Synchrony in fall leaf drop: chlorophyll degradation, color change, and abscission layer formation in three temperate deciduous tree species.

PREMISE OF THE STUDY: Deciduous tree species remove some nutrients from their leaves during fall leaf senescence through retranslocation. Retranslocation impacts the timeline of leaf fall, amount of active chlorophyll, and overall leaf nitrogen content as fall color change occurs. Our objective was to identify interspecific differences in the timing of abscission layer formation, leaf color change, and the level of chlorophyll degradation of young trees during fall senescence.

METHODS: Leaf relative chlorophyll content for three tree species was measured during fall 2015 by a greenness meter. These measurements were calibrated for each species through spectrophotometric determination of leaf chlorophyll concentration. Abscission layer formation was tracked using light microscopy of sampled leaves. Excised leaves were photographed on a flat white surface to track species leaf color through time.

KEY RESULTS: All three species had different chlorophyll declination rates throughout the fall season. The maple species started with less chlorophyll and began abscission layer formation earlier. The other two species had a similar starting chlorophyll level and onset timing of abscission layer formation. Visible leaf color change was not associated with a threshold in either chlorophyll degradation or abscission layer formation across species.

CONCLUSIONS: Maple species degraded less chlorophyll on average, in the fall, than did the oak and beech species. The rate of chlorophyll degradation in coordination with abscission layer formation varied by species. Color change was not a good predictor of level of chlorophyll degradation in leaves across species.