Speaker 1: Welcome to brainstuft, a production of iHeart Radio, Hey, brain Stuff,
Speaker 1: Flour and vog obam here enthusiastic snowball fights in winter
Speaker 1: or blazy summer days at the beach. Notwithstanding, autumn might
Speaker 1: be the most beloved season of the mall. Every year,
Speaker 1: people in temperate climates watch in awe as the trees
Speaker 1: begin their magical transformation from green powerhouses to veritable Morgese
Speaker 1: boards of brilliant yellows, fiery oranges, and vibrant reds. It's
Speaker 1: even a tourist attraction. The northeastern United States, for example,
Speaker 1: hosts millions of leaf peepers from all over the world
Speaker 1: who come to observe nature's fine art gallery. Myths about
Speaker 1: why this occurs stretch back through time, from the hot
Speaker 1: and O'shannee to the Algonquin to the Wye Dot. A
Speaker 1: few Native American people's legends feature a wayward bear, sometimes
Speaker 1: represented by ursa Major or the Big Dipper, which returns
Speaker 1: to the sky every autumn. The legends say that the
Speaker 1: bear was injured in a hunt or a fight, and
Speaker 1: that's blood tends the leaves red each year. Much more recently,
Speaker 1: researchers have sussed out the science behind these transformations, involving
Speaker 1: photosynthesis and pigments. For a large part of the year,
Speaker 1: leaves are a tree's workhorses, constantly converting carbon dioxide, water,
Speaker 1: and sunlight into energy in the process called photosynthesis. The
Speaker 1: key to this process is the pigment chlorophyll, which is
Speaker 1: what gives leaves their green color for much of the year.
Speaker 1: But while chlorophyll is the star of the show, it
Speaker 1: has some help in the form of other pigments like
Speaker 1: caroteene and xanthophill. Xanto is Greek for yellow, and Caroteene
Speaker 1: is named for carrots because it's what gives them and
Speaker 1: other things their orange color. These two pigments are always
Speaker 1: present in leaves and help absorb sunlight, which they transfer
Speaker 1: to chlorophyll for photosynthesis to occur. As summer nears its
Speaker 1: end and days get shorter, the decreased amount of sunlight
Speaker 1: incites trees to prepare for a sort of hibernation. The
Speaker 1: leaves won't be able to continue photosynthesizing during winter due
Speaker 1: to the dry air and lack of light, so the
Speaker 1: tree does two things. First, it forms a separation layer
Speaker 1: made of cork like cells at the base of each leaf,
Speaker 1: to seal it off from the tree the second it
Speaker 1: stops producing chlorophyll, since it won't need this pigment until
Speaker 1: the days start to Lengthen once again in the spring,
Speaker 1: with chlorophyll out of the picture, the yellow and orange
Speaker 1: pigments get a chance to shine. The red hues which
Speaker 1: come from pigments called anthocyanins, are slightly more complicated. Whereas
Speaker 1: all trees contain chlorophyll, carotene, and xanthophill, and not all
Speaker 1: of them produce anthocyanins, even the ones that do have
Speaker 1: anti synons only produce it under certain conditions. Remember that
Speaker 1: layer of cork like cells at the base of the leaf.
Speaker 1: Its purpose is to protect the tree during the colder winter,
Speaker 1: conserving energy and preventing the tree from drying out. And
Speaker 1: when the separation layer is complete, the leaves fall off
Speaker 1: of the tree. But before the leaves fall off and
Speaker 1: the tree closes up shop, it wants to pull in
Speaker 1: as much sugar and nutrients as possible from its leaves,
Speaker 1: which is where the antisyonin comes into play. Although scientists
Speaker 1: offer several different possible reasons for why some trees produce anthocyanins,
Speaker 1: the prevailing theory is that these pigments protect the leaves
Speaker 1: from excess sunlight and enable the trees to recover any
Speaker 1: last remaining nutrients. The reason you'll see more vibrant reds
Speaker 1: during some years is that stressors like an overabundance of
Speaker 1: sunlight and dry weather increase the sugar concentration in tree sap,
Speaker 1: triggering the tree to release more anthocyanins in a lastic
Speaker 1: effort to gather up enough energy to get through the winter.
Speaker 1: In addition, near freezing weather, low nutrient levels, and other
Speaker 1: plant stressors seem to trigger increased levels of antisynins. So
Speaker 1: if it's been especially rainy and overcast, you won't see
Speaker 1: much red foliage. Without bright sunlight, the trees don't need
Speaker 1: the added protection that the red pigments provide, so they
Speaker 1: don't bother producing them. If autumn just isn't the same
Speaker 1: for you without that splash of red, hopefully the weather
Speaker 1: will collaborate. Today's episode is based on the article why
Speaker 1: do Leaves change color in the Fall? On how stuff
Speaker 1: works dot Com written by Jennifer Horton. Brain Stuff is
Speaker 1: production of I Heart Radio and partnership with how stuff
Speaker 1: works dot Com, and it's produced by Tyler Klang. For
Speaker 1: more podcasts from My heart Radio, visit the heart Radio app,
Speaker 1: Apple Podcasts, or wherever you listen to your favorite shows.