There’s nothing like autumn in New York! If you’re like us, it’s fun and awe-inspiring to know there’s a chain reaction of molecular biology behind this season’s gorgeous color palate. Nature’s Rube Goldberg machine starts with the sun when daylight triggers leaves to produce chlorophyll, giving them their green color. As fall sets in, a reduction in sunlight means a reduction in chlorophyll, and dominant greens give way to yellow and orange pigments—made of flavonoids and carotenoids—that exist in the leaf all along, but are less dominant than chlorophyll’s coloring. What about seasonal reds and purples? Those are the colors of anthocyanin (which we think sounds like our new favorite hair metal band). Anthocyanin production is triggered when an excess of sugars made in the leaf by day are blocked from circulating out of the leaf by night, as the leaf’s veins gradually seal off and prepare to fall in response to cooler temps. Autumn of warm, sunny days (lots of light) with cooler, drier nights (but not too cold) elongates this process of sugary buildup. While yellow and orange pigments stay pretty consistent each fall, the production of anthocyanin, and therefore the flourish of red pigments, varies based on annual temperature and moisture conditions. These variables also influence the timing and duration of the changing of the leaves—which means each autumn is like a snowflake!
