Have You Wondered What Plant Roots Do. They Drink, Breathe, Feed the Plant & Anchor It. There Are Several Sorts of Root & Some Roots Aren’t Actually Roots!
Table of Contents
In this article I’m going to look at what roots are, wha they do, how they do it and why they do it. There’s a lot of botany, science and even engineering behind it, but I’m going to make it really simple.
What is a Root?
We all know what a root is, don’t we? It’s the underground part of the plant.
Well, yes and no.
There’s a bit more to it than that. Not all roots are underground and not all underground bits of the plant are roots.
For example the Banyan tree and mangroves often have roots above ground. And peanuts bury their flowers underground , that’s where they produce the peanuts, but they aren’t roots.
Here’s one definition of a root.
It’s the part of a plant that anchors the rest of the plant in the ground, absorbs water and mineral salts from the soil, and does not bear leaves or buds.
Here’s another.
In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the surface of the soil, but roots can also be aerial or aerating, that is, growing up above the ground or especially above water.
Wikipedia
So these two definitions broadly agree, but let’s look a t the details.
Plant Root Functions
A root has several different function as listed below.
Plant Anchorage
Roots anchor plants in the ground, providing stability against wind and toppling. For example Banyan tree roots spread wide for support in shallow soil. When I went to school I was taught that the trees roots spears as wide and as deep as the bits we see above ground. It was described as a dumbbell shape. But that is BS. Many trees have quite shallow roots that spread in a “root plate” just below the surface with just a few going deeper to find water when needed. But essentially the roots form a plate just below the surface. This enables the tree to use the nutrients that come from surface leaf litter decomposition, while avoiding deeper soil layers that may become waterlogged.
Plant Nutrient and Water Absorption
Plants absorb nutrients and water via microscopic root hairs. The root hairs are tiny extensions of root cells that significantly increase the plant’s surface area for efficient water and nutrient uptake. For example some of the roots of Dandelions and many grasses penetrate deep for water, whilst others remain near the surface.
Carbohydrate Storage In Plant Roots
Roots can store carbohydrates, water, and nutrients for later use. For example I used to farm sugar beet in East Anglia. Sugar beet store so much sugar for the next growing season the we have cultivated them and harvest them to make sugar in huge seasonal factories.
Internal & External Communications in Plants
Roots can communicate with each other, and with their above-ground parts, sharing electrical signals about nutrient availability and stress. Plus they can, through their mycorrhizal fungi partners communicate with other plants via the wood wide web. Plants share exchanging nutrients and water with other plants in this way.
Nutrient Sequestration
This is a spin off function in some senses as it benefits other plants more than the plant that creates it. When growing plant roots such as daikon absorb a lot of nutrients, for example nitrogen. When the plant dies the nutrients are slowly released back in to the soil and growing zone of plants. This means that soluble nitrogen isn’t leached out of the soil in winter!
The Science of Plant Roots
Different Root Types
There are two main root types: taproots such as carrots with their long, central root, and fibrous root systems such grasses that have many branching roots. I said I would keep this simple but not all the structures we might consider to be roots are roots. Potatoes are an example of this. They are root tubers which is slightly different. Beetroot are another anomaly, the swollen part is a taproot that dent go deep into the soil but largely sits above the soil.
Plant Root Zones
Roots grow in distinct zones: at the tip of the root is a shield like structure called the root cap, it’s job is to protect the tip. The meristematic zone is where growth occurs, the elongation zone allows for root lengthening, and the root hair zone, mentioned above, maximises nutrient and water absorption.
Plant Root Hairs
Root hairs are short-lived but constantly renewed, significantly increasing the surface area for water and nutrient uptake.
Interesting Plant Root Features
More On Root Hairs
Roots penetrate the soil and sequester organic soil carbon when they die
As mentioned above the job of the root hairs is to increase surface area for water and nutrient absorption. But they do far more than that and to me are the most important part of the plants roots. They are like the elite athletes of the plant world. For example root hairs are some of the fastest-growing plant cells, extending at a rate of over 1 micrometer (μm) per minute! That’s like a human hair growing several inches every hour. But despite their rapid growth, root hairs have a short lifespan, typically lasting only a few days to a few weeks. New root hairs constantly emerge behind the growing root tip, replacing older ones that have died off.
Side note! Glyphosate works by inhibiting the enzymes associated with new root hair growth. AS the root hairs die off they aren’t replaced and the plant dies. I’m not advocating the use of glyphosate, decide about that yourself!
Root Hairs: Strength in Numbers
While a single root hair is tiny, the sheer number of them makes a significant difference. A single plant can have millions of root hairs, creating a vast surface area for water and nutrient absorption. Imagine millions of tiny straws working together to slurp up resources!
How Root Hairs Taste Their Environment
Root hairs aren’t just passive absorbers. They possess the ability to detect certain nutrients and chemicals in the soil, allowing them to “choose” areas with higher concentrations of what the plant needs. Talk about a picky eater on a microscopic level!
How Root Hairs Interact with Friends and Foes
Trees grow large roots. It’s in their nature! They don’t care about the shape of planting holes
Root hairs are not just about taking in resources. They can also form symbiotic relationships with beneficial microbes like mycorrhizal fungi. These fungi help plants access nutrients that they might not be able to get on their own, while the plant provides the fungi with sugars produced through photosynthesis. On the other hand, root hairs can also detect and defend against harmful pathogens in the soil, secreting special compounds to deter them.
Mycorrhizae
Mycorrhizae form a symbiotic relationship between fungi and plant roots. The fungi help the plant access water and nutrients, while the plant provides the fungi with sugar.
Root nodules are specialised structures found on the roots of legumes (beans, peas etc) containing nitrogen-fixing bacteria. The nitrogen fixing bacteria convert atmospheric nitrogen into a usable form for the plant. Soybeans, a major source of plant-based protein, rely on nitrogen-fixing bacteria in their root nodules.
Snorkel Roots aka Pneumatophores
These root extensions grow upwards from plants in flooded environments, allowing them to breathe by taking in oxygen from the air. Examples include Mangrove trees, they have very prominent pneumatophores that help them survive in low-oxygen, waterlogged soil.
More Root Oddities
The plant kingdom is brimming with surprises. For example there are the prop roots of maize, aerial roots that sprout from the stem and provide additional support. Technically these are adventitious roots. Maize needs them because, being a grass, its root system is fibrous and it would blow over in a wind. The prop roots grow out of the stem and do what their name implies, they prop the plant up!
Another bizarre example are the strangler figs that hug their host trees with specialised aerial roots, eventually enveloping them. They use the trees as a support to reach the heights and get light.
Closer to home, and even more bizarre in some senses is mistletoe. Mistletoe possess root-like structures called haustoria that pierce into host plants and steal their nutrients!
More Root Science
Roots aren’t mindless – they respond to their environment! Positive geotropism compels roots to grow downward, ensuring a firm grip in the soil. Meanwhile, positive hydrotropism allows them to detect and chase after precious water sources. These incredible phenomena, called tropism, highlight the sophisticated communication and adaptation abilities within the plant world. And in other articles I will examine other plant abilities that are arguably essential and weird in equal measure.
