Over the history of the earth, plants have evolved alongside all other organisms that exist on this planet. Each species of plant fills a particular place and role within the web of the whole. This is why thinking about plants as solitary organisms isn’t really the correct way of thinking about them; healthy plants are in symbiosis with a variety of organisms that help the plant perform its daily functions effectively.
Plants form relationships with humans, animals, fungi, other plants, and microscopic organisms. In some interactions between organisms, the plant benefits and in some interactions, the plant does not.
Humans
There are many plant species that depend on humans for their survival, especially ornamental and agricultural species. We have selectively bred them over centuries and even millennia for traits we prefer, like extra juicy fruit, or edible grains, rather than the traits that they would require to live away from our watchful gaze.
Rice is a type of grass, and here it is being farmed by human beings. Image source
Humans also like to kill certain plants that we consider weeds, and introduce non-native plants into a new environment which can have a negative impact long-term. Read my article about weeds if you’d like to know more about them.
Some plants become incorporated within our culture and take on a special significance within our collective psyche. It’s hard to imagine the Australian identity without the famous eucalyptus gum trees with their signature sickle-shaped leaves and fuzzy flowers.
Animals
One of the major ways that plants interact with animals is as food, for the better or worse in terms of the plant’s health.
Sometimes plants want animals to eat their flesh, as in the examples of many fruits that have their seeds spread by animals, and flowers that attract pollinators with pollen and nectar.
Sometimes, however, the relationship can seem a little bit more one-sided.
Large herbivores may eat smaller leaves, pull up roots, or eat small plants whole. Sometimes, if enough of the rootstock remains undisturbed, the plant is able to recover, however some of the time this will kill the plant.
These animals do, however, feed the plant in the future, or at least its offspring, with manure after it has finished digesting the plant material.
Munching and sucking insects may feed on a few leaves and leave the plant’s overall health in tact, or they may kill the plant by taking a majority of the photosynthesising material, or create openings for pathogens to enter.
Nematodes are animals that are similar to worms and insects but closely related to neither (or any other animals we usually think of). They consist of plant pest varieties which colonise root systems and kill plants, and beneficial varieties that control a range of pests including ants, weevils and fleas.
You can read more about plant pests and diseases through the articles in my Plant Health Problems category.
Allowing some pest insects in your garden ensures that predator insects have a constant food source and are able to stick around for longer. This may mean some damaged leaves or small losses of crop yield, but this is the cost of avoiding pesticides.
Plants actually release chemicals and hormones that let predator insects know that there is a meal waiting for them at the source of the scent.
This rose has had an aphid pest infestation, and then predatory wasps have come and laid eggs inside the aphids. You can see the aphid “mummies” here, with an embryonic wasp living inside the unfortunate aphids’ bodies. We’ll never know whether these predatory wasps were called by chemicals released by the plant. Photo via Plants Grow Here.
If you have the right predator pests in the area, they should be able to find the pests and control them before the outbreaks become too serious.
Pollinators often require flowers to live, just as plants require pollinators to spread their genetic material onto the next generation. Flowers also encourage other beneficial insects, such as the lacewing that eats pests in its larval stage, but requires pollen to feed on in its adult life cycle.
Animals also fertilise the soil with their droppings and decaying bodies, so all of the nutrients taken from the plants should be making their way back into the soil, ready to be taken up again by the plants. Beneficial animals, insects and other organisms are required to break down the carcasses and manure during this process.
Fungi
Fungal species play a wide range of roles in the garden and nature, from breaking down dead plant material into compost, to killing weak plants so new healthy ones can come up, to colonising the roots of plants.
Mycorrhizal fungi colonise the roots of a plant (myco= fungal, rhizal=roots), and help break down nutrients and deliver them to the plant, in return for carbon that the plant readily gives up in exchange.
Saffron milk caps are the edible mushroom from a mycorrhizal fungi connected to conifers that Europeans brought to Australia along with their trees. See this guy poking up through the grass and pine needles. Photo via Plants Grow Here.
These mycorrhizal fungi penetrate the root of the plant, and continue their network throughout the rhizosphere (the part of the soil containing roots) within the soil and roots of other plants. They literally communicate with the plant to see what sort of nutrients it has in abundance, what it’s lacking, whether pests are attacking it as well as a range of other topics.
Probably also “how’s the weather?”
Because this fungal network is interconnected between all of the roots in the area and beyond, this means that all of the plants are connected to each other through a kind of fungal web that is analogical to our our very own human world wide web network.
According to New Scientist, mycorrhizal fungi “trade resources with plants like a stock market”.
These fungi are willing to trade nutrients that plants are desperate enough to pay a premium to buy, or have enough abundance to sell on the cheap, for carbon which plants make as a result of photosynthesis. In this way, one plant can help another to get all of the nutrients they need, with fungi playing a mediating role.
Plus, there are many fungi varieties out there that are highly nutritious for humans, and are incredibly delicious raw and when cooked. While foraging for food is a lot of fun and a great way to connect to our food, make sure you go with somebody who has a lot of experience picking and is able to distinguish the edibles from the inedible and even poisonous varieties.
Especially when it comes to fungi, because there are a lot of very poisonous species that are known to give a long, horrible, untreatable death.
Bacteria and Other Microscopic Organisms
There are a wide variety of other organisms that don’t fit into the animal or fungal categories, including bacteria and viruses. Just like all of the other categories, the roles of these organisms can vary in terms of the help it offers the plant.
Microscopic organisms (including microscopic fungal organisms) are integral to breaking down organic materials into compost that plants can use, as well as protecting plants against pathogens.
Some microscopic organisms take out weak plants, or those that have grown in the wrong place, to make room for the best plant for the space. We consider these pathogens a problem, but they are integral to the overall ecosystem.
Other Plants
Plants communicate with other plants both above and below the ground.
This article mentioned above that plants release chemicals and hormones to alert predator insects to the existence of pests, but they also alert other plants nearby who may be able to make themselves distasteful or increase poisons to keep the pests away.
One plant can also warn others of pests and diseases through the fungal network, so the same message is being broadcast through separate mediums. As mentioned above, plants also trade nutrients through the fungal web.
Conclusion
In the natural world, there are checks and balances that keep everything consistent. Only the strong and the necessary survive, and often species have made themselves indispensible through mutualisation in an effort to stave off extinction.
Plants willingly allow themselves to be colonised by some organisms, and actively fight off other organisms using all of the tools at their disposal, including chemicals they’ve made, or by “calling in” some beneficial organisms that will help them defend themselves.
A truly healthy plant is a popular plant; one whose friends depend on it for survival and have its back when enemies are at the gate.