• Hayley E. Park

Roots, Rhizomes, Rhizobia, and the Subterranean Ecosystem

Hey there! What a week it has been, with an even bigger one coming up…

I’m in the process of trying to pin down a research topic for my thesis, and have narrowed it down to looking at some portion of plant-soil microbiome interactions. To nobody’s surprise there is a massive amount of STUFF going on under the surface of the soil, and so to say that I’ve “narrowed” it down is not much narrowing at all.

Corn grows through an essential mycorrhizae relationship between plants and soil fungus.

But more important than research stuff, my sister is getting married this week to a wonderful guy and I’m just so happy for them. This week involves a whole lot of coordination of people, food, and flowers (to name a small portion). Though their wedding doesn’t have too much to do with the Seed Underground, I love them both and have to tell everyone that this is a special week.

That said, this week we’re ACTUALLY going underground here at the Seed Underground to take a look at a bunch of stuff that plants are doing that we barely (if ever) see. So without further ado, let’s get into it:

Remember last week I glorified the grape hyacinth and mentioned bulb plants? Let’s start there with a quick explanation of what a bulb even is.

  • Bulbs are modified, short stems that function in storing food for a plant during the dormancy stage.

  • Bulbs are characterized by having multiple leaf-y layers (think onion layers) and are one of many plants – bulbing or otherwise – that require long periods of cold to change them from the vegetative part of their life cycle to the reproductive part.

The most famous of all the "bulb" plants.

So, bulbs require a long period of cold, like winter to start flowering. Similar to humans who inadvertently bulk up a little during the winter holidays to stay warm, bulbs have a big, round energy storage region that feeds them through the winter. You can even watch this happen by pulling up a bulb at the end of winter to see that the round bulb has mostly disappeared over the course of winter, only to be replenished by the spring and early summer photosynthesis.

It’s a bit odd to think of stems existing underground, since basic botany splits plant parts at the soil surface. There are actually several other underground stems beyond just bulbs, and I’ll tell you about one more of my favorites: Rhizomes.

What’s a rhizome? Have you ever seen one before? The answer is definitely YES. Two very popular rhizomes are ginger and turmeric, and that’s reason enough to get me excited about this type of stem.

To sum up a rhizome: it’s an underground stem that runs horizontal to the ground, and has both shoots (for aboveground growth) and roots that branch off of the rhizome. That’s it. They’re pretty cool in that they help plants like ginger spread out in an area without having to go through a full reproductive cycle.

Now, as I speed talk my way through uncomfortable situations in this world I often mix up rhizomes with another word: rhizobia. They practically sound the same, but the difference is immense. But mostly it’s because both things are related to roots and rhiza is Latin for “roots.”

Rhizobia is a name that describes a whole bunch of naturally occurring bacteria that live in the soil that can form symbiotic (mutually beneficial) relationships with legumes (bean-y things). This term isn’t actually a taxonomic classification, but it’s widely used to refer to this type of bacteria. Since there are hordes of bacteria in the soil that don’t necessarily do anything with legumes, let alone helpful things, it’s a good descriptor.

Latin Etymology:

Rhiza + Bios

Root + Life

Rhizobia are awesome, and not just because their etymology makes them sound like a ultra-chic kombucha made from organic carrot and beet extract (and let’s be real, I’d drink it). Rhizobia are symbiotic with plants. They’re great little helpers. In exchange for some housing inside the root, they take the nitrogen in soils and convert it to a plant available form.

In case you’re wondering what’s so important about nitrogen, it’s in EVERY SINGLE AMINO ACID, and therefore every protein that the plant makes. It’s also an element in the base pairs that make up DNA. So this little nutrient is super importante.

Check out those white root balls, those are the nodule-homes of the rhizobia.

There are so many organisms that live in the soil that I imagine it would be tough to describe them in an entire blog, let alone a single post.

There are bacterial species that break down chemicals and could be used to clean up polluted soils, coincidentally these same species are a very commonly a source of infection in hospitals. Then you have mycorrhizal relationships between plant roots and underground fungi. These relationships sometimes can be parasitic, but in other cases they are beneficial. Orchids, for example, require their seedlings to use a mycorrhizal relationship to get food during their early life stage.

The soil microbiome is CRAZY. I feel like it needs a sports commentator giving the play-by-play of what’s going on, who is helping who, and calling out any dirt-y moves. Anyways, thanks for sticking around for another week of my quasi-scientific exploration of the botanical world.

Let me know what you think of this look below the soil surface. I love to hear your thoughts and questions.