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Germination traits are components of invasion potential, and comparing seed traits in sympatric native and invasive species can offer insights into the invasion process. We characterized seed germination traits and how they influenced the success of Eragrostis mexicana, a native species, and Eragrostis tenuifolia, an exotic species (Poaceae) in Mexico, in the context of their potential for biological invasion. Seeds from both species were collected from four sites in a natural protected area in Mexico City, and the germination of seeds of different ages was conducted in experiments at different temperatures. E. tenuifolia exhibited higher germination percentages than the native E. mexicana across all treatments. Seed age had differential effects, with older seeds of the native E. mexicana germinating better, while E. tenuifolia performed better with younger seeds. Temperature positively impacted germination for both species, although E. mexicana was limited at lower temperatures. Exotic E. tenuifolia can germinate over a wider temperature range with earlier germination rates, and generate a seed bank lasting several years, which may contribute to naturalization. The importance of germination traits in the context of invasive species establishment underscores the potential role of seed banks in facilitating biological invasions.

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El retamo espinoso (Ulex europaeus L.) es una planta introducida invasora de rápido crecimiento y diseminación, con producción de semillas, que permanecen latentes en los primeros 5 cm de profundidad del suelo; esta planta altera espacios ecológicos nativos, áreas de producción agropecuaria y su control y erradicación no es exitosa. Conocer ciertas características de las semillas del retamo facilitará su control. Así, el objetivo de este trabajo, fue determinar el vigor, la viabilidad y el banco de semillas de retamo espinoso, en zonas del páramo de Sumapaz. Para las pruebas, se colectaron semillas en tres sitios: Delicias, Usabá y Laguna. La prueba de vigor, se llevó a cabo mediante conductividad eléctrica y la de viabilidad, por ensayo topográfico de tetrazolio; en cada prueba, se realizó cuatro repeticiones, cada una con 100 semillas; el diseño estadístico fue completamente al azar. Para el banco de semillas, se tomaron muestras de suelo, a profundidades 0-5, 5-10 y 10-20 cm y se dispusieron en bandejas de aluminio. La prueba de vigor mostró que, después de 6 horas de hidratación, la cantidad de iones lixiviados se estabilizó, con un valor de 38,51 µs.cm -1 g-1, a las diez horas, afirmando alto vigor de semillas. La prueba de viabilidad presentó un 98 % y el banco de semillas registró mayor cantidad en el horizonte de 10-20 cm, con 950 semillas.m2, en la Laguna. Este estudio demuestra que las semillas de retamo tienen altos valores de vigor, viabilidad y un abundante banco de semillas distribuidas a diferentes profundidades.

The gorse (Ulex europaeus L.) is an invasive introduced plant of rapid growth and spread, with seeds production that remain dormant in the first 5 cm of soil depth, this plant alters native ecological spaces, areas of agricultural production, and its control and eradication is not successful. Know certain characteristics of gorse seeds will facilitate its control. Thus, the purpose of this work was to determine the vigor, viability and seed bank of gorse in areas of the Sumapaz paramo. For the tests, seeds were collected in three sites: Delicias, Usabá and Laguna. The vigor test was carried out by means of electrical conductivity and the viability test by tetrazolium topographic assay, in each test four repetitions were carried out, each with 100 seeds, the statistical design was completely random. For the seed bank, soil samples were taken at depths of 0-5, 5-10 and 10-20 cm, and placed in aluminium trays. The vigor test showed that after 6 hours of hydration, the amount of leached ions stabilized with a value of 38.51 µs.cm -1 g-1 at ten hours, confirming high seed vigor. The viability test presented 98 % and the seed bank registered a greater quantity in the 10-20 cm horizon with 950 seeds.m2 in the Laguna. This study shows that gorse seeds have high values of vigor, viability, and an abundant seed bank distributed at different depths.

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Understanding how the environment regulates seed-bank dormancy changes is essential for forecasting seedling emergence in actual and future climatic scenarios, and to interpret studies of dormancy mechanisms at physiological and molecular levels. Here, we used a population threshold modelling approach to analyse dormancy changes through variations in the thermal range permissive for germination in buried seeds of Arabidopsis thaliana Cvi, a winter annual ecotype. Results showed that changes in dormancy level were mainly associated with variations in the higher limit of the thermal range permissive for germination. Changes in this limit were positively related to soil temperature during dormancy release and induction, and could be predicted using thermal time. From this, we developed a temperature-driven simulation to predict the fraction of the seed bank able to germinate in a realistic global warming scenario that approximated seedling emergence timing. Simulations predicted, in accordance with seedling emergence observed in the field, an increase in the fraction of the seed bank able to emerge as a result of global warming. In addition, our results suggest that buried seeds perceive changes in the variability of the mean daily soil temperature as the signal to change between dormancy release and induction according to the seasons.

