Fynbos has the thinnest roots of any plant in the world, scientists have discovered.
And it’s not just a fact that might come in handy at a pub quiz. It is a fundamental trait that