Making a clean break: contrasting leaf abscission dynamics across temperate leaf habits

Area of Science:

• Plant physiology
• Ecology
• Forest science

Background:

• Leaf abscission is a regulated process of leaf shedding at the abscission zone (AZ).
• Leaf senescence, a nutrient reclamation phase, often precedes abscission but their timing varies.
• Physiological regulation of leaf abscission in trees is poorly understood, influenced by environmental and endogenous signals.

Purpose of the Study:

• To investigate the roles of water status, gas exchange, senescence, and abscisic acid (ABA) in regulating leaf abscission.
• To characterize the physiological diversity in leaf abscission processes across different temperate tree types.

Main Methods:

• Developed a novel method to quantify abscission zone competency (AZC).
• Measured leaf gas exchange, chlorophyll content, water potential, AZC, and ABA levels in four temperate tree species.
• Assessed associations between physiological traits and AZC throughout the season.

Main Results:

• Deciduous species exhibited contrasting patterns: one senesced before AZC, the other photosynthesized until AZC.
• Brevi-deciduous species showed gradual AZC with significant chlorophyll degradation.
• Marcescent species' leaves senesced but did not develop AZC.

Conclusions:

• Leaf senescence and abscission are distinct and variably timed processes in temperate trees.
• Physiological diversity in leaf abscission regulation is significant and understudied.
• Findings have implications for predicting leaf lifespan under changing climate conditions.