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The objective was to evaluate weed phytosociology and similarities between crop management systems in the Chapadões region. The experiment was conducted at in agricultural area located in the municipality of Chapadão do Sul, MS, during the 2016/17 harvest. Three crop managements strategies were used: (1) cotton/soybean/Urochloa, (2) millet/soybean/millet and (3) millet/soybean/crotalaria. A phytosociological survey of weeds was carried out during soybean cultivation and cover crops growth, in succession. The evaluation area for each management strategy was 0.5 ha. Soybean surveys were carried out in October and January, while the cover crop surveys were performed in February and May. The relative frequency (RF), relative density (RD), relative abundance (AR), and relative importance (RI) of weeds, Venn diagram, and Jaccard and Sorenson similarity indices were evaluated. The management area represented by the cotton/soybean/Urochloa rotation had fewer weed species than others. The species Cenchrus echinatus, Digitaria insularis, Digitaria sanguinalis, Eleusine indica and Commelina benghalensis had the highest phytosociological indeces among the monocotyledons. Attention is required for managing the dicotyledons Amaranthus deflexus, Conyza canadensis and Senna obtusifolia despite their low indices because of herbicide resistant cases. The highest indeces of similarity were found between managements areas 2 and 3, which did not rely on cotton cultivation prior to soybeans.

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Orchids need measures for conservation of their species, among them the creation of seed banks. This study analyzes suitable methodologies to identify the viability of Cattleya seeds through the tetrazolium test. Seeds of Cattleya nobilior Rchb. and Cattleya walkeriana Gardn. were submitted to three preconditioning: no soaking (control); sucrose (10%); or distilled water. After 24 hours, they were submitted to tetrazolium solution with three types of conditioning: oven (40 °C); water bath (40 °C); or room temperature. Subsequently, the percentage of viable seeds (VS) was calculated and in vitro sowing was carried out. Germination percentage (G) was determined after 45 days. A completely randomized design was used for each species studied, with treatments arranged in a 3x3 factorial scheme (three preconditioning and three conditioning), with eight replicates of one tube each. The experiment was performed in duplicate. The highest viability values found in the tetrazolium test were close to those of germination (C. nobilior: VS = 88% e G = 97%; C. walkeriana: VS = 88% e G = 95%) for Cattleya species native to the Cerrado. The conditioning at ambient temperature had a greater effect on seed visualization for both species studied, suggesting that the tetrazolium test should be performed at this conditioning temperature.(AU)

As orquídeas necessitam de medidas para a conservação de suas espécies, entre essas a criação de bancos de sementes. Objetivou-se identificar metodologia adequada para a identificação da viabilidade de sementes de Cattleya por meio do teste de tetrazólio. Sementes de Cattleya nobilior Rchb. e Cattleya walkeriana Gardn. foram submetidas a três pré-condicionamentos: sem embebição (controle); sacarose (10%) ou água destilada. Decorridas 24 horas, foram submetidas à solução de tetrazólio, com três tipos de condicionamento: estufa (40 °C), banho maria (40 °C) ou temperatura ambiente. Após esse período foi calculada a porcentagem de sementes viáveis (SV). Foi realizada a semeadura in vitro e, após 45 dias, determinada a porcentagem de germinação (G). Para cada espécie estudada, foi utilizado o delineamento inteiramente casualizado e os tratamentos foram arranjados em esquema fatorial 3x3 (três précondicionamentos e três condicionamentos) com oito repetições de um tubo de ensaio cada, sendo o experimento realizado em duplicata. Os maiores valores de viabilidade encontrados no teste de tetrazólio foram próximos aos de germinação (C. nobilior: SV = 88% e G = 97%; C. walkeriana: SV = 88% e G = 95%) para essas espécies de Cattleya nativas do Cerrado. Para as duas espécies estudadas, o condicionamento em temperatura ambiente apresentou melhor visualização das sementes, sugerindo que o teste de tetrazólio deve ser realizado nesta temperatura de condicionamento.(AU)

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Italian ryegrass (Lolium multiflorum Lam.) is a weed broadly found in fields cultivated with wheat and barley crops. Seed inputs into the soil before harvesting winter crops increase seed bank, ensuring survival. This study evaluated the persistence of Italian ryegrass seeds subjected to burial depths over time. Experiments were carried out in the field for two years in randomized block experimental design with four repetitions. Dormant seeds harvested from mother-plants were put in nylon bags containing soil. Previously, seed viability was evaluated in a 1 % tetrazolium solution, and 50 viable seeds by repetition were buried at 0.5, 5.0, 10, and 20 cm depths. Seed persistence was evaluated by the percentage of deteriorated and remaining seeds, non-dormant seeds, abnormal seedlings, and viable and non-viable dormant seeds at 0, 30, 60, 90, 180, 360, 540, and 720 days after burial (DAB). Seed persistence increased at 10 and 20 cm of burial depth compared to seeds in the soil layers up to 5 cm. Moreover, burial depth at 10 and 20 cm showed lower percentage of deteriorated seeds (10 % lower) compared to 0.5 cm at 360 DAB. For non-dormant seeds, a higher percentage was found at 90 DAB, regardless of seed burial depth. Dormancy breakage occurred until 180 DAB, and more rapidly at 10 and 20 cm depths. At 540 DAB, more than 95 % of seeds were unviable, demonstrating short persistence of Italian ryegrass in the soil seed bank.

