RESUMO
KEY MESSAGE: Through a multidisciplinary study we found that Gymnocalycium bruchii, an endemic cactus from central Argentina, acts as a dioecious species, which is the first record in this genus. Cactaceae species are typically hermaphroditic; however, about 2% have other different reproductive systems. These non-hermaphroditic species may develop sexual dimorphism in flowers or other reproductive, vegetative or ecological traits, besides a specific breeding system and floral ontogeny. Therefore, multidisciplinary research is necessary to fully understand reproduction in those species. For this purpose, we studied Gymnocalicium bruchii, a globose cactus endemic to central Argentina that is presumably dioecious or gynodioecious. We made observations in two natural and two cultivated populations. We made morphological observations of plants and flowers, and performed quantitative analyses to determine the sex ratio, size of plants and flowers, flower production, fruiting, among other variables. We performed hand-pollination, self-fertilization and free-pollination tests to determine the breeding system. Finally, we studied the anatomy and ontogeny of the reproductive organs using permanent histological slides of flower morphs at different stages. Our results confirm that Gymnocalicium bruchii is a dioecious species. Female flowers have atrophied anthers and a functional gynoecium that produces fruits and seeds. Male flowers are bigger and have a functional androecium but a sterile gynoecium. In the cultivated population, the sex ratio was 1/1, whereas the number of male individuals was higher in both natural populations. Pollination tests corroborated dioecy. Ontogenetic studies revealed that in female flowers the anthers collapse before microspore maturation, while in male flowers the gynoecium shows normal development of the ovary, style, stigma, and ovules; however, the latter are never fertilized.
RESUMO
Woody species composition in invaded communities from mountains of central Argentina: their relations with local environmental factors. Invasions by exotic woody species are threatening ecosystem functions worldwide. The spread and subsequent replacement of native forest by exotic dominated stands is particularly evident nearby urban centers were exotic propagule pressure is highest. Yet, there is a lack of information on the environmental factors that underlie these replacements. In this study we addressed the following questions: (1) is there a local spatial segregation between the dominant native and exotic woody species? and (2) if this local segregation does exist, is it driven by environmental features?. For this, in 2010 we established 31 plots distributed along 16 sampling sites where we surveyed the composition and abundance of all woody species with a basal diameter ≥ 5cm. To characterize the environment of each plot, we measured the topographic position (slope, exposure) and different properties such as soil physics (bulk density, soil impedance), structure (soil deep, texture) and chemical characteristics (pH, nutrient and water content). Through a cluster analysis we were able to identify five different woody communities in coexistence: (1) Woodlands dominated by the exotic Ligustrum lucidum; (2) Mixed woodlands dominated by the native Lithraea molleoides and the exotic Celtis australis; (3) Scrublands dominated by the native Condalia buxifolia; (4) Scrublands dominated by the exotic Cotoneaster glaucophyllus, and (5) Scrubby grasslands with the exotic Pyracantha angustifolia. These communities were all associated with different local topographic and edaphic features. The environmental segregation among the identified communities suggests that woody invaders have the potential to colonize almost all the environments of the study site (though varying in the identity of the dominant exotic species). The observed patterns, even being restricted to a single well invaded area of mountain Chaco, may posit the spread of woody invaders towards native communities in the region.
