The effect of light and number of diurnal temperature fluctuations on germination of Phragmites australis

Abstract

Seed germination of the wetland emergent perennial Phragmites australis is stimulated by diurnally fluctuating temperatures. A germination experiment in darkness and light at different temperature regimes showed that P. australis germinated as well in darkness as in light over most of the temperature regimes tested. The germination requirements could partly explain why this species, despite a large annual production of small seeds, does not accumulate a persistent soil seed bank. A second experiment examined the effect of one to four diurnal temperature cycles with amplitude of fluctuations ranging from 0 to 30°C; diurnal mean temperature of 15°C. Germination in the absence of fluctuations was low, and logistic model estimates showed a positive effect of number of temperature cycles which was strongly influenced by amplitude size. For seeds that have fallen on moist ground during the winter, these laboratory results predict that a few large diurnal temperature fluctuations could be sufficient for onset of germination in the subsequently warmer spring period. Seeds that are located under water, however, are predicted to remain ungerminated until the water level falls. Hence, we suggest that the requirement for fluctuating temperature, in addition to being a sensor for 'exposed' seed sites, is also effectively acting as a germination timing mechanism.

Effect of temperature and salinity on germination ofRuta graveolensL.

“…Several authors have reported the importance of temperature during seed development and maturation as an important factor affecting seed germination (Allen & Meyer, 2002). Ekstam et al (1999) have elucidated the importance of fluctuating temperature as a requirement for germination and that in addition to being a sensor for ΄exposed΄ seed sites, it is also effective as a germination timing sensor. A slight increase or drop in temperature may affect a number of processes determining the germinability of seeds, including membrane permeability, activity of membrane-bound proteins and cytosol enzymes (Bewley & Black, 1994).…”

Response of littoral macrophytes to water level fluctuations in a storage reservoir

“…Available studies of seedling establishment of emergent macrophytes indicate that wet bare bottoms represent the best conditions, combining wet, but not flooded substrate, and light indicating space free of competition (Hejný and Husák, 1978;Weisner and Ekstam, 1993;Ekstam et al, 1999). Accordingly, the middle eulitoral with only a partial cover of perennial emergent macrophytes offers the best space for seedling establishment.…”

Efeito da temperatura e luz na germinação de sementes de Luetzelburgia auriculata (Alemão) Ducke - Fabaceae

“…Em geral, a alternância de temperatura é um mecanismo importante para aquelas espécies que não possuem sementes que germinam sob temperatura constante, revelando capacidade de adaptação e sucesso no estabelecimento, no ambiente que ocorrem (Ekstam et al 1999;Abdo & Paula 2006;Simão & Takaki 2008).…”

“…Para Abdo & Paula (2006), as temperaturas alternadas de 20-30 e de 25-35 °C favorecem o processo germinativo de sementes de Croton floribundus e não há germinação a 15, 20 e 40 C ou essa é mínima a 25 °C. Ekstam et al (1999) mostraram que sementes de Phragmites australis apresentaram alta porcentagem de germinação em temperaturas alternadas, na presença e ausência de luz.…”

“…Em Luetzelburgia auriculata, o fato de suas sementes germinarem em ampla faixa de temperatura, no claro e escuro, pode ser uma indicação que a espécie não mantém um permanente banco de sementes no solo e germinem tão logo lhes sejam oferecidos níveis adequados de umidade, de temperatura e de oxigênio. Para Ekstam et al (1999), a alta porcentagem de germinação de Phragmites australis, no claro e escuro, sugere explicar o fato dessa espécie, apesar da grande produção anual de pequenas sementes, não formar permanente banco de sementes no solo.…”