Visitors to the Botanic Garden in autumn are treated to a spectacular display of colour from the Liquidambar tree by the Lake, when the foliage floods deep wine-red in early autumn. This colour change marks the start of the process of leaf death. Allowing green leaves to fall would waste the nitrogen contained in the chlorophyll used to harvest the sun’s light. Instead, the plant stops making new chlorophyll and breaks down and reabsorbs any that exists. The red of the Liquidambar leaves is a result of the breakdown of sugars within the ageing leaf.
The process of leaf ageing is regulated by some of the elements of the circadian clock that regulate flower production. One part of this, the ‘evening complex’, maintains circadian rhythms and brings together signals from day length and temperature. As well as helping trigger flowering in spring as days lengthen and temperatures increase, it plays a part in triggering leaf death as autumn approaches.