Fernando Biganzoli

Macro-Climatic Distribution Limits Show Both Niche Expansion and Niche Specialization among C4 Panicoids.

Grasses are ancestrally tropical understory species whose current dominance in warm open habitats is linked to the evolution of C4 photosynthesis. C4 grasses maintain high rates of photosynthesis in warm and water stressed environments, and the syndrome is considered to induce niche shifts into these habitats while adaptation to cold ones may be compromised. Global biogeographic analyses of C4 grasses have, however, concentrated on diversity patterns, while paying little attention to distributional limits. Using phylogenetic contrast analyses, we compared macro-climatic distribution limits among ~1300 grasses from the subfamily Panicoideae, which includes 4/5 of the known photosynthetic transitions in grasses. We explored whether evolution of C4 photosynthesis correlates with niche expansions, niche changes, or stasis at subfamily level and within the two tribes Paniceae and Paspaleae. We compared the climatic extremes of growing season temperatures, aridity, and mean temperatures of the coldest months. We found support for all the known biogeographic distribution patterns of C4 species, these patterns were, however, formed both by niche expansion and niche changes. The only ubiquitous response to a change in the photosynthetic pathway within Panicoideae was a niche expansion of the C4 species into regions with higher growing season temperatures, but without a withdrawal from the inherited climate niche. Other patterns varied among the tribes, as macro-climatic niche evolution in the American tribe Paspaleae differed from the pattern supported in the globally distributed tribe Paniceae and at family level.

Dormancy and germination responses of kiwifruit (Actinidia deliciosa) seeds to environmental cues

Seed germination of the kiwifruit (Actinidia deliciosa A. Chev. C.F. Liang and A.R. Ferguson), a deciduous, perennial vine, is low because of seed dormancy. The main purpose of this study was to characterize kiwifruit seed dormancy and germination in response to environmental factors such as temperature and light. Dormancy of hydrated seeds is alleviated by the perception of a period at low temperatures (stratification) of at least 3 weeks at 2 or 5°C. Alleviation of dormancy is accomplished by incubation at fluctuating temperatures (20/30°C). A red light pulse did not affect germination, whereas a far-red light pulse strongly inhibited germination. This inhibition was readily reverted by a second pulse of red light, indicating that phytochromes are also involved in dormancy alleviation. Although seed germination was inhibited by the fruit pulp, the latter prevented neither perception of low temperature nor changes in the light sensitivity of the seeds. Therefore, it can be advanced that kiwifruit seeds will only germinate after dispersal if the time–temperature requirement for dormancy alleviation and fluctuating temperatures for dormancy termination are fulfilled. Perception of a closed canopy might interfere with dormancy termination.

Análisis de diversidad de la familia Poaceae en la región austral de America del Sur

Resumen Analisis de diversidad de la familia Poaceae en la region austral de America del Sur. La familia Poaceae es una de las mejor representadas en America del Sur austral, con un total de 206 generos que comprenden 1523 especies distribuidas en 10 subfamilias diferentes. En este trabajo analizamos la distribucion de estos grupos en Argentina, sur de Brasil (Parana, Rio Grande do Sul y Santa Catarina), Chile, Paraguay y Uruguay; discutimos la riqueza de las diferentes subfamilias, tribus y generos, su distribucion, especies endemicas, la relacion de especies anuales y perennes, asi como el numero de especies Kranz y no Kranz, su abundancia segun regiones geograficas, en relacion con la temperatura y las precipitaciones, generos disyuntos, y la proporcion de taxones en relacion con las diferentes. Abstract Analysis of Poaceae biodiversity in austral South America. The Poaceae is one of the best represented families in austral South America with a total of 206 genera comprising 1523 species arranged in 10 different subfamilies. Here we analyzed the distribution of these taxa in Argentina, southern Brazil (Parana, Rio Grande do Sul and Santa Catarina), Chile, Paraguay, and Uruguay; we discuss the species richness of the different subfamilies, tribes and genera, its distribution, endemics, annual and perennial species as well as Kranz and non Kranz taxa, its geographical distribution in relation to temperature and rainfall, disjunct genera, and proportion of taxa in relation to the different ecoregions in the area.