Serotiny as a reproductive strategy in the specially protected species Ariocarpus kotschoubeyanus (Cactaceae)

Plant species with aerial seed banks are commonly referred to as "serotinous," an adaptation in which seed release happens in response to an environmental trigger. Individuals of Ariocarpus kotschoubeyanus (Cactaceae), a specially protected species, store some seeds on the plant over 1 year. We examined the seed retention time, the release mechanism, and the germination behavior of this species in Central Mexico. Flowers produced in a population of A. kotschoubeyanus were monitored, and the number of fruits retained or expelled was determined to calculate the serotiny degree (the number of seeds retained in the tubercules of the plant divided by the total number of seeds produced per plant). The seed retention in previous years was estimated for 30 individuals. The dynamics of retained seeds in the mother plant (seed age in "rings") were determined from the annual average production of tubercules per individual, using observations for 5 years. A germination test employing the seeds collected from recently formed fruits and those obtained from different rings was conducted. We observed that 86.6% of the plants showed seed retention (aerial seed bank) in some ring of the aerial stems. The serotiny degree was 37.3, having 32.68 seeds per plant. Seeds retained in the "rings" from 1- to 24-year-old plants had a higher germination proportion (between 0.40 and 0.73) than fresh seeds (0.13). Seeds increase their germination proportion with age; thus, seed retention by tubercules (serotiny) represents a reproductive strategy to conserve germplasm until favorable conditions to germinate are present.