ResumoAnalisamos a variação funcional entre espécies decíduas (ED) e sempre verdes (ESV) para compreender as divergências nas estratégias de tolerância e evitação à seca. O estudo foi realizado em um fragmento de floresta tropical sazonalmente seca, localizada no munícipio de Pentecoste (3°47'S, 39°16'W), Ceará, Brasil. Mensuramos 17 traços funcionais foliares em 17 ED e cinco ESV, sendo 12 morfofuncionais, um fenológico e quatro fisiológicos. Verificamos que as ED exibiram maior taxa de fotossíntese por massa (A massa ), menor longevidade foliar (LF) e massa foliar específica (MFE) quando comparadas às sempre verdes. Esses traços foram considerados traços-chaves preditores das estratégias de evitação e tolerância à seca. As ED e ESV apresentaram uma demanda conflitante entre tolerância à seca e taxa fotossintética, pois a LF foi negativamente correlacionada com à A massa . Embora tenham demonstrado diferenças claras na MFE e LF não observamos diferenças significativas na A área e g s , consequentemente, ED e ESV não diferiram na eficiência no uso da água durante o período chuvoso. Apesar da variabilidade substancial dentro do grupo, todas as ED exibem estratégia de evitação à seca enquanto que ESV exibem um conjunto de traços funcionais foliares relacionados a estratégia de tolerância à seca. Palavras-chave: Grupos fenológicos, tolerância à seca, evitação à seca. AbstractWe analyzed the functional variation between deciduous and evergreen species to understand the differences across the strategies of avoidance and tolerance to drought. Our study was carried in a fragment of seasonally dry tropical forest located in the city of Pentecoste (3°47'S, 39°16'W), Ceará, Brazil. We measured 17 functional leaf traits in 17 deciduous and five evergreen species, being 12 morphofunctional, one phenological and four physiological. We found that deciduous species exhibited greater A mass , lower leaf lifespan (LL) and leaf mass per area (LMA) than evergreen species. These traits were considered key predictor traits of avoidance and drought tolerance strategies. Deciduous and evergreen species showed a trade-off between drought tolerance and photosynthetic rate, LL was negatively correlated with A mass . Although we have shown clear differences in LMA and LL not observed significant differences in A area and g s , consequently, deciduous species and evergreen species did not find significant differences in WUE i and WUE. Despite substantial variability within the group, all deciduous species fall predominantly in the drought avoidance strategy, while evergreen species display a suite of traits related to drought tolerance.

Deciduous and evergreen trees are usually considered the main coexisting functional groups in seasonally dry tropical forests (SDTF). We compared leaf and stem traits of 22 woody species in the Brazilian Caatinga to investigate whether deciduous (DC) and evergreen (EV) species have divergent water-use strategies. Our hypothesis was that DC trees compensate for their short leaf longevity by being less conservative in water use and showing higher variation in the seasonal water potential after leaf shedding. Evergreen species should exhibit a highly conservative water use strategy, which reduces variations in seasonal water potential and the negative effects of desiccation. Our leaf dynamics results indicate that the crown area of DC trees is more sensitive to air and soil drought, whereas EV trees are only sensitive to soil drought. Deciduous species exhibit differences in a set of leaf traits confirming their acquisitive strategy, which contrasts with evergreen species. However, when stomatal traits are considered, we found that DC and EV have similar stomatal regulation strategies (partially isohydric). We also found divergent physiological strategies within DC. For high wood density DC, the xylem water potential (Ψ xylem ) continued to drop during the dry season. We also found a negative linear relationship between leaf life span (LL) and the transpiration rate per unit of hydraulic conductivity (Λ), indicating that species with high LL are less vulnerable to hydraulic conductivity loss than early-deciduous species. Collectively, our results indicate divergence in the physiology of deciduous species, which suggests that categorizing species based solely on their leaf phenology may be an oversimplification.

Foliar uptake of dew is likely an important mechanism of water acquisition for plants from tropical dry environments. However, there is still limited experimental evidence describing the anatomical pathways involved in this process and the effects of this water subsidy on the maintenance of gas exchange and leaf lifespan of species from seasonally dry tropical vegetation such as the Brazilian caatinga.• We performed scanning electron, bright-field and confocal microscopic analyses and used apoplastic tracers to examine the foliar water uptake (FWU) routes in four woody species with different foliar phenology and widely distributed in the caatinga. Leaves of plants subjected to water stress were exposed to dew simulation to evaluate the effects of the FWU on leaf water potentials, gas exchange and leaf lifespan.• All species absorbed water through their leaf cuticles and/or peltate trichomes but FWU capacity differed among species. Leaf wetting by dew increased leaf lifespan duration up to 36 days compared to plants in the drought treatment. A positive effect on leaf gas exchange and new leaf production was only observed in the anisohydric and evergreen species.• We showed that leaf wetting by dew is relevant for the physiology and leaf lifespan of plants from seasonally dry tropical vegetation, especially for evergreen species.

