Germinação de sementes de Drymaria cordata (L.) Willd. ex Roem & Schult.: efeito do potencial hídrico

Abstract

-(Germination of Drymaria cordata (L.) Willd. ex Roem & Schult. seeds: effect of water potential). Mathematical models based on thermal time (degree day) and hydrotime (O w day) can be used as an input to more general models of seed germination and seedling emergence in the field, and may be an important tool for understanding weed biology and control. Germination of Drymaria cordata seeds in response to reduced water potentials in the medium was evaluated by using the hydrotime model. Both the germinability and germination rate decreased linearly with the reduction of the water potential (O w ), attaining values near a zero at -0.8 MPa. The rate of decrease was higher at optimum temperature as compared to suband supra-optimum temperatures. The mean base water potential (O wb ) was similar between sub-(19 °C) and supra-optimum (32 °C) temperatures, and was higher (less negative) at optimum temperature (25 °C), showing that D. cordata seeds are less sensitive to reduced water potential at 19 °C than at 25 °C. Hydrotime was higher for seeds germinated at sub-optimum than at optimum temperature, showing that the germination rate for a given water potential is higher at optimum temperature. The hydrotime required for seeds to complete germination was higher at supra-optimum than at optimum temperature, and lower at supra-optimum than at sub-optimum temperature. In general, hydrotime was relatively constant among subpopulations. The hydrotime model can well describe the effects of water potential on the time-course of seed germination of D. cordata, particularly at sub-and supra-optimum temperatures.Key words -hydrotime, modelling, temperature, weeds RESUMO -(Germinação de sementes de Drymaria cordata (L.) Willd. ex Roem & Schult.: efeito do potencial hídrico). Modelos matemáticos baseados no conceito de graus dia ("thermal-time") e O w dia ("hydrotime") podem ser usados para a elaboração de modelos mais gerais sobre a germinação e emergência de plântulas no campo, podendo ser uma importante ferramenta para estudos sobre a biologia de plantas daninhas e seu controle. Neste trabalho, avaliou-se a germinação de sementes de D. cordata em resposta ao potencial hídrico (O w ), usando-se o modelo O w dia. Tanto a germinabilidade como a velocidade de germinação decresceram linearmente com a redução do O w , atingindo valores próximos a zero em -0.8 MPa. Em temperatura ótima, a taxa de queda na germinação foi maior em comparação com as temperaturas sub-e supra-ótima. O O w base (O wb ) mediano foi similar entre as temperaturas sub-ótima (19 °C) e supra-ótima (32 °C), mas foi maior (menos negativo) à temperatura ótima (25 °C), mostrando que sementes de D. cordata são menos sensíveis à redução do potencial hídrico à 19 °C do que à 25 °C. O O w dia foi maior para sementes germinadas à temperatura sub-ótima do que à temperatura ótima, mostrando que a velocidade de germinação num dado potencial hídrico é maior em temperatura ótima. A quantidade de O w dia necessária para a germinação foi maior em temperatura supra-ótima ...

Effect of reduced water potential on seed germination of a forest tree: a hydrotime approach

“…Concerning native species, few studies in current literature investigated such threshold models regarding water relations and seed germination of tropical trees (Daws et al, 2008). Some studies evaluated the role of Ψ on seed germination of Brazilian species (Botelho and Perez, 2001;Fonseca and Perez, 2003;Rego et al, 2007), but rarely explaining whether germination would fit the presupposes of hydrotime models (Cardoso and Pereira, 2008;Oliveira et al, 2019). Most attention regards to the role of temperature, rather than water potential, as described by thermal time models in neotropical species (Cardoso and Pereira, 2009;Pires et al, 2009;Daibes and Cardoso, 2018;Duarte et al, 2018).…”