Intra-population seed survival during burial on a mass basis

Abstract

Survival during burial is dependent upon a seed's ability to resist pathogen pressure and physiological aging. Several studies support a positive interspecific relationship between seed survival in soil and seed coat thickness. Our research attempted to understand if a similar intraspecific relationship occurs in Rudbeckia mollis (Asteraceae) seeds of different mass. Seeds were collected in August 2016 and separated into light (383 ± 7 µg), intermediate (409 ± 8 µg), and heavy (447 ± 10 µg) mass classes. Pericarp thickness was measured on fresh sections of seeds from each class. Seeds were buried 25 cm deep in a non-irrigated wildflower plot and monitored for viability with a standard germination test over 24 months. Final germination percentage varied from 0 to 98% with an overall mean of 82 ± 30% among all mass classes. Germination percentage and germination rate correlated positively with soil temperature suggesting dormancy cycling that is consistent with non-deep physiological dormancy. There was no consistent relationship between the likelihood of germination and seed mass but heavy class seeds were more likely to be recovered intact following burial. Pericarp thickness ranged from 24.7–41.4 µm and there was a weak positive relationship with mass. This research suggests no short-term relationship between intra-population seed mass and viability loss during burial. However, thicker seed coats in higher mass seeds may confer greater resistance to pathogen pressure. This research is supportive of a positive intra-population relationship between survival in soil and seed coat thickness.