Seed dormancy revisited: Dormancy‐release pathways and environmental interactions

Abstract Many internal (inherent) and environmental (imposed) factors control seed dormancy and germination that we divide into three basic dormancy‐release pathways: Maternal structures and embryo physiology control inherent dormancy that is broken by various types of scarification and physiological changes, followed by imposed‐dormancy release when the prevailing environment is replaced by certain ‘standard’ conditions that stimulate germination (Pathway 1); imposed dormancy prevails even if inherent dormancy is broken or not applicable that is released when replaced by certain ‘standard’ environmental conditions which stimulate germination (Pathway 2); and release from inherent dormancy by light/dark or cold stratification is contingent on the pre‐existence of certain environmental conditions that stimulate germination (Pathway 3). On‐plant seed storage (serotiny) and frugivorous seeds are recognized here as representing special types of physical dormancy, as their properties are consistent with those of hard diaspores. Warm stratification does not require seeds to be moist as it is just a physical response. Heat may promote germination of non‐hard, as well as hard, seeds as it may increase their permeability further. Levels of germination gauge the net effect of inherent‐ and imposed‐dormancy release so that it is only possible to identify the extent of inherent‐dormancy release when conditions for germination are optimal (imposed dormancy has been annulled). While imposed dormancy may be protracted after inherent dormancy is broken by heat or chilling during the dry or cold seasons, release from both states may effectively coincide if smoke chemicals or light are received during the (wet) growing season. We suggest reserving the term secondary dormancy for seeds that return to (inherent or imposed) dormancy due to changed environmental conditions. Under seasonal climates, fluctuations in environmental conditions can lead to secondary dormancy and even dormancy cycling. We recognize four types of functional interactions between any two environmental factors that induce inherent‐dormancy release: binary interactions are ineffective, only one stimulus is effective, both are effective but non‐additive, or both are additive/synergistic. Two environmental stimuli that individually break dormancy but have no additive effect must be affecting the same process; this was demonstrated here for some interactions between heat and smoke. The three dormancy‐release pathways, together with internal, seasonal and stochastic interactions, are coordinated by the non‐dormant seed to ensure maximum germination under optimal conditions. To ignore any aspect outlined here leads to an impoverished understanding of the disparate seed ecology of species adapted to different stressful and disturbance‐prone habitats. Read the free Plain Language Summary for this article on the Journal blog.