The evolutionary ecology of vegetative dormancy in mature herbaceous perennial plants

P>1. I present an evolutionary ecology interpretation of vegetative dormancy in mature herbaceous perennials. This kind of vegetative dormancy has been noted for at least 40 years, but has only recently become a topic of study. 2. Vegetative dormancy may be considered in a life-history context. Both vegetative dormancy and mortality typically decrease with increasing size. Vegetative dormancy's relationship to reproduction is more complex, because some species increase flowering and fruiting after dormancy while others do the opposite. 3. If vegetative dormancy is adaptive, then it is most likely a bet-hedging trait. Dormancy-prone plants are often long-lived, and in such organisms, bet-hedging traits should counter the effects of environmental stochasticity on adult survival. This adaptive context may vary by life span, because in shorter-lived plants, fitness is most sensitive to changes in reproduction rather than survival. 4. Vegetative dormancy could evolve if the costs of sprouting ever outweigh the benefits. The benefits of sprouting include: (i) photosynthesis and (ii) the opportunity to flower and reproduce. The costs include: (i) greater chance of herbivory, (ii) greater need for limiting nutrients, and (iii) greater maintenance costs. The many losses of photosynthesis among plants suggest that these benefits may not always outweigh the costs. 5. Vegetative dormancy may be an evolutionary step towards the loss of photosynthesis. Many non-photosynthetic plants acquire carbon from their mycorrhizal fungi. Many autotrophic, dormancy-prone plants also acquire some carbon from their mycorrhizal fungi. Further, non-photosynthetic plants often become dormant to an even greater extent than autotrophic, dormancy-prone plants. 6.Synthesis Vegetative dormancy often occurs in clades with non-photosynthetic, myco-heterotrophic plants, with implications for the evolution of traits involved in carbon nutrition. The links between vegetative dormancy, other life-history traits, mycorrhizas and the loss of photosynthesis should provide exciting directions for further research in plant evolutionary ecology. Particularly needed is an assessment of the physiology of vegetative dormancy, including whether the mycorrhiza is a carbon source in all dormancy-prone plant species. Equally important is a better understanding of the genetic relationships among photosynthesis, myco-heterotrophy and dormancy.