Desynchronization and re‐synchronization of reproduction by Astragalus scaphoides, a plant that flowers in alternate years

Abstract

Mast seeding, the synchronous seed production by plants at irregular intervals, has been widely studied from the perspective of its fitness benefits, but much less is known about the proximate factors that cause plants to reproduce synchronously. In this article, I follow up on more than two decades of research investigating proximate mechanisms of mast seeding by Astragalus scaphoides, an iteroparous perennial forb. We use longterm monitoring in relation to two environmental manipulations to evaluate the importance of exogenous environmental factors versus endogenous feedbacks for synchrony in this species. Our past research showed that synchrony in this species is explained by the pollencoupling hypothesis: plants that flower synchronously set seed and deplete stored resources, whereas plants that happen to flower asynchronously are pollen limited, set fewer seeds, and do not deplete resources, and flower again until they are resynchronized. Continued monitoring of two experimental manipulations, water addition, and flower removal, provides additional support for this model, and also reveals subtle effects of water availability on synchrony. Water addition decreased flowering, rather than increasing it as expected based on simple correlations with weather variables, suggesting that precipitation does not synchronize reproduction. Exogenous drivers are generally considered to be the primary synchronizing factors in plant reproduction. Our work in this system suggests that endogenous feedbacks may be more important than has been previously assumed.

Disentangling the effects of feedback structure and climate on Poaceae annual airborne pollen fluctuations and the possible consequences of climate change

“…Although most aerobiological literature (Aboulaich et al, 2009(Aboulaich et al, , 2013Cariñanos et al, 2014;García-Mozo et al, 2009) establishes exogenous factors as being exclusive drivers when explaining pollen dynamics, our results suggest that the endogenous feedback structure of the system should also be considered in order to fully understand pollen fluctuations. This is supported by Jato et al (2009), who concluded that weather-related factors alone are insufficient in accounting for Poaceae pollen fluctuations and Crone (2013), who suggested that endogenous processes may also be more important for Poaceae pollen dynamics than previously assumed, due to the impact of the intrinsic growth rhythm on flowering time.…”

“…However, empirical evidence shows that longterm Poaceae airborne pollen fluctuations are fairly stable with respect to a trend (or, if not a trend, to its persistent state) and do not deviate or drift away unbounded (García-Mozo et al, 2010a). Therefore, airborne pollen fluctuations could be the consequence of negative feedback mechanisms (internal or endogenous processes), able to persist over time in a state of dynamic equilibrium with their environment (Crone, 2013;Ferrero et al, 2014;Hernández Plaza et al, 2012;Jato et al, 2009;Lima et al, 2012). Understanding how both feedback structure and exogenous factors interact in shaping the dynamic of populations is fundamental to our ability to manage and predict ecosystem response under climate change.…”

Seed production and predation in a changing climate: new roles for resource and seed predator feedback?

“…Similar experiences of different time spans implying different roles for endo‐ and exogenous processes are provided by Schauber et al. () and Crone (), although evidence from long‐term data with food web interactions are still largely lacking (Pearse et al. ).…”

“…Whereas various combinations of weather effects and resource feedback mechanisms seem to be common among masting plants (Selås , Crone , Kelly et al. , Crone and Rapp , Pearse et al.…”

“…). Seed fluctuation patterns may, furthermore, depend on how plants allocate resources over time (Selås , Crone , Kelly et al. , Miyazaki , Crone and Rapp , Pearse et al.…”