Eliane Regina da Silva

Diet-morphology relationship in the stream-dwelling characid Deuterodon stigmaturus (Gomes, 1947) (Characiformes: Characidae) is partially conditioned by ontogenetic development

Nos testamos se variacoes na composicao da dieta de uma populacao de Deuterodon stigmaturus podem ser explicadas por diferencas morfologicas entre individuos, e se as relacoes entre morfologia e dieta sao dependentes do desenvolvimento ontogenetico. A dieta de 75 individuos amostrados em um riacho costeiro do sul do Brasil foi analisada. Uma Analise de Coordenadas Principais (PCoA) foi utilizada para sumarizar variacoes individuais no conteudo estomacal. Os eixos retidos da PCoA foram testados como resposta ao comprimento padrao (CP) e ao comprimentos do intestino (CI) e da boca (CB), independentes do tamanho corporal, usando modelos lineares mistos (LMMs). Os itens macroscopicos mais consumidos por D. stigmaturus foram algas filamentosas (41%), plantas terrestres (20,3%), detritos (12%), e invertebrados terrestres (8,8%). Os LMMs mostraram que o CP foi positivamente relacionado ao consumo de plantas terrestres, enquanto que valores de CI independentes de CP foram negativamente relacionados ao consumo de invertebrados aquaticos e positivamente relacionados ao consumo de algas filamentosas. Quando o CP foi mantido constante, CB nao foi relacionado a composicao da dieta. As diferencas na dieta condicionadas ao tamanho corporal sugerem que os individuos mudam seu nicho trofico e funcao no ecossistema ao longo do desenvolvimento ontogenetico. As relacoes entre o tamanho do intestino e composicao da dieta sugerem diferencas individuais na habilidade de forragear e digerir itens alimentares distintos.

Phytotoxic effects of extract and essential oil of Eucalyptus saligna (Myrtaceae) leaf litter on grassland species

Under Eucalyptus plantations in the South Brazilian grassland region, few plants establish, and allelopathy may be involved in shaping this pattern. We aimed to assess the phytotoxicity of essential oil and aqueous extract of Eucalyptus saligna Sm. leaf litter on grassland species. We tested the effects of E. saligna pure oil and extract on germination, seedling growth, H2O2 levels and electrolyte leakage of seedling membranes of Paspalum notatum Flugge, Eragrostis plana Ness (Poaceae), Trifolium repens L. and Lotus corniculatus L. (Fabaceae). Essential oil and aqueous extract of E. saligna affected all recipient species, even at the lowest amounts/concentrations, inhibiting germination and initial growth, and also increasing H2O2 levels and electrolyte leakage of seedling membranes. Essential oil consisted mainly of monoterpenes and presented α-pinene and 1,8-cineole as the major compounds. The extract contained phenolics, and lower levels of these compounds in the extract were associated with decreased phytotoxicity. We conclude that E. saligna contains phytotoxic compounds in leaf litter that generate oxidative stress and lead to membrane damage, affecting seeds and seedling growth. In addition, we relate E. saligna phytotoxicity to monoterpenes that may be released from leaf litter by volatilisation, and phenolics that may be leached by rainfall. Our study indicates that E. saligna has allelopathic potential on the tested grassland species.

Does the phytotoxic shrub Heterothalamus psiadioides affect a plant community through allelopathy

Phytotoxicity has often been proposed as evidence of allelopathy. However, few studies have investigated allelopathy in natural field conditions. In South Brazilian grasslands, Heterothalamus psiadioides, a shrub establishing in dense stands, has shown strong phytotoxicity in laboratory assays. We conducted a field study to evaluate if this species also negatively affects a plant community through allelopathy. At a shrubland site, we established a phytotoxicity gradient, consisting of plots with H. psiadioides, plots with Baccharis patens—a shrub with minimal phytotoxicity—and plots without shrubs (no phytotoxicity). We assessed plant species cover, biomass, number of seedlings, diversity, richness, and plant community characteristics. Our study did not show evidences of plant inhibition near the phytotoxic species. We observed higher plant richness and diversity in plots with H. psiadioides than in plots with B. patens and without shrubs. The highest diversity near H. psiadioides was associated with greater forb cover, due to lower cover of dominant grasses. Differences in light incidence accounted for vegetation patterns more than allelopathic activity. Therefore, our study showed that the allelopathic potential of the evaluated species was overestimated based only on laboratory studies. We emphasize the relevance of conducting allelopathy studies in field and of having a similar species with low phytotoxicity in this kind of study. Results based only on laboratory assays and visual evidence of patterns in field may be misleading and may lead to an overestimation of the role of allelopathy in plant communities.