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Italian ryegrass (Lolium multiflorum Lam.) is a weed broadly found in fields cultivated with wheat and barley crops. Seed inputs into the soil before harvesting winter crops increase seed bank, ensuring survival. This study evaluated the persistence of Italian ryegrass seeds subjected to burial depths over time. Experiments were carried out in the field for two years in randomized block experimental design with four repetitions. Dormant seeds harvested from mother-plants were put in nylon bags containing soil. Previously, seed viability was evaluated in a 1 % tetrazolium solution, and 50 viable seeds by repetition were buried at 0.5, 5.0, 10, and 20 cm depths. Seed persistence was evaluated by the percentage of deteriorated and remaining seeds, non-dormant seeds, abnormal seedlings, and viable and non-viable dormant seeds at 0, 30, 60, 90, 180, 360, 540, and 720 days after burial (DAB). Seed persistence increased at 10 and 20 cm of burial depth compared to seeds in the soil layers up to 5 cm. Moreover, burial depth at 10 and 20 cm showed lower percentage of deteriorated seeds (10 % lower) compared to 0.5 cm at 360 DAB. For non-dormant seeds, a higher percentage was found at 90 DAB, regardless of seed burial depth. Dormancy breakage occurred until 180 DAB, and more rapidly at 10 and 20 cm depths. At 540 DAB, more than 95 % of seeds were unviable, demonstrating short persistence of Italian ryegrass in the soil seed bank.(AU)

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BACKGROUND: Mexico is one of the most floristically rich countries in the world. Despite significant contributions made on the understanding of its unique flora, the knowledge on its diversity, geographic distribution and human uses, is still largely fragmented. Unfortunately, deforestation is heavily impacting this country and native tree species are under threat. The loss of trees has a direct impact on vital ecosystem services, affecting the natural capital of Mexico and people's livelihoods. Given the importance of trees in Mexico for many aspects of human well-being, it is critical to have a more complete understanding of their diversity, distribution, traditional uses and conservation status. We aimed to produce the most comprehensive database and catalogue on native trees of Mexico by filling those gaps, to support their in situ and ex situ conservation, promote their sustainable use, and inform reforestation and livelihoods programmes. METHODS: A database with all the tree species reported for Mexico was prepared by compiling information from herbaria and reviewing the available floras. Species names were reconciled and various specialised sources were used to extract additional species information, i.e. endemic status, threat status, availability in seed collections, reports on plant uses and conservation actions currently in place. With this information, a comprehensive catalogue of native trees from Mexico was redacted. Available georeferenced records were used to map each species distribution and perform spatial analyses to identify gaps of information and priority areas for their conservation and exploration. RESULTS: Mexico has at least 2,885 native tree species, belonging to 612 genera and 128 families. Fabaceae is the most represented family and Quercus the most represented genus. Approximately 44% of tree species are endemic to the country. The southern part of the country showed the highest values of species richness. Six hundred and seventy-four species have at least one documented human use. In terms of conservation assessment, ca. 33% of species have been assessed by either the IUCN Red List (919) or the National protection catalogue "NORMA Oficial Mexicana NOM-059" (29) or both (45). Additionally, 98 species have been included in the CITES listing for protection. In terms of existing conservation efforts, 19% of species have ex situ protection in seed banks, while protected areas overlap with all the identified peaks of species richness, except for those in the states of Veracruz and Chiapas. This work constitutes a key milestone for the knowledge, management, and conservation of the Mexican native trees. The two areas with high density of tree species identified in Veracruz and Chiapas represent two priority areas for tree conservation in Mexico, where integrated in situ and ex situ conservation efforts should be focused.

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RESUMEN Senecio vulgaris L. es una maleza, considerada de difícil control cuando se asocia a la zanahoria, debido a que compite por recursos con el cultivo, siendo importante su control, ya que tiene un impacto negativo en la productividad. La modelación biológica es una herramienta que permite prever los posibles efectos del control de la especie, ya que identifica las diferentes variables de un sistema y los factores que las afecta, para de este modo, predecir los resultados en diversos ambientes. Con base en la dinámica de sistemas y los aspectos morfo-fisiológicos de la especie, se planteó la modelación del banco de semillas de S. vulgaris, basado en las ecuaciones planteadas por Fernández-Quintanilla, donde se construyó el diagrama Forrester, al que se le incorporaron las diferentes ecuaciones y valores del modelo, para proyectar la dinámica de la especie en el banco de semillas, dependiendo del manejo. Se propusieron tres escenarios: (1) control con herbicidas en post-emergencia, (2) rotación de cultivos y (3) incorporar los métodos culturales de control, con un testigo en pre siembra y rotación de cultivos. Los resultados del modelo muestran que cuando se realiza rotación de cultivos y se incorporan manejos en pre-siembra al proceso convencional de la especie, se presenta una menor cantidad de semillas en el banco.

