T he biological zero and accumulated temperature for seed germination of six Asteraceae species in eastern Guangdong
Temperature is an important environmental factor influencing on seed germination of plants . In this study , we use the thermal time model to analyze accumulated temperature and biological zero for seed germination of six Asteraceae species including Conyza canadensis , Synedrella nodiflora , Praxelis clematidea , Spilanthes paniculata , Bidens pilosa , A geratum conyzoides incubated five temperatures (15 ,20 ,25 ,30 ,35 and 40 ℃) . The result shows that the seed of six Asteraceae species display a 80% ~95% germination at the optimum temperature range , exception with C canadensis (52 ~ 55% ) . The optimum temperature range for germination of C canadensis and P clematidea is 20~25 ℃ , and that of the other species is from 15 to 30 ℃ , and to 35 ℃ , or to 40 ℃ , that of S nodi f lora seed is from 25 to 40℃ .Biological zero for germination of C canadensis native to north America , and B pilosa widely distribution in world is the lower (3.94 and 5.48 ℃ , respectively ) , and that of S nodi f lora , P clematidea , A conyzoides is higher (16.90 ,12.56 and 11.12 ℃ , respectively ) . There is a significant positive correlation between biological zero and mean annual low temperature of native habitat of species ,and a significant negative correlation between biological zero and accumulated temperature for germination (P<0.05) . Exception with S . nodiflora , the population of the other five Asteraceae species may have stronger expansion potential to high latitude zone .
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