Beneath the bucolic skies of daybreak, plants must try to survive the rigors of dawn. Plants need the sun, but physiological necessities keep them chugging along after sunset and then amping up for sunrise. With the strawberry plants of Vermont’s fields and woodlands as our guides, we explore some of what plants get up to in the morning while you are shaking the cobwebs and starting your own routine.
Why do plants wait until morning to open their petals?
Since the evolution of flowers, plants have developed intimate relationships with their pollinators. Daytime bloomers, like the strawberry, attract bees and butterflies. With bees in their hives and butterflies resting on the underside of foliage overnight, there is no need to keep petals parted after sunset. Closing blooms overnight also helps to protect the strawberry’s genetic investment. The precious pollen begins to lose viability otherwise, and soggy pollen is harder for pollinators to take on a flight. Petals act as anther armor, protecting pollen from becoming weighed down with dew.
How do plants release water when stomata (leaf pores) are closed for the night?
Guttation—from the Latin gutta for drop—works the early morning shift, shuttling excess water through portals at the vein tips of leaves. These specialized holes are known as hydathodes. About the size of a human teardrop, guttation drops sit along the margins of leaves and fronds where hydathodes open to the environment. More than simply H2O, these droplets contain valuable minerals, carbohydrates, and proteins. Guttation draws in pollinators by providing a food source for them outside of nectar season. Can’t get out to Strawberry Fields in the morning? Peek at your houseplants for an example. Pothos and monsteras make beautiful drops. Once you have gotten an eye for these beads of fluid, they become easily distinguishable from the minute and indiscriminate drops of dew.
What do plants do when they can’t photosynthesize?
Overnight, when there is no light to stimulate photosynthesis, another biological pathway breaks down sugar to make energy for plant cells. This oxidative pentose phosphate (OPP) pathway also plays a critical role in keeping plants from poisoning themselves at every sunrise. Dawn creates a flick-of-the-switch metabolic imbalance that could collapse plant tissues. While photosynthesis starts up immediately when the first light hits, the cycle that uses the energized electrons from these light reactions—to make the carbon molecules plants need to build their bodies—is slower to wake. The lag time results in an excess of electrons, which bond with oxygen molecules and create unstable molecules called reactive oxygen species (ROS). These little terrors can build up and kill cells. During this tense dark-to-light transition, the OPP pathway steps in, soaking up excess electrons to break down sugar—and prevent dangerous ROS from forming.
How do plants follow the sun?
Strawberries, like many plants and naturalists, are highly responsive to the sun and its position in the sky. As dawn breaks, their leaves will fully fan out, semi-erect and facing east. You may love to start your day with yogic sun salutations, and plants have a way of performing these stretches as well. Auxins—critical plant hormones linked to many circadian-regulated functions—accumulate on the dark side of the stem of the plant. The presence of the hormone causes the cells to stretch from top to bottom. This elongation on one side of the stem pushes the flower or leaf in the opposite direction. The strawberry will continue to stretch sunward until dusk. Overnight, the plant will again engage the OPP pathway, use their petals to wrap up their reproductive bits, sweat out excess fluids and minerals, and shift to face east in preparation for the next morning.