ABSTRACT Senecio vulgaris L. is a weed, considered difficult to control, when it is associated with carrot, because it competes for resources with the crop, its control being important, since it has a negative impact on crop productivity. Biological modeling is a tool that allows predicting the possible effects of the species control, since it identifies the different variables of a system and the factors that affect them, in order to predict the results in different environments. Based on the dynamics of systems and the morphophysiological aspects of the species, the modeling of the S. vulgaris seed bank was suggested, based on the equations proposed by Fernández-Quintanilla, the Forrester diagram was constructed, which was incorporated the different equations and values of the model, to project the dynamics of the species in the seed bank, depending on the management. Three scenarios were proposed, (1) post-emergence herbicide control, (2) crop rotation (3) incorporate traditional control methods with a control in presowing and crop rotation. The model results show that when crop rotation is performed and pre-sowing management is incorporated into the conventional process of the species, a smaller quantity of seeds is presented in the bank.

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Italian ryegrass (Lolium multiflorum L.) is an annual grass widely distributed in cultivated crops around the world. This weed causes significant yield reduction in many crops and has developed herbicide resistance. The aim of this study was to develop a cohort-based stochastic population dynamics model that integrates both emergence (thermal time) and dynamic population models as a tool to simulate the population dynamics of susceptible and resistant populations of L. multiflorum under the effects of climate change. The current climate scenario and the increase in the average air temperature by 2.5 °C were considered. Chemical and cultural management strategies commonly used in the South Region of Brazil during the winter and summer seasons were incorporated into the model. In the absence of control and under the current climate conditions, the seed bank population grew until reaching an equilibrium density of 19,121 ± 371 seeds m-2 for the susceptible and 20463 ± 363 seeds m-2 for the resistant populations. Considering the second climate scenario, the seed bank reaches an equilibrium density of 24,182 ± 253 seeds m-2 (+26% in relation to the current scenario) for the susceptible population and 24,299 ± 254 seeds m-2 (+18% in relation to the current scenario) for the resistant one. The results showed that the effect of the rise in temperature implies an increase in population in all the management strategies in relation to the current climate scenario. In both climate scenarios, the strategies based on herbicides application controlling cohorts 1 and 2 were the most efficient, and cropping systems including winter oat-soybeans rotation had a smaller impact on the L. multiflorum seed bank than crop rotations including winter wheat or summer corn. Crop rotations including wheat and corn for L. multiflorum management as an adaptive strategy under the future climate change are suggested.

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BACKGROUND: Consumers should show strong spatial preferences when foraging in environments where food availability is highly heterogeneous and predictable. Postdispersal granivores face this scenario in most arid areas, where soil seed bank abundance and composition associates persistently with vegetation structure at small scales (decimetres to metres). Those environmental features should be exploited as useful pre-harvest information, at least to avoid patches predicted to be poor. However, we did not find the expected spatial association in the algarrobal of the central Monte desert by observing foraging seed-eating birds, a field technique influenced by how much they exploit visited patches. In this work we tested if the first stage of foraging by granivorous birds (patch visit, encounter or exploration) is positively associated with environmental indicators of patch quality by recording the removal of single seeds from 300 scattered experimental devices during seasonal trials. Spatial selectivity was analysed by comparing the structural characteristics of used vs. available microhabitats, and evaluated against bottom-up and top-down hypotheses based on our previous knowledge on local seed bank abundance, composition and dynamics. Their foraging activity was also explored for spatial autocorrelation and environmental correlates at bigger scales. RESULTS: Postdispersal granivorous birds were less selective in their use of foraging space than expected if microhabitat appearance were providing them relevant information to guide their search for profitable foraging patches. No microhabitat type, as defined by their vegetation structure and soil cover, remained safe from bird exploration. Analyses at bigger temporal and spatial scales proved more important to describe heterogeneity in seed removal. CONCLUSIONS: Closeness to tall trees, probably related to bird territoriality and reproduction or to their perception of predation risk, seemed to determine a first level of habitat selection, constraining explorable space. Then, microhabitat openness (rather than seed abundance) exerted some positive influence on which patches were more frequently visited among those accessible. Selective patterns by birds at small scales were closer to our predictions of a top-down spatial effect, with seed consumption creating or strengthening (and not responding to) the spatial pattern and dynamics of the seed bank.

