I don’t know about you, but twice a year, Day Light Savings always messes me up. For at least a week after we fall back or spring forward, I’m a wreck—I can’t focus, I’m more tired than usual.
Part of the problem is because that 1 measly hour change messes with the human body’s circadian rhythm. You may have heard of that term before, in Latin circadian roughly translates to “about day”, meaning this rhythm is about ~24hrs long.
Although we still don’t understand all of the details of circadian rhythms, here are some things we do know:
Circadian rhythm in plants:
The most visible way that plants demonstrate their circadian rhythm is by tracking the sun with their leaves or flowers. In fact, the first time this motion appeared in scientific reports was in the 1700s, so we’ve know about it for a while. Even today, we don’t understand exactly how plants control their circadian rhythm.
Sunflowers are excellent for observing this solar tracking. What’s absolutely wild about these flowers is that they reset themselves at night. They follow the sun from east to west during the day, but overnight they reset back to face east for the next sunrise. This demonstrates that, although they may follow the environmental cue of sunlight, that’s not the only driver. Without sunlight at night, they still somehow move back to face east (not south or north) and they are reset back to east before the sun rises again. Check out this video to watch sunflowers in action: https://www.nature.com/news/video-sunflowers-move-to-internal-rhythm-1.15548
Circadian rhythm in orchids:
The most obvious example of circadian rhythm in orchids that I’ve observed in my own plants is flower scent. Have you ever bought a plant that the grower swore smelled beautiful, but every time you smell it, there’s no scent? Try smelling that flower at different times of the day—including the middle of the night. The chemicals responsible for the scent are expensive for the orchid to make. Most orchids won’t waste the energy or resources to make those chemicals if their pollinator isn’t active. It’s like calling your night-owl friend at 6am. Why bother when you know she’ll be asleep and won’t answer? You have a better chance of her answering if you wait for a time when you know she’ll be awake.
For instance, I have an oncidium that only has a scent in early afternoon while my mom has a brassolaeliocattleya (Blc.) that has the most beautiful, powerful scent…at 2am. The difference is that my oncidium’s target pollinator is probably most active in the middle of the day, while the Blc.’s pollinator is likely nocturnal.
Biomes – an area of land with specific environmental conditions that is home to animals and plants adapted to those conditions
The greatest diversity of orchids are found in tropical and subtropical regions of the world. These are areas with a lot of rain and warm average annual temperatures. Epiphytic orchids are almost exclusively found in these biomes because their roots grow out into the air where they have no soil or media to moderate temperature or protect them from water loss. Meanwhile, cooler climates are home to terrestrial orchids that can survive harsh winters with their roots and rhizomes safely buried under ground.
Rainfall and temperature are the most common environmental factors used to define biomes.
These environmental factors are largely controlled by where on the planet the biome is located. Tropical biomes are found right along the equator, while subtropical biomes are a bit further away from the equator.
For a more information, check out the charts below!
Because most scientific articles and texts are published using metric units, I spruced up this graph to include imperial units (inches and Fahrenheit) so my fellow Americans could follow along. (Figure adapted from Whittaker, R.H. Communities and Ecosystems. New York: Macimmilian, 1975; and Rickefs, R.E. The Economy of Nature. New York: W. H. Freeman, 2000.)
This graph, called the Whittaker Biome Model, breaks down common biome types over a range of temperatures and rainfall levels. For instance, from this graph we can estimate that a tropical rainforest receives 80-160 inches of rain per year with an average temperature of ~70-85°F.
This graph also tells us a little bit about the organisms (plants, animals, insects, etc.) that live in those areas. For instance, an epiphytic orchid might grow well in a tropical rainforest or a tropical seasonal forest because the temperatures stay warm all year round and both receive sufficient rainfall. However, a grassland or desert would be too dry for an epiphytic orchid while the taiga and temperate deciduous/coniferous forests would be too cold.
Sometimes there are overlaps between biomes that would make this graph very confusing, so not every biome is represented here. For example, this graph doesn’t identify subtropical rainforests, but we can still talk about them in terms of their rainfall and temperature. Subtropical rainforests are characterized by receiving a lot of precipitation, at least 30 inches. They also tend to be cooler than tropical rainforests, although the temperature rarely goes below freezing. Orchids living in subtropical rainforests will be more tolerant of cooler, drier conditions.
This map of the planet is colored for biomes, rather than countries. If you look carefully you’ll notice that there are lateral bands/zones of particular biomes. From equator to poles, it goes: Tropical rainforest – tropical grassland – desert – temperate forest – taiga – tundra. This makes sense because we know that average annual temperature decreases as we move away from the equator.
Jen Schmidt is a graduate student at Cornell University who, with the help of her mother (Barb) is turning into a crazy plant lady at a young age.