The effects of light quality, nitrate concentration and presence of bracteoles on germination of different fruit types in the heterocarpous Atriplex sagittata

1 We investigated the effect of light quality, nitrogen supply, fruit size and age on germination of the three types of fruit produced by Atriplex sagittata. 2 Regardless of fruit type, seed germination was significantly reduced in the dark. Light quality had no significant effect on germination of seeds from fruit types A and B, both of which are dormant, but seeds from fruit type C, which are non-dormant, germinated better in green light (low photon flux and red : far-red ratio, simulating conditions in the canopy) than in white light. 3 Optimum nitrate concentration differed between seed types but, for all, germination was reduced at the highest concentration used. 4 The effects of cold stratification and its interaction with light and nitrogen effects were also studied. Strong interactions between stratification and light were found in all seed types but other interactions were less frequent. 5 Three size classes of type C fruit showed similar final germination percentages but large seeds germinated more slowly. 6 The effect of seed age was highly significant: over a 3 year period, the germinability of dormant seeds (types A + B) increased while that of non-dormant seeds (type C) fell. 7 The salt concentration in bracteoles of freshly ripened fruits was too low to mediate an inhibitory effect on germination. Moreover, the first autumn rain would be sufficient to remove all the salt from bracteoles. 8 Differences between fruit types in depth of dormancy, and in response to the quality of light and to nitrate concentration in the soil, allows A. sagittata to respond to the spatial and temporal variation in environmental conditions encountered by this annual of disturbed habitats.