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Seeds of tropical pioneer trees have chemical and physical characteristics that determine their capacity to persist in the soil seed bank. These traits allow seeds to survive in the soil despite diverse predators and pathogens, and to germinate and recruit even decades after dispersal. Defenses in seedlings and adult plants often are described in terms of tradeoffs between chemical and physical defense, but the interplay of defensive strategies has been evaluated only rarely for seeds. Here we evaluated whether classes of seed defenses were negatively correlated across species (consistent with tradeoffs in defense strategies), or whether groups of traits formed associations across species (consistent with seed defense syndromes). Using 16 of the most common pioneer tree species in a neotropical lowland forest in Panama we investigated relationships among four physical traits (seed fracture resistance, seed coat thickness, seed permeability, and seed mass) and two chemical traits (number of phenolic compounds and phenolic peak area), and their association with seed persistence. In addition, seed toxicity was assessed with bioassays in which we evaluated the activity of seed extracts against representative fungal pathogens and a model invertebrate. We did not find univariate tradeoffs between chemical and physical defenses. Instead, we found that seed permeability - a trait that distinguishes physical dormancy from other dormancy types - was positively associated with chemical defense traits and negatively associated with physical defense traits. Using a linear discriminant analysis and a hierarchical cluster analysis we found evidence to distinguish three distinct seed defense syndromes that correspond directly with seed dormancy classes (i.e., quiescent, physical, and physiological). Our data suggest that short and long-term persistence of seeds can be achieved via two strategies: having permeable seeds that are well defended chemically, corresponding to the physiologically dormant defense syndrome; or having impermeable seeds that are well defended physically, corresponding to the physically dormant defense syndrome. In turn, transient seeds appear to have a lower degree of chemical and physical defenses, corresponding to the quiescent defense syndrome. Overall, we find that seed defense and seed dormancy are linked, suggesting that environmental pressures on seed persistence and for delayed germination can select for trait combinations defining distinct dormancy-defense syndromes.

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There is controversy over whether cactus species form soil seed banks. Although it is commonly assumed that cacti do not form seed banks, very few studies have evaluated them. In this work, we analysed whether cactus species form soil seed banks, studying seed distribution, seed density and seed longevity in the Southern Central Andes. Soil samples were collected in two microhabitats (under nurse plants and in bare areas) at 12 selected sites. We determined seed presence-absence, density and distribution for 32 native cactus species. Seed longevity for six of these species was determined through a burial experiment. We recorded viable seeds for 62.5% of the 32 evaluated species, finding variation in seed density between microenvironments and among populations. In some species, the highest seed density was found under potential nurse plants. Seed germination and seed viability decreased with burial time, with seed longevity always being <24 months after burial. Our results show strong evidence that cactus species do form seed banks. Seed density can vary between microenvironments and among populations, suggesting that cactus-nurse plant associations can also be explained by differential seed dispersal and not only by differential establishment. We found that Echinopsis and Gymnocalycium species form short-term seed banks. Our results will help to better understand the population dynamics of cactus species, a focal species group for conservation actions because many of them are threatened by human activities.

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Abstract Seed germination and seed longevity under different environmental conditions are fundamental to understand the ecological dynamics of a species, since they are decisive for its success within the ecosystem. Taking this into account, seed germination and seed storage behavior of a pioneer species of tropical dry forest (Tecoma stans) were studied in the laboratory, to establish the effect of different environmental conditions on a local tree population. Two seed lots collected in July 2011, from Cali (Colombia), were evaluated under three alternating temperatures (20/30, 20/25, 25/30 ºC; 16/8 h) and four light qualities (12-hour white light photoperiod, darkness, and 15 minutes of red light -R and far red light -FR). Final germination was recorded for all treatments; for white light treatment the daily germination was recorded to calculate mean germination rate, mean germination time, and two synchronization indices. To assess the effect of light quality on physiological variables, a destructive germination test was carried out. For this test, another seed lot was evaluated under the same light conditions using an alternating temperature of 20/30 °C - 16/8 h, recording germination during six days for every treatment. In addition, seeds were stored at two different moisture contents (7.7, 4.1 %) and three storage temperatures (20, 5, -20 ºC), during two time periods (one and three months); a seed germination test was conducted for each treatment. Four replicates of 35 seeds per treatment were used for all experiments. Germination was high (GP > 90 %) with all alternating temperatures under white light, whereas under R, FR, and darkness germination was evenly successful at low temperatures, but at higher temperature, half of the seeds entered into secondary dormancy (GP= 45-65 %). However, mean germination rate and synchronization under R and FR decreased significantly in comparison to white light treatment and, consequently, mean germination time increased. Seed storage behavior of this species is orthodox due to the high germination (GP > 90 %) obtained under all treatments. In conclusion, T. stans seeds have a negative germination response at high incubation temperatures in the absence of white light, entering into a secondary dormancy. In contrast, an environment with a lower temperature and without white light delays the germination, but at the end seeds are able to reach the same germination values. This seed dependence on incident light in limiting conditions suggests a physiological mechanism on the seed tissues of this species, probably mediated by phytochromes. Finally, the orthodox seed storage behavior of T. stans is a reason to include this species in ex situ seed conservation programs for restoration and recovery of the tropical dry forest; however, long-term studies should be conducted in order to evaluate the maintenance of this characteristic throughout longer periods of time. Rev. Biol. Trop. 66(2): 918936. Epub 2018 June 01.

