Hormones and shifting ecology throughout plant development

Hormones modulate complex suites of ecologically relevant behaviors through interactive cascades of signal transduction; evolutionary changes in the function of a single hormone can result in multiple changes in plant traits. Sites of hormone action and tissue sensitivity change throughout plant ontogeny, as embryos, seedlings, and reproductively mature plants cope with shifting suites of environmental variables and resource availability. Phenotypic plasticity and correlations and trade‐offs between life history traits (such as resource use efficiency and allocation to growth and differentiation of meristems) also change as plants age; hormonal changes are central to these shifts. I synthesize evidence from the molecular and physiology literature and present novel data on mangrove propagules, seedlings, saplings, and trees. Together, these data demonstrate that several ecologically important traits are hormonally mediated (both in the short term and over evolutionary time) in the diversification of plant lineages. I focus on two hormones with contrasting action: (1) abscisic acid (ABA), which regulates internal plant osmotic stability, membrane integrity, seed dormancy, and stomatal conductance; and (2) cytokinins (zeatin and allied adenine derivatives), which promote cell division, stimulate growth, delay leaf senescence, enhance the capacity of tissues to act as N sinks, and help to transduce signals of light and nutrient availability. ABA and cytokinin levels are correlated with patterns of osmotic tolerance, photosynthesis, growth, and leaf longevity, and their concentrations in specific tissues change throughout plant development. Ecologists and evolutionary biologists are in a strong position now to creatively comprehend, predict, and potentially engineer plant strategies and adaptive trade‐offs over plant lifetimes in light of emerging knowledge of hormones.