CO 2 concentration attenuates simulated leaf herbivory effects Articles

    Maia, Renata A.; Fernandes, Geraldo W.; Silva, Advanio I. S.; Souza, João Paulo

    Abstract in English:

    ABSTRACT This study evaluated the photochemical responses of photosystem II and growth of Hymenaea stigonocarpa under CO2-enriched conditions with exposure to simulated herbivory events. After herbivory simulation in two distinct parts of the stem of plants (apex and base), chlorophyll a fluorescence, chlorophyll index, growth, extrafloral nectary density, leaf mineral nutrition, and biomass production were evaluated. Plants of H. stigonocarpa grown under high [CO2] after simulated herbivory in the apical part of the stem had higher electron transport rate, effective quantum yield of photosystem II, and chlorophyll contents. However, simulated herbivory in the basal portion of plants grown under high [CO2] increased plant height, branch and root length, leaf number, leaf area, node number, and leaf expansion rate. In conclusion simulated herbivory at the basal portion and high [CO2] induce positive responses in H. stigonocarpa, leading to the allocation of biomass to vegetative parts related to the capture of resources such as water and light. Apical leaves could compensate for the elimination of part of their leaf blades by increasing their photosynthetic yield. Thus, the increase of [CO2] attenuated the adverse effects of leaf removal on H. stigonocarpa plants by inducing photosynthetic improvement and growth after the loss of leaf tissue.
  • What is on the menu for frugivorous birds in the Cerrado? Fruiting phenology and nutritional traits highlight the importance of habitat complementarity Articles

    Maruyama, Pietro Kiyoshi; Melo, Celine; Pascoal, Camila; Vicente, Eduardo; Cardoso, João Custódio Fernandes; Brito, Vinícius Lourenço Garcia; Oliveira, Paulo Eugênio

    Abstract in English:

    ABSTRACT The relationship between plants and frugivorous animals is modulated by morphological and nutritional characteristics of fruits, as well as their seasonal availability across habitats. We evaluated fruiting phenology, fruit morphology and nutritional characteristics of 35 abundant plant species from 15 families associated with frugivorous birds from distinct habitats in the Cerrado (savanna, forest, and palm swamp). For a subset of 16 plant species, we also evaluated the overlap in interactions with frugivorous birds using data from the literature. Open-habitat plants had their fruiting peak during the rainy season, while fruiting of forest species was evenly distributed across the year. Plants of the same family exhibited similar fruit morphology and nutritional characteristics. Most plants had fruits with more sugars than lipids, while all species with higher lipid content were from savanna habitats and produced fruits during the rainy season, the peak reproductive season for birds. Assemblages of frugivorous birds exhibited considerable overlap, irrespective of habitat or fruiting season of plants. The complementarity found among habitats, considering seasonal availability and nutritional profile of fruits for frugivorous birds, is relevant for community maintenance and regeneration. Therefore, this landscape level complexity should always be considered in conservation and restoration policies for the Cerrado.
  • Pollen morphology and exine ultrastructure of Brasiliocroton P.E. Berry & Cordeiro (Euphorbiaceae) Articles

    Souza, Lidian Ribeiro de; Santos, Francisco de Assis Ribeiro dos; Carneiro-Torres, Daniela Santos

    Abstract in English:

    ABSTRACT The present study aimed to morphologically characterize the pollen grains of species of Brasiliocroton mamoninha and B. muricatus in order to expand palynological knowledge of the group and provide additional micromorphological information useful for studies of the relationships within Crotoneae. Polleniferous material was acetolysed and described using light, scanning electron and transmission microscopy. The pollen grains of the two species of Brasiliocroton were apolar, spherical, inaperaturate and medium-sized with a Croton ornamentation pattern. The Croton pattern of B. mamoninha is formed by subtriangular pila, >5-plicate with pointed apices, while for B. muricatus it is formed by subcircular to circular pila, <5-plicate with rounded apices. Ultrastructural analysis revealed a stratified sexine in both species, whereas variation in the pattern of deposition of the foot layer allowed the species to be palynologically distinguished from each other. The composition of the Croton pattern of ornamentation, the morphology of the ultrastructure of the wall and the range of variation in the diameter of the pollen grains differed between the studied species, and thus are diagnostic characters. Pollen morphology allowed the two species of Brasiliocroton to be palynologically separated, and provided data that will be useful for taxonomically circumscribing these taxa.
  • The genus Lepechinia Willd. (Lamiaceae - Salviinae) in Brazil Articles

    Antar, Guilherme Medeiros; Harley, Raymond Mervyn; Sano, Paulo Takeo; Drew, Bryan Thomas

    Abstract in English:

    ABSTRACT Lepechinia is a New World genus of Lamiaceae with ca. 45 species. There is ongoing controversy regarding the recognition and delimitation of Lepechinia that occur in Brazil. After fieldwork and herbaria consultation we recognize two species of Lepechinia in Brazil: Lepechinia speciosa, distributed within the Mantiqueira region, and Lepechinia annae, endemic to Serra do Caparaó. A taxonomic revision of the genus Lepechinia in Brazil is provided including descriptions, lectotypifications, a distribution map, a photographic plate, an identification key, a conservation assessment and comments on both the taxonomy and ecology of the two species.
  • The relationship between plant density and survival to water stress in seedlings of a legume tree Articles

    Honda, Eliane Akiko; Pilon, Natashi Aparecida Lima; Durigan, Giselda

    Abstract in English:

    ABSTRACT Competition for soil water is one of the major processes that drive the assembly of plant communities, particularly in regions subjected to long dry seasons. The relationship between plant density and soil water competition has strong, but poorly understood, practical implications for population dynamics, restoration and conservation. We planted seedlings of the pioneer legume tree Senegalia polyphylla in containers and assessed the effects of plant density on their resistance to water stress. We completely eliminated the above-ground parts (stem and shoots) of randomly selected plants at 60-days post-planting in order to create three different densities of seedlings. We saturated the soil of the remaining seedlings and then deprived them of additional water until all seedlings died. We assessed the time elapsed from water suppression to wilting and death of individual plants. We found a strong negative relationship between plant density and time to wilting or death. Seedlings survived water stress 80% longer when density was reduced by two-thirds. Planting in lower densities or reducing density by thinning should be considered as strategies to enhance resistance to water stress in drought-prone regions.
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