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

Background and Aims: Leaf senescence allows plants to reallocate nutrients from aging leaves, often storing them for future use. As chlorophyll breaks down, other pigments emerge, creating the vibrant colors of autumn. In many deciduous trees, senescence is followed by abscission the physical detachment of leaves at the abscission zone (AZ). Though closely linked, senescence and abscission are distinct; some plants senesce without abscising, while others abscise partially senesced leaves. Most research on these processes has focused on herbaceous and crop species, which do not naturally shed leaves. Methods: To better understand how leaf senescence and abscission occur in temperate deciduous trees, we developed a novel method to quantify AZ competency (AZC) we also measured gas exchange, chlorophyll content, water potential, and abscisic acid in four tree species representing deciduous, brevi-deciduous, and marcescent leaf habits. Key results: The two deciduous species showed contrasting patterns: one degraded chlorophyll and ceased photosynthesis before AZC developed; the other retained chlorophyll and continued photosynthesis until nearly all AZs became competent. The brevi-deciduous species lost most chlorophyll but developed AZs gradually over a longer period. The marcescent species fully senesced but did not develop AZC. Conclusions: These findings show that senescence and abscission are distinct and variably timed processes across temperate tree species.