Resumen La germinación y la longevidad de las semillas de una especie bajo diferentes condiciones ambientales son fundamentales para las dinámicas ecológicas de una especie, debido a que son decisivas en el éxito de la misma en un ecosistema. Teniendo en cuenta esto, se estudió la germinación y el comportamiento en el almacenamiento de las semillas de una especie pionera de bosque seco tropical (Tecoma stans) a nivel de laboratorio, para establecer el efecto de diferentes condiciones ambientales en una población local de árboles. Dos lotes de semillas recolectados en julio 2011, de Cali (Colombia), se evaluaron a tres temperaturas alternadas (20 / 30, 20 / 25, 25 / 30 °C; 16 / 8 h) y cuatro calidades de luz (fotoperiodo de 12 horas de luz blanca, oscuridad, y 15 minutos de luz roja -R y roja lejana -RL). Se registró la germinación final para todos los tratamientos; para el tratamiento de luz blanca se registró la germinación diaria para calcular la tasa media de germinación, el tiempo medio de germinación y dos índices de sincronización. Para evaluar el efecto de la calidad de luz sobre las variables fisiológicas, se realizó una prueba de germinación destructiva. Para esta prueba, otro lote de semillas fue puesto a las mismas condiciones de luz usando una temperatura alternada de 20 / 30 °C - 16 / 8 h, registrando la germinación durante seis días para cada tratamiento. Además, se almacenaron semillas a dos contenidos de humedad (7.7, 4.1 %) y a tres temperaturas de almacenamiento (20, 5, -20 °C), durante dos periodos de tiempo (uno y tres meses); se realizó una prueba de germinación a cada tratamiento. Cuatro repeticiones de 35 semillas por cada tratamiento se usaron en cada experimento. La germinación fue alta (PG > 90 %) en todas las temperaturas alternadas con luz blanca, mientras que en los tratamientos de luz R, RL y en oscuridad, la germinación fue igualmente exitosa a bajas temperaturas, pero a temperaturas más altas la mitad de las semillas entraron en latencia secundaria (PG= 45-65 %). Sin embargo, la tasa media de germinación y la sincronización en R y RL disminuyeron significativamente en comparación con el tratamiento de luz blanca y consecuentemente el tiempo medio de germinación aumentó. El comportamiento de las semillas de T. stans en el almacenamiento es ortodoxo debido a la alta germinación obtenida (PG > 90 %) en todos los tratamientos. En conclusión, las semillas de T. stans tienen una respuesta germinativa negativa a temperaturas de incubación alta en ausencia de luz blanca, donde entran a latencia secundaria. En contraste, un ambiente con baja temperatura y sin luz blanca retrasa la germinación, pero al final las semillas son capaces de alcanzar los mismos valores de germinación. Esta dependencia de las semillas a la luz incidente en condiciones limitantes sugiere la presencia de un mecanismo fisiológico en los tejidos de esta especie, probablemente mediado por fitocromos. Finalmente, el comportamiento ortodoxo de las semillas de T. stans en el almacenamiento abre la posibilidad de incluirla en programas de conservación ex situ para la restauración y recuperación del bosque seco tropical; no obstante, se deben llevarse a cabo pruebas más largas para evaluar el mantenimiento de esta característica por periodos de tiempo más largos.

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Dormancy cycles are an important mechanism for avoiding seed germination under unfavourable periods for seedling establishment. This mechanism has been scarcely studied in tropical species. Here, we studied three tropical and perennial species of Xyris, X. asperula, X. subsetigera and X. trachyphylla, to investigate in situ longevity and the existence of seasonal seed dormancy cycles. Seeds of three species of Xyris were buried in their natural habitat, with samples exhumed bimonthly for 18 months. Germination of exhumed seeds was assessed under a 12-h photoperiod over a broad range of temperatures. Seeds of X. trachyphylla were also subjected to treatments to overcome secondary dormancy. Seeds of all species are able to form a persistent seed bank and exhibit seasonal changes in germinability. Secondary dormancy was acquired during the rainy summer and was overcome during the subsequent dry season (autumn/winter). Desiccation partially overcomes secondary dormancy in X. trachyphylla seeds. Soil seed bank persistence and synchronisation of seed germination under favourable conditions for seedling establishment contribute to the persistence and regeneration of X. asperula, X. subsetigera and X. trachyphylla in their natural environment.

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The diaspore bank is an important component of biological diversity acting mainly as storage and source of diaspores, which also indicate dynamics and patterns of maintenance of plant diversity. We tested the hypothesis that the diaspore bank would be the responsible factor for the maintenance of the aquatic plant species, used two techniques to evaluate the diaspore bank: seedling emergence and direct counting of field samples. Density and richness of the diaspore bank were correlated with plant cover of the aquatic macrophyte communities and also with the euphotic zone radiation in different phases of the hydrological cycle. The diaspore bank is a key factor in maintenance of aquatic macrophyte assemblages in this pond. Nymphaea amazonum was one of the dominant species in the pond and presented temporally peaks of plant cover. Furthermore, depth allowed induction of germination of stored diaspores. Therefore, the diaspore bank may predict which species colonizes a site when environmental characteristics are favorable and allows inferring which processes are linked to changes in structure of aquatic macrophyte assemblages. These mechanisms are the means for recovery of macrophyte species under natural disturbances, represented by water level oscillations in floodplains.