Comunidade de fungos Agaricomycetes em diferentes sistemas florestais no noroeste do Estado do Rio Grande do Sul, Brasil: Floresta Estacional Decídua e monocultura de eucalipto

Agaricomycetes fungi community at different forest systems in the northwest of Rio Grande do Sul State, Brazil: seasonal deciduous forest and eucalypt monoculture). Monocultures differ from native forests in relation to plant heterogeneity, variety of substrates, and soil humidity, possibly altering the diversity of organisms, such as the fungi. This study aimed to compare the richness, abundance, and composition of Agaricomycetes fungi in a native forest and in a eucalypt monoculture. The fungi were collected in a seasonal deciduous forest area and in a Eucalyptus grandis monoculture, in the northwest of Rio Grande do Sul State, Brazil. The abundance and richness of fungi were significantly lower in the eucalypt plantation than in the native forest and the species composition differed between the areas. Thus, it was concluded that the eucalypt monoculture negatively affects the Agaricomycetes fungi community.

Something old, something new in allelopathy review: what grassland ecosystems tell us

Allelopathy may be a relevant phenomenon in the dynamics of grasslands, a biome that presents high biodiversity and provides unique ecosystem services. Research on allelopathy in grasslands has been conducted worldwide and important suggestions to improve studies have been made in the recent past. However, few general patterns have been established so far. In this review, we report and discuss allelopathy research conducted in grassland ecosystems. We carried out a systematic search for allelopathy studies in grasslands and assessed descriptive, methodological and conceptual aspects of each article. We also evaluated if research quality has improved in recent years. We found that the studies investigated interactions mostly involving herbaceous species in many types of grasslands around the world. The studies have assessed the potential of allelopathy in structuring natural grasslands and artificial pastures and of applying allelopathy to bioherbicide development and to restoration of natural ecosystems. We observed inconsistency in terminology and discussed allelopathy definition. Moreover, we found that in recent years, allelopathy research has improved in some experimental design issues, but not in others. This shows that not all recommendations in literature have been taken into account. Otherwise, innovative methods and analytical tools have emerged. In spite of slow progress, allelopathy has shown potential relevance in dynamics and restoration of grasslands, as well as in weed management in cultivated systems. Thus, a better knowledge about allelopathy can lead to advances in science and in applied fields.

Phytotoxic effects of Heterothalamus psiadioides (Asteraceae) essential oil on adventitious rooting

Essential oils have many functions in plant development; among them, they take part in plant–plant interactions, such as allelopathy. The phytotoxicity of the essential oil of Heterothalamus psiadioides was evaluated on Arabidopsis thaliana adventitious rooting. This development process has demonstrated great sensitivity to phytotoxic essential oils and has been primarily studied by our research group. The essential oil of H. psiadioides showed highly negative effects on A. thaliana wild type (WT) adventitious rooting in very small amounts. As the hormone auxin has an important role on adventitious rooting, A. thaliana mutant superroot (sur1) that overproduces indole-3-acetic acid was tested to verify if it could better respond to the oil than WT. The mutant had a WT-like rooting response and the expression of its phenotype was not evident in treatments that had oil application. The essential oil also induced the generation of H2O2, a reactive oxygen species in high levels and trying to recover these effects with the aid of the antioxidant Trolox® was unsuccessful. Increasing levels of H2O2 may affect leaf pigmentation of WT microcuttings and auxin levels of both WT and sur1 microcuttings. Since the expression of auxin-responsive genes is decreased by H2O2 treatment via mitogen-activated protein kinase activation, microcuttings growth and rooting are impaired causing altered development pattern.