En todo el mundo, las invasiones de especies leñosas exóticas están amenazando las funciones ecosistémicas. La dispersión y el subsecuente reemplazo de bosques de especies nativas por comunidades dominadas por exóticas es evidente, particularmente, en proximidad a centros urbanos donde la presión de propágulos de especies exóticas es alta. Sin embargo, existe una falta de información sobre los factores ambientales que subyacen este reemplazo. En este estudio nos propusimos responder las siguientes preguntas: (1) ¿se observa una segregación espacial a escala local entre especies leñosas exóticas y/o nativas dominantes?, y (2) si existe esa segregación, ¿está asociada a variables ambientales? En el 2010 se establecieron 31 parcelas distribuidas en 16 laderas en los bosques Chaqueños de las Sierras de Córdoba, en Argentina central. En cada uno de los sitios de muestreo se relevó la composición y abundancia de todas las especies leñosas con un diámetro a la altura de la base superior a 5cm. Para caracterizar el ambiente en cada una de las parcelas medimos la posición topográfica (pendiente y orientación) y algunas propiedades asociadas con la física (densidad aparente y compactación), estructura (profundidad y textura) y con la química (pH y el contenido de nutrientes y agua) del suelo. A través, de un análisis jerárquico de agrupamiento, se identificaron cinco comunidades de leñosas coexistiendo: (1) Bosques dominados por Ligustrum lucidum, (2) Bosques mixtos dominados por Lithraea molleoides y Celtis australis, (3) Matorrales de Condalia buxifolia, (4) Matorrales de Cotoneaster glaucophyllus, y (5) Pajonales con emergentes de Pyracantha angustifolia. Estas comunidades se asociaron diferencialmente a las variables topográficas y edáficas locales. La segregación ambiental observada sugiere que las especies invasoras tienen una capacidad potencial para colonizar casi todos los ambientes en el área de estudio (variando la identidad de la invasora). En conjunto, los patrones descritos, aunque circunscriptos a un área de Chaco Serrano con un avanzado grado de invasión, plantearían un escenario de posible expansión de las leñosas exóticas sobre las comunidades nativas.
Assuntos
Ecossistema , Florestas , Espécies Introduzidas , Madeira/crescimento & desenvolvimento , ArgentinaRESUMO
Invasions by exotic woody species are threatening ecosystem functions worldwide. The spread and subsequent replacement of native forest by exotic dominated stands is particularly evident nearby urban centers were exotic propagule pressure is highest. Yet, there is a lack of information on the environmental factors that underlie these replacements. In this study we addressed the following questions: (1) is there a local spatial segregation between the dominant native and exotic woody species? and (2) if this local segregation does exist, is it driven by environmental features? For this, in 2010 we established 31 plots distributed along 16 sampling sites where we surveyed the composition and abundance of all woody species with a basal diameter ≥ 5 cm. To characterize the environment of each plot, we measured the topographic position (slope, exposure) and different properties such as soil physics (bulk density, soil impedance), structure (soil deep, texture) and chemical characteristics (pH, nutrient and water content). Through a cluster analysis we were able to identify five different woody communities in coexistence: (1) Woodlands dominated by the exotic Ligustrum lucidum; (2) Mixed woodlands dominated by the native Lithraea molleoides and the exotic Celtis australis; (3) Scrublands dominated by the native Condalia buxifolia; (4) Scrublands dominated by the exotic Cotoneaster glaucophyllus, and (5) Scrubby grasslands with the exotic Pyracantha angustifolia. These communities were all associated with different local topographic and edaphic features. The environmental segregation among the identified communities suggests that woody invaders have the potential to colonize almost all the environments of the study site (though varying in the identity of the dominant exotic species). The observed patterns, even being restricted to a single well invaded area of mountain Chaco, may posit the spread of woody invaders towards native communities in the region.
Assuntos
Ecossistema , Florestas , Espécies Introduzidas , Madeira/crescimento & desenvolvimento , ArgentinaRESUMO
Worldwide decomposition rates depend both on climate and the legacy of plant functional traits as litter quality. To quantify the degree to which functional differentiation among species affects their litter decomposition rates, we brought together leaf trait and litter mass loss data for 818 species from 66 decomposition experiments on six continents. We show that: (i) the magnitude of species-driven differences is much larger than previously thought and greater than climate-driven variation; (ii) the decomposability of a species' litter is consistently correlated with that species' ecological strategy within different ecosystems globally, representing a new connection between whole plant carbon strategy and biogeochemical cycling. This connection between plant strategies and decomposability is crucial for both understanding vegetation-soil feedbacks, and for improving forecasts of the global carbon cycle.
