Fruit dispersal and seed banks in Atriplex sagittata : the role of heterocarpy

Summary1 Atriplex sagittata , an arly succesional, annual species of disturbed habitats in Central Europe, produces three types of fruits. We studied the differences in dispersal between the fruit types in order to investigate their ecological roles. 2 The typical positive relationship between dispersal ability and germinability is not found in this species. Type A (ebracteate) fruits produced deeply dormant seeds and had the lowest dispersal potential, but of the two fruits with bracts, type B, with dormant seeds, was better dispersed by both water and wind than type C, which produces non‐dormant seeds. 3 Wind, temperature and precipitation have significant effects on fruit release but their effects differ between fruit types. The release of fruit types with bracts was positively correlated with wind whereas all fruit types tended to be negatively correlated with precipitation and temperature range. 4 Type C fruit, which contains non‐dormant seed, are absent from the soil in summer and have a Type II transient seed bank. Type A and B fruits, containing dormant seeds, form a persistent seed bank. 5 Heterocarpy, where fruit types show distinct ecological behaviour, enables colonizing species such as A. sagittata to survive both major disturbance (by ensuring that some seeds persist) and unfavourable conditions (by spreading germination over a long period). 6 In A. sagittata , seed dynamics can be explained by the germination behaviour of seeds produced by the three types of fruit. All fruit types mature in autumn, but few of Type A fall from the mother plant until spring, when germination is probably inhibited because of insufficient stratification. Type C fruit, however, show peak dispersal in winter and the majority of these non‐dormant seeds are able to germinate as soon as conditions become more suitable.