Inhibitory effects of Eucalyptus saligna leaf litter on grassland species: physical versus chemical factors

Abstract Background: In Southern Brazil, large areas of grassland have been replaced by Eucalyptus plantations. Vegetation is scarce under plantations which may be associated with Eucalyptus releasing of allelochemicals. Aims: To investigate effects of Eucalyptus saligna leaf litter on the colonisation and development of the ground layer by grassland species and if these effects were related to allelopathy. Methods: We assessed the effects of Eucalyptus litter on the establishment of species of the native grassland community and on seeded test species (Paspalum notatum and Lotus corniculatus – introduced). We tested the impact of the addition of E. saligna leaf litter, artificial leaves (shading and mechanical impediment) and shading. We also tested the phytotoxicity of the soil from E. saligna plantations. Results: Species richness, diversity, plant height, cover and biomass were lower in E. saligna leaves and artificial leaves treatments than in the control (absence of litter). The test species showed lower biomass and higher mortality in treatment plots with E. saligna leaves, artificial leaves and shading treatments than in the control. Allelochemicals did not accumulate in soil at phytotoxic levels. Conclusions: Eucalyptus saligna leaf litter suppresses the establishment of grassland vegetation, but the effects are mainly physical. Field evaluations with appropriate controls should be more extensively used in allelopathy investigations.

Antioxidant Evaluation of Baccharis patens and Baccharis psiadioides Essential Oils

Abstract The chemical composition of the essential oil of Baccharis patens Baker leaves was analyzed for the first time in the literature, by GC-MS and GC-FID. The antioxidant activity of B. patens and B. psiadioides (Less.) Joch. Müll. essential oils was determined by DPPH radical scavenging method. The oil was a complex mixture of terpenes, with 57 identified compounds. Sesquiterpene hydrocarbons were the main fraction (37.13%). Thymol, a standard antioxidant, showed 90% of antioxidant activity at 20 mg/mL. At a higher concentration, 100 mg/mL, B. patens and B. psiadioides essential oils resulted in 42% and 50% of antioxidant activity, respectively. Comparable antioxidant activity of the essential oils may be due to the similar low activity of their major compounds.

Phytotoxic effects of Baccharis psiadioides (Asteraceae) volatiles on different phases of plant development

Abstract Plants produce volatile compounds that can be phytotoxic. These compounds are present in the Asteraceae shrub Baccharis psiadioides Less. essential oil. Therefore, we assessed effects of B. psiadioides essential oil on several phases of Arabidopsis thaliana (L.) Heynh. life cycle. Essential oil chemical composition was verified by gas chromatography. Seeds and seedlings were exposed to volatiles in plates with agar medium whereas juveniles and adults were exposed inside glass chambers in soil. Oil chemical composition revealed monoterpene hydrocarbons as the most abundant chemical category and β-pinene was the major compound (44.65%). Germination and early growth were reduced by volatiles. Most evaluated parameters on juvenile and adult plants were not affected, but growth of juveniles decreased. We conclude that early phases of plant development were sensitive to the volatile’s exposure.

Nest site selection by Hypsiboas faber(Anura, Hylidae) in Southern Brazil

Male gladiator frogs of Hypsiboas Wagler, 1830 build nests on available substrate surrounding ponds and streams where female spawn eggs during the breeding period. Although gladiator frogs seem to show plasticity in the way they construct their nests, there is no study reporting if these species present preferences about microhabitat conditions for nest-building (mainly under subtropical climate). Predation pressure and environmental conditions have been considered major processes shaping the great diversity of reproductive strategies performed by amphibians, but microhabitat conditions should explain where to build a nest as well as how nest looks. This study aimed to test nest site selection for nest-building by Hypsiboas faber(Wied-Neuwied, 1821), determining which factors are related to nest site selection and nest features. The survey was conducted at margins of two permanent ponds in Southern Brazil. Habitat factors were evaluated in 18 plots with nest and 18 plots in the surrounding without nest (control), describing vegetation structure and heterogeneity, and substrate characteristics. Water temperature was measured inside the nest and in its adjacency. Nest features assessed were area, depth and temperature. Habitat characteristics differed between plots with and without nest. Microhabitat selected for nest-building was characterized by great vegetation cover and height, as well as shallower water and lower cover of organic matter in suspension than in plots without nest. Differences between temperature inside nest and in its adjacency were not observed. No relationship between nest features and habitat descriptors was evidenced. Results revealed that Hypsiboas faber does not build nests anywhere. Males seem to prefer more protected habitats, probably avoiding predation, invasion of conspecific males and inclement weather. Lack of differences between temperature inside- and outside-nest suggest that nest do not improve this condition for eggs and tadpole development. Nest architecture was not related to habitat characteristics, which may be determined by other factors, as nest checking by females before amplexus. Nest site selection should increase offspring survival as well the breeding success of Hypsiboas faber.