O banco de diásporos é um componente importante da diversidade biológica atuando principalmente como armazenamento e fonte de diásporos, que também indicam a dinâmica e os padrões de manutenção da diversidade vegetal. Testamos a hipótese de que o banco de diásporos seria o fator responsável pela manutenção das espécies de plantas aquáticas, utilizando duas técnicas para avaliar o banco diásporo: emergência das plântulas e contagem direta de amostras de campo. Densidade e riqueza do banco de diásporos foram correlacionadas com cobertura vegetal das comunidades de macrófitas aquáticas e também com a radiação da zona eufótica em diferentes fases do ciclo hidrológico. O banco de diásporos é um fator chave na manutenção das assembleias de macrófitas aquáticas nesta lagoa. Nymphaea amazonum foi uma das espécies dominantes na lagoa temporalmente, apresentou picos de cobertura vegetal. Além disso, a profundidade permitiu a indução da germinação de diásporos armazenados. Portanto, o banco de diásporo é um preditor de quais espécies colonizarão um local quando as características ambientais são favoráveis e permite inferir que os processos estão ligados a mudanças na estrutura das assembleias de macrófitas aquáticas. Estes mecanismos são os meios para a recuperação de espécies de macrófitas sob as perturbações naturais, representados por oscilações do nível de água nas planícies aluviais.

Assuntos

RESUMO

This study aimed to assess the effects of sugarcane straw soil cover on Brachiaria plantaginea, Panicum maximum and Digitaria nuda seedlings emergence. The experiment was carried out in a soil classified as Red Nitosol. Seven different amounts of sugarcane straw soil cover were assessed (0, 3, 6, 9, 12, 15 and 18 ha-1). SP83-2847 variety straw was used. The experiment was arranged in a randomized blocks design, with four replications. Each experimental unit contained three species, which were allocated in the center of each plot, sown at 1 cm depth in a demarcated area. Different amounts of straw were distributed in this area. The sowing rate was used in order to obtain 1200 plant m-2. Two phases comprised the study. In the first phase, weeds emerged in sugarcane straw cover soil were assessed at 9, 12, 19, 34 and 43 days after sowing (DAS) and the second phase assessed plant emergence after straw removal, at 89, 130, 175, 196, 217 and 234 DAS. Seedlings that had over 1 cm shoot and were visible in all assessments were considered emerged. Soil cover sugarcane straw amount influenced the different species germination dynamics. In the first phase, species differential response was observed regarding used straw amount. In the second phase, after straw removal, there was higher germination for B. plantaginea and D. nuda, while P. maximum showed lower emergency, regardless of the used straw amount.

O presente estudo teve por objetivo avaliar os efeitos da cobertura do solo com palhiço de cana-deaçúcar sobre a emergência de Brachiaria plantaginea, Panicum maximum e Digitaria nuda. O experimento foi conduzido em um solo classificado como Nitossolo Vermelho. Foram avaliadas sete diferentes quantidades de coberturas do solo com palhiço de cana-de-açúcar (0, 3, 6, 9, 12, 15 e 18 t ha-1). Utilizou-se o palhiço da variedade SP83-2847. O delineamento experimental utilizado foi de blocos casualizados com quatro repetições. Cada unidade experimental continha as três espécies e foram alocadas na região central das parcelas, semeadas a 1 cm de profundidade em uma área demarcada, que posteriormente foram cobertas pelas diferentes quantidades de palhiço distribuídas uniformemente. A taxa de semeadura utilizada foi para obter-se 1.200 planta m-2. O estudo foi compreendido por duas fases. Na primeira fase foi avaliada a emergência das plantas daninhas sob cobertura de palhiço de cana aos 9, 12, 19, 34 e 43 dias após a semeadura (DAS) e a segunda, avaliou-se a emergência das plantas após a remoção do palhiço aos 89, 130, 175, 196, 217 e 234 DAS. Foram consideradas germinadas as plântulas visíveis em cada avaliação com mais de 1 cm de altura de parte aérea. A quantidade de palhiço de cana-de-açúcar utilizada como cobertura do solo influenciou a dinâmica de germinação das diferentes espécies. Na primeira fase observou-se uma resposta diferencial das espécies quanto a quantidade de palhiço utilizada. Na segunda fase, após a remoção do palhiço, verificou-se maior germinação para B. plantaginea e D. nuda, enquanto P. maximum apresentou menor emergência, independente da quantidade de palhiço utilizada.

Assuntos

RESUMO

The diaspore bank is an important component of biological diversity acting mainly as storage and source of diaspores, which also indicate dynamics and patterns of maintenance of plant diversity. We tested the hypothesis that the diaspore bank would be the responsible factor for the maintenance of the aquatic plant species, used two techniques to evaluate the diaspore bank: seedling emergence and direct counting of field samples. Density and richness of the diaspore bank were correlated with plant cover of the aquatic macrophyte communities and also with the euphotic zone radiation in different phases of the hydrological cycle. The diaspore bank is a key factor in maintenance of aquatic macrophyte assemblages in this pond. Nymphaea amazonum was one of the dominant species in the pond and presented temporally peaks of plant cover. Furthermore, depth allowed induction of germination of stored diaspores. Therefore, the diaspore bank may predict which species colonizes a site when environmental characteristics are favorable and allows inferring which processes are linked to changes in structure of aquatic macrophyte assemblages. These mechanisms are the means for recovery of macrophyte species under natural disturbances, represented by water level oscillations in floodplains.(AU)

