Effects of temperature, light and stratification on seed germination of Wollemi pine (Wollemia nobilis, Araucariaceae)

Abstract

Wollemia nobilis W.G.Jones, K.D.Hill D J.M.Allen isrepresented in the wild by about 40 adult trees; therefore, understanding therequirements for seed germination is important for the conservation of thismonotypic Australian conifer. Constant-temperature experiments found that seedgermination proceeded most rapidly at temperatures between 24 and 30˚C.Few seeds germinated when incubated for 112 days at 10 and 16˚C but latergerminated when transferred to 24˚C, whereas seeds initially incubated at35˚C were killed. Unstratified seeds showed a pattern of prolongedgermination taking 130 days to achieve 40% germination at 24˚C and40 days at 27˚C. Seeds stratified at 6˚C for 14 days and incubatedat 27˚C in the light achieved 40% germination within 20 days whilethose incubated at 10 and 16˚C for 112 days and transferred to 24˚Cachieved 40% germination by 15 and 24 days, respectively. Initialgermination of unstratified seeds was fastest when incubated at 30˚C inthe light, averaging 23 days. Exposure to 12-h diurnal periods of 10–15mol m^–2 s^–1 lightsignificantly increased 28-dayincubation germination percentages, but for onlythose incubated at 30˚C. Additions of gibberellic acid(GA₃) at 1 mM had no effect on seed germination ofW. nobilis. The field observations and laboratoryexperiments indicate that following seed shed in summer and early autumn whentemperatures are high, W. nobilis seeds germinate,especially if exposed to light. The seeds that remain ungerminated or that areshed late in the season survive over winter, but germinate rapidly oncetemperatures rise in the next spring.