Germination behaviour of the seeds of six New Zealand woody plant species

Open Access
Publisher Website
Google Scholar
Abstract
Germination rates, percentage germination success, and phenomena related to germination delay were determined for one provenance each of seeds from freshly-collected fruit (summer-autumn) of Dodonaea viscosa, Hedycarya arborea, Pennantia corymbosa, Pseudowintera colorata, Rhopalostylis sapida, and Streblus heterophyllus. Dodonaea has wind-dispersed fruit; the fruit of the others are eaten by birds which disperse the seeds. The experimental treatments simulated natural conditions that the seeds might experience after dispersal. In the standard treatment (seeds cleaned, moist, well-lit) each species behaved differently. Streblus seeds began to germinate a few weeks after the start of the experiment and germination continued at a gradual, even rate through the winter. Hedycarya seeds began to germinate within three months and underwent a germination flush in mid-winter, then a levelling off before the last few seeds germinated in spring. A few Dodonaea seeds germinated in autumn and a few more in late winter. There was a slight flush in spring-early summer and slower germination in later summer. A halt in autumn was followed by germination of a few more seeds in late autumn and the last few in the following spring. A few Pennantia seeds germinated in winter, but the main flush and completion of germination was in the next spring. Pseudowintera seeds began to germinate in winter, then the rate levelled off in spring, and halted in summer. Germination was completed in the following winter. Rhopalostylis seeds germinated in the summer following the start of the experiment. Percentage germination success in the standard treatment was high (95–100%) for all species. An impermeable seed coat is part of the germination delay system for Dodonaea; and impermeability is overcome at different rates within a seed cohort. Fleshy pericarp tissues inhibit seed germination completely for Streblus and Pseudowintera, almost completely for Hedycarya and Rhopalostylis, and to a considerable degree for Pennantia. Immature embryos or primary dormancy (interacting with temperature) with delays distributed to different degrees among individuals of a cohort, may be responsible for slow germination rates of seeds with the pericarp removed. Environmental constraint (requirement for relatively high temperature) is likely to be involved with the Rhopalostylis germination pattern. In the dark treatment most seeds germinated for all species except Rhopalostylis, which failed completely, probably because of fungal attack. In a later experiment most Rhopalostylis seeds also germinated in the dark. Pseudowintera seeds germinated faster in the dark than in the light. All species except Rhopalostylis germinated relatively well on soil. The specific germination patterns allow the emergence of seedlings to be well spread through time; at least some will benefit from environmentally favourable periods. Although seed germination behaviour for these species is compatible with what is known of the regeneration ecology and habitat preferences of the respective species, it does not explain them completely.