O banco de diásporos é um componente importante da diversidade biológica atuando principalmente como armazenamento e fonte de diásporos, que também indicam a dinâmica e os padrões de manutenção da diversidade vegetal. Testamos a hipótese de que o banco de diásporos seria o fator responsável pela manutenção das espécies de plantas aquáticas, utilizando duas técnicas para avaliar o banco diásporo: emergência das plântulas e contagem direta de amostras de campo. Densidade e riqueza do banco de diásporos foram correlacionadas com cobertura vegetal das comunidades de macrófitas aquáticas e também com a radiação da zona eufótica em diferentes fases do ciclo hidrológico. O banco de diásporos é um fator chave na manutenção das assembleias de macrófitas aquáticas nesta lagoa. Nymphaea amazonum foi uma das espécies dominantes na lagoa temporalmente, apresentou picos de cobertura vegetal. Além disso, a profundidade permitiu a indução da germinação de diásporos armazenados. Portanto, o banco de diásporo é um preditor de quais espécies colonizarão um local quando as características ambientais são favoráveis e permite inferir que os processos estão ligados a mudanças na estrutura das assembleias de macrófitas aquáticas. Estes mecanismos são os meios para a recuperação de espécies de macrófitas sob as perturbações naturais, representados por oscilações do nível de água nas planícies aluviais.(AU)

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RESUMO

Uma alternativa para conservação de espécies é um banco de sementes, onde é possível conservar e propagar estas plantas, porém para isto é necessário se ter uma noção da qualidade das sementes estocadas. Uma alternativa é utilizar testes de vigor, entre eles a deterioração controlada. O objetivo deste trabalho foi avaliar o efeito da deterioração controlada sobre sementes de orquídeas e determinar qual o tempo de exposição destas a este tipo de tratamento. Sementes de Cattleya schilleriana, C. tigrina, C. crispata e C. labiata foram submetidas à deterioração de zero a 48h a 43°C. Para sementes de C. crispata não foi encontrado um período adequado para o teste de deterioração controlada. Recomenda-se para as sementes de C. tigrina, C. labiata e C. schilleriana a utilização de 27 h a 43°C, todavia variáveis como o tempo e a temperatura ainda precisam ser melhores estabelecidos para este grupo de plantas. O teste de tetrazólio não foi eficiente para avaliar a qualidade das sementes após a deterioração controlada.

An alternative for conservation of this species is seed banking, based in that is possible to make conservation and propagations of the endangered species. But for this the seed quality must be monitored. Vigour tests can offer an option, and one of this is the controlled deterioration, which expose the seeds with high moisture to high temperatures during a determined period of time. The present work aimed to evaluate the controlled deterioration test over four orchid species in different times. Seeds of C. schilleriana, C. tigrina, C. crispata and C. labiata was submitted to deterioration from times ranging from zero to 48h at 43°C. For Cattleya crispata it was not found a effective time for the test. did not suffer any deterioration at any time. It is recommended for C. tigrina, C. labiata and C. schilleriana the use of 27 h at 43°C. However, time and temperature should be better studied for this group of plants. Tetrazolium test was not efficient to evaluate the seed quality after controlled deterioration.

Assuntos

RESUMO

Uma alternativa para conservação de espécies é um banco de sementes, onde é possível conservar e propagar estas plantas, porém para isto é necessário se ter uma noção da qualidade das sementes estocadas. Uma alternativa é utilizar testes de vigor, entre eles a deterioração controlada. O objetivo deste trabalho foi avaliar o efeito da deterioração controlada sobre sementes de orquídeas e determinar qual o tempo de exposição destas a este tipo de tratamento. Sementes de Cattleya schilleriana, C. tigrina, C. crispata e C. labiata foram submetidas à deterioração de zero a 48h a 43°C. Para sementes de C. crispata não foi encontrado um período adequado para o teste de deterioração controlada. Recomenda-se para as sementes de C. tigrina, C. labiata e C. schilleriana a utilização de 27 h a 43°C, todavia variáveis como o tempo e a temperatura ainda precisam ser melhores estabelecidos para este grupo de plantas. O teste de tetrazólio não foi eficiente para avaliar a qualidade das sementes após a deterioração controlada.(AU)

An alternative for conservation of this species is seed banking, based in that is possible to make conservation and propagations of the endangered species. But for this the seed quality must be monitored. Vigour tests can offer an option, and one of this is the controlled deterioration, which expose the seeds with high moisture to high temperatures during a determined period of time. The present work aimed to evaluate the controlled deterioration test over four orchid species in different times. Seeds of C. schilleriana, C. tigrina, C. crispata and C. labiata was submitted to deterioration from times ranging from zero to 48h at 43°C. For Cattleya crispata it was not found a effective time for the test. did not suffer any deterioration at any time. It is recommended for C. tigrina, C. labiata and C. schilleriana the use of 27 h at 43°C. However, time and temperature should be better studied for this group of plants. Tetrazolium test was not efficient to evaluate the seed quality after controlled deterioration.(AU)

Assuntos