El bosque del escarpe occidental del rio Parana (Argentina): composicion floristica y estructura

El borde occidental de la llanura aluvial del río Paraná en Argentina presenta un pronunciado escarpe que no es superado por las crecientes. Su vegetación en un bosque subtropical semideciduo de linaje paranaense-amazónico, dominado por Holocalyx balansae, Ficus luschnathiana, Patagonula americana, Gleditsia amorphoides y otras. Se analizaron seis stands de este bosque empleando el método de los cuadrantes de Cottam y Curtis. Los resultados del relevamiento se exponen aquí, suministrando frecuencia, densidad y dominancia relativas, el valor de importancia de cada especie, junto con la descripción estructural del bosque. Se discute su composición florística comparada con la de bosques semejantes em otras áreas de Argentina y Brasil.<br>The western limit of the alluvial plains of the river Parana in Argentina presents a pronounced scarp, above the level of floodings. The vegetation, a semideciduos subtropical forest of Amazonian origin, was analyzed using the point-centred quarter method. The parameters relative frequency, relative density, relative dominance and importance value index for each species are provided, together with a brief structural description. The floristic composition is compared with similar forests elsewhere in Argentina and Brazil

Photosynthetic pathway variation among C4 grasses along a precipitation gradient in Argentina

Aim Based on the biochemical and physiological attributes of C4 grasses, and on the close association between decarboxylation pathways and the taxa in which they evolved, the hypotheses tested were: (1) that C4 grasses would become progressively more abundant as precipitation decreased, with grasses of the NADP-me subtype more abundant in wetter sites and those of the NAD-me subtype more common in arid regions; and (2) that the distribution of grass subfamilies would also be correlated with annual precipitation. Location The study was conducted along a precipitation gradient in central Argentina, from the eastern Pampas (>1000 mm year)1 ) to the western deserts and semi-deserts near the Andes (<100 mm year)1 ). Methods Percentage of species and relative cover of C3 and C4 grasses (including C4 subtypes) in local floras from 15 lowland sites of central Argentina were obtained from our own unpublished data and from recently published floristic surveys. Pearson correlation coefficients were obtained between grass distribution parameters and the available climatic data. Results The percentage of C4 grasses increased towards the arid extreme and showed a strong negative correlation with annual rainfall (r = )0.74, P < 0.01). Within the C4 subtypes, the NADP-me species showed a higher proportional representation at the wetter extreme, whereas the representation of NAD-me species increased towards the more arid extreme. The relationship of PEP-ck species with climatic parameters in central Argentina was less evident. The distributions of the Panicoideae and Chloridoideae subfamilies along the precipitation gradient were diametrically opposed, with the Panicoideae positively (r = 0.86, P < 0.001) and the Chloridoideae negatively (r = )0.87, P < 0.001) correlated with annual precipitation. Main conclusions Our data are consistent with the broad observation that C4 grasses tend to dominate in areas where the wet season falls in the warmer summer months. In agreement with previously reported results for Africa, Asia, Australia and North America, we describe here for the first time a significant relationship between annual precipitation and the prevalence of the NADP-me and NAD-me photosynthetic pathways along climatic gradients for the Neotropics. We also report for the first time that correlations between C4 species and annual rainfall are stronger when the relative cover of grass species is considered. The association of grass subfamilies Panicoideae and Chloridoideae with rainfall is as strong as that recorded for the NADP-me and NAD-me variants, respectively, suggesting that characteristics other than decarboxylation type may be responsible for the geographic patterns described in this studyFil: Cabido, Marcelo Ruben. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Pons, Stella Maris. Universidad Nacional de Córdoba. Facultad de Ciencias Agropecuarias; ArgentinaFil: Cantarero, Juan Jose. Universidad Nacional de Río Cuarto. Facultad de Agronomía y Veterinaria; ArgentinaFil: Lewis, Juan Pablo. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Anton, Ana Maria Ramona. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentin