Germination patterns of six herbs invading the Chinese subtropics

Germination is a key step driving biological invasions. We evaluated germination patterns of six herbaceous  species  that  commonly  invade  natural  and  agricultural  regions  of  China.  Seed  fresh mass, shape, and water absorption were measured, and germination was tested under alternating day/night  temperature  regimes  and  light/dark  treatments.  Seeds  of  Amaranthus  hybridus  were physiologically dormant, exhibiting a low germination percentage (<20 %) under all treatments. Maximum germination of all other study species ranged from 56 % to 95 % in the light-exposed treatments,   but   optimal   temperature   requirement   was   species   specific.   For instance,   Bidens frondosa seeds  germination  rate  was  highest  (70  %)  in  warm  treatments (25/35  and  35/40  ◦C), while the rate for Dysphania ambrosioides was highest (>90 %) in cold treatments (10/20 and 20/30  ◦C).  Germination  of  the  small-seeded  Crassocephalum  crepidioides  and  D.  ambrosioides was reliant  on  light  exposure,  with  nearly  null  germination  in  the  dark.  Seed morpho-physical  traits may influence germination patterns of invasive herbs in Chinese landscapes. Observed dormancy may  be  related  to  seed  after-ripening  (or  cold  stratification)  rather than  the  incubation  temper- ature regimes, as could be the case of A. hybridus. Nevertheless, for most species the temperature regimes  are  key  drivers  of  germination  timing,  determining  the  season  of  recruitment,  enabling vasive  species  to  avoid  competition  and  to  colonize and  coexist  in  similar  habitats rldwide.