Resumo Foi estudada a dinâmica do crescimento dos caules aéreos de Paspalum vaginatum, uma gramínea de ampla distribuição. Com o objetivo de identificar características diferenciais quantitativas entre dois genótipos, as plantas foram cultivadas ao ar livre em vasos durante dois verões consecutivos. Os eixos de diferentes ramificações foram marcados para observação periódica para quantificar a taxa de produção de entrenós, taxa de crescimento do eixo principal, taxa de cobertura e esforço reprodutivo. Os genótipos diferiram significativamente nas seguintes características quantitativas: proporção de eixos plagiotrópicos vs. ortotrópicos, taxa de produção de entrenós, proporção de eixos reprodutivos vs. vegetativos, cobertura vegetal e distribuição espacial do canópia. O conhecimento dessas características pode ajudar a compreender a grande plasticidade e adaptabilidade desta espécie a múltiplas condições ambientais.
Abstract The aerial growth dynamics of the shoots of the widespread turfgrass Paspalum vaginatum was studied. With the aim of identifying quantitative differential features between two genotypes, plants were cultivated outdoors in pots during two consecutive summers. Axes of different branching order were marked for periodical observation to quantify internode production rate, axis production rate, covering rate and reproductive effort. The genotypes differed significantly in the following quantitative features: plagiotropic vs. orthotropic axes proportion, internode production rate, flowering vs. vegetative tiller ratio, vegetative cover and spatial distribution of the canopy. Knowledge of these features may help to understand the great plasticity and adaptability of this species to multiple environmental conditions.
Morphological and physiological responses to freezing were evaluated in two ecotypes of the perennial turfgrass Paspalum vaginatum. Leaf extension rate, number of active meristems, leaf water potential and net photosynthesis were measured on plants of both a commercial cultivar, 'Sea Isle 2000', and a wild ecotype from the Flooding Pampa grasslands of Argentina. Plants were propagated by cloning, cultivated in pots, and examined during 18 consecutive days under two treatments: a non-frozen control treatment (15.5±7 ºC) and a frozen treatment with two stages: Stage 1 with four hours of freezing stress for 10 nights (-5ºC), and Stage 2 with 12 hours of freezing stress for eight nights (five nights at -5ºC and three nights at -8ºC). After these treatments, plants were returned to the outside environment to evaluate shoot injury and post-freezing recovery. Leaf water potential, net photosynthesis and leaf extension rate were significantly higher in the wild ecotype than in the commercial cultivar. Meristem density was reduced after freezing in both ecotypes, but was more pronounced in the commercial cultivar (98.5%) than in the wild ecotype (80%). Thus, the two ecotypes coming from different environments, exhibited different morphological and physiological responses to exposure to freezing temperatures.