Although the conservation of tropical biodiversity depends on protected areas, there is still a very large 'gap' of knowledge on the flora of Brazilian reserves, especially in the Northeast region of Brazil. Field and herbarium surveys of the phanerogamic flora of the Ubajara National Park, located on the Brazilian Northeast, were made and analyses on phenology and dispersal syndromes were performed. 418 taxa (213 trees and shrubs, 100 terrestrial herbs, 68 climbing plants, 33 sub-shrubs, two epiphytes, one hemiparasite and one aquatic herb) were recorded. The most representative families were: Fabaceae, Malvaceae, Asteraceae, Rubiaceae and Euphorbiaceae. The annual flowering / fruiting peak hypothesis was not fully confirmed, therefore, the forest may be an important food resource for the fauna all year long (especially in the moister region). Zoochory was the predominant dispersal syndrome in the moister area, whereas, autochory and anemochory together, predominated in the drier area.

The relative importance of different community assembly mechanisms varies depending on the environment. According to the stress-dominance hypothesis (SDH), assembly mechanisms range from strong abiotic filtering to competition as the environment becomes more favourable. Most evidence for the SDH comes from studies in gradients of conditions (i.e. abiotic environmental factors that influence the functioning of organisms but are not consumed by them). However, we hypothesized that in resource gradients, competition increases as abiotic filtering becomes stronger. To test our hypothesis, we set up eight plots at different sites along an abiotic severity gradient in the Brazilian semi-arid region (BSAR). In each plot, we identified and measured each woody plant species found, and we recorded 11 functional traits of the main species, dividing the traits into alpha (competition effects) and beta (abiotic filtering effects). We investigated the presence of phylogenetic signal in the traits, the community phylogenetic and phenotypic patterns, and associated the variation in these patterns with the availability of water and soil nutrients. We found phylogenetic signal for most (91%) of the traits analysed. The phylogenetic patterns varied from clustered in stressful sites to random or overdispersed in favourable sites, and we concluded that these phylogenetic patterns were the result of historical processes influencing community assembly in different environments in the BSAR. In general, the phenotypic patterns varied from clustered at the most stressful end to random at less stressful sites. Our results show that in resource gradients, any restriction of the resource (hydric or edaphic) intensifies abiotic filtering and, at the same time, increases the competitive hierarchy among species. On the other hand, stochastic processes seem to have a stronger influence under more favourable abiotic conditions, where abiotic filtering and competition are weaker. Thus, we conclude that the SDH is not supported in resource gradients.

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Resumo Afloramentos rochosos são relevos residuais montanhosos que ocorrem em regiões tropicais, subtropicais e temperadas de todo o mundo. Nesse trabalho, nossos objetivos foram entender os padrões de riqueza e similaridade florística de plantas trepadeiras em afloramentos rochosos no nordeste do Brasil, bem como, compreender aspectos morfológicos e formas de dispersão dessas espécies. As análises foram realizadas utilizando uma lista florística de plantas trepadeiras registradas em inventários de afloramentos rochosos, nos estados da Paraíba e Pernambuco. Foram identificadas 143 espécies, 66 gêneros e 25 famílias. Quanto ao aspecto morfológico, 72% das espécies são trepadeiras herbáceas e 28% são lenhosas (lianas). O mecanismo de ascensão mais frequente foi o volúvel (66%) e a síndrome de dispersão mais representativa foi autocoria (44%). A riqueza de trepadeiras herbáceas e lenhosas foi positivamente correlacionada com a altitude e negativamente correlacionada com a distância do litoral e a temperatura; correlação negativa também foi observada entre a riqueza de trepadeiras herbáceas e a precipitação, enquanto para as lenhosas a riqueza se manteve constante nessa variável. A análise de similaridade florística resultou na formação de três grupos, sugerindo uma composição florística característica da matriz circundante, influenciada por fatores abióticos e tipos vegetacionais onde os afloramentos rochosos estão inseridos.

Background: Factors determining coexistence of the species have been recognized out since Darwin, but empirical studies have brought the relationship between niche similarity and competition into question. Knowing the mechanisms of coexistence makes it possible to predict biological invasions and determine better species combinations for the restoration and recovery of degraded areas. This study aimed to test the competition-relatedness hypothesis for semiarid tree species. Thus, an experiment was carried out with a phylogenetic gradient of tree species, planted in pairs. The phylogenetically closest pair consisted of congeneric species of the same clade, the intermediate pair comprised congeneric species of distinct clades, and the more distant pair were species of the same family. Results:Our results show that the phylogenetically closest and the more distant pairs corroborated the competition-relatedness hypothesis, but the presence of one species with high competitive ability in the intermediate pair caused an unexpected pattern. Conclusion:Niche differences are important for coexistence, but it is necessary to know the competitive ability of each species and the specific associations that are more productive to improve the efficiency of restoration programs and to reveal the degree of aggressiveness in the case of invasive species.