Endogenous Influences on Leaf Longevity

The normal value of leaf longevity for a species reflects functional relationships at the foliar and whole-plant level, but longevity can be both prolonged and shortened by environmental conditions. From first principles, leaf longevity is expected to increase in environments where critical resources are scarce. This generalization is rooted in a cost–benefit analysis of leaf longevity arguing that the nature of leaves in resource-limited environments imposes a long payback period on the cost of their construction (Chabot and Hicks 1982; Kikuzawa 1991). In this view, selection pressure is expected to act to prolong leaf longevity in light-, water-, or nutrient-limited environments. This expectation is consistent with observations among species and plants in differing resource environments, but not within individual plants. The expectation applies to conditions of resource limitation, not stress conditions that near or exceed the limits to a species’ survival and reproduction. Stress events such as deep drought, unseasonal frost and freezing, lengthy flooding, salinity, air pollutants, and attack by herbivores or pathogens each impose qualitatively different challenges to leaf function (Kozlowski and Pallardy 2002), which we also address in this chapter.