Human life cannot survive without plants, at least for the moment. Maybe one day we will be able to live in symbioses with algae or we will create our food in a lab, but until then, we have to bring our plants with us.
Earth plants Edit
The vast majority of plants that we eat or we use to clean the air can survive only in certain conditions. They need water, Minerals, temperature and Luminosity, of certain amounts. We might grow them in dome cities, Paraterraforming might allow us to grow them in enclosed environments, we can keep them in our spacecrafts and we will certainly need them on our terraformed worlds.
Earth has many extremophiles. They can support harsh environments, but they have never been used for human food. Also, we humans cannot survive in their conditions. We will look for places more familiar. Extremophiles might be used to bring life to places that are not good for us.
Water can be in big or small amounts. We have on Earth rice that grows in water and grains able to support dry land.
Minerals need to be in good amounts. The problem is that there are over 20 microelements needed for life. For more information, see Minerals.
Temperature must be within certain boundaries.
Luminosity must have an intensity of at least 0.1% of what is on Earth (conditions found at the orbit of Neptune). Also, plants need both red and blue light to be present at an amount of at least 0.1% of what is on Earth. For more details, see Luminosity.
If the new planet has all these conditions (by nature or by terraforming), Earth plants can be inserted.
In some cases, settlers will only have limited resources and will be forced to grow algae. They request less space, have a greater efficiency and can provide all what human body needs. Soviet scientists have made experiments on humans using Chlorella algae. Their conclusion is that humans can use them as the only food supply.
The algae alone will not be enough. We need bacteria to transform our excretions into minerals, so that they can be used by plants.
Genetically modified plants Edit
There are many bodies out there, that are not suitable for Earth plants. Settlers will have two options: grow their Earth crops in protected environment or use genetically modified plants. Since Earth plants cannot survive for long, humans will have a difficult task, to create entire ecosystems of these organisms on a planetary scale. These plants are able to extend the Habitable Zone to new boundaries.
Infrared plants Edit
Around Brown Dwarfs, light is too dim and mainly in infrared. Visible light is faint. The only solution to bring life to these bodies is to create some plants that can use infrared light. Some brown dwarfs might be so faint that it will be hard to see your path on their surface.
Red plants Edit
Some planets orbit M - type stars, which emit their light mostly in red and infrared. In the center of their habitable zone, this shouldn't be a problem, but an Outer Planet will not have enough blue light for Earth plants. So, there must be inserted plants that are able to use only red light.
Blue plants Edit
Around B - type stars, an outer planet will not have enough red light for Earth plants, but there still might be some blue. These proposed plants use only blue light and can live without red.
Ultraviolet resisting plants Edit
Some stars, like B - type stars and mainly O - type stars generate huge amounts of ultraviolet light, that might endanger Earth life. These plants need to be resistant to excess radiation in order to survive. They will use both red and blue light or, around O - type stars, mostly blue.
Ultraviolet plants Edit
An outer planet orbiting B - type stars or O - type stars will not have enough light, even in blue. Since these bodies emit a lot of ultraviolet light, this can be used by future plants to support life on their planets.
Artificial extremophiles Edit
Plants resistant to heat Edit
Some planets might have areas where temperatures increase to 70, 100 C or even beyond, but then decrease to a more comfortable value. Settlers will probably stay only when conditions allow, but will want some vegetation to exist. If the extreme heat occurs after a long cycle (once every 200 Earth days, for example), these plants could survive with help of their roots, since deep underground temperatures will not grow so high. If temperature variations are not so rare (for example, every 20 Earth days), plants will have to survive above ground. They will not have time to grow back from their roots.
Plants resistant to cold Edit
We have this on Earth. In tundra, plants are used to extreme cold. However, on an alien planet orbiting its sun every 20 Earth years, no plant will be able to hibernate a winter of 5 years. Seeds can do the job. Limited work is needed in order to make a plant to make plants have a life cycle equivalent to that planet's year.
Planets resistant to temperature fluctuations Edit
It is possible that on a planet there will be both very hot and very cold seasons. Temperatures might oscillate between -100 and +120 C. If these changes occur at long enough amounts of time, plants will have a better chance. In spring, they will start growing from their seeds, in summer all what is above ground will die, in autumn they will come back to life from the remaining roots and in winter they will survive as seeds. Genetic engineering is needed to develop plants with this life cycle.
However, if temperature fluctuations occur very fast, plants will not have enough time to grow and prepare to survive. They will have to resist as they are. It will be impossible for Earth plants to survive, but scientists can create something that would resist.
Surviving the dark Edit
One planet can rotate very slow, so that it will have over 100 Earth days of light and over 100 days of night. Thanks to a strong greenhouse effect, it will not freeze in night time. Plants, without light, have a tendency to grow high. Doing so, they run out of energy. No plant could survive too much without light. They will need to simply stop growing without light and wait for the morning.
Places for both Earth and genetically modified plants Edit
Some environments can sustain Earth plants, but geneticists might create better organisms.
Year length challenge Edit
Not all planets have the same year length as Earth. Some might have an year of only 30 Earth days, some might need over 10 Earth years. A special case is for a Tidal Locked Planet or a planet that has its axis not tilted (they don't have seasons). Earth planets can survive these environments, but new plants might be better.
Dried environments Edit
As shown on Desert planet, there might be worlds without enough water. New designed plants might be able to get their water from air in a better way then Earth lichens do, providing food for settlers.
Other uses Edit
Genetically modified plants could be used in many ways.
Carbon sequestration Edit
There could be created some algae to use carbon dioxide and release oxygen. It is known that plants produce their oxygen from water and use carbon dioxide to create organic compounds. However, following a complicated chemical reaction, these plants might be able to extract all hydrogen and oxygen from their organic molecules, creating water and oxygen. The process will result in creating atomic carbon, a black powder that will accumulate in the oceans. First it will make water black, then it will make sediments on ocean floor. If the process takes place in a lake then later dries up, there will be risks of carbon ignition.
These algae must not survive if carbon dioxide concentration drops below a certain limit. If they do, plants will not be able to survive.
Dyson trees Edit
Mining plants Edit
It has long been observed that plants can extract minerals. In very rich gold ores, there have been reported plants containing tiny gold nuggets (about 1 mm). It has been suggested to use algae to extract gold and uranium from Earth's oceans. Future scientists will look again at these ideas and maybe they will find them useful.
Symbiotic plants Edit
A more advanced human civilization will look for something never achieved. Genetically modified algae could be made suitable for surviving into human body. Then, by adding an internal source of light (probably nanobots), these plants might have enough light to produce all food needed for a human organism. At that point, humans will no longer need to eat or breath.
Artificial continents Edit
In an Oceanic Planet, we need to create some sort of land. Genetically modified plants and bacteria might be able to transform carbon dioxide or primary organic materials into a floating crust made of carbohydrates. Other plants are able to create floating islands. However, these structures are flammable.
Terraforming outer, icy planets, is possible by melting the ice, totally or partially. This way, we can create an oceanic planet. The Artificial Continents can be created with the help of genetically modified algae. It might be possible to create a Ground Insulation (a low-heat conducting layer separating the upper ocean from the lower unmelted ices) with the help of plants. Also, if the ocean has excess of salts, genetically modified algae or bacteria can solve this problem, by creating insoluble compounds that will incorporate the salts (see Salt Ocean Planet for details).
Plants have been around us since the first moments. They have grown with us, they have changed into new species and they will stay with us as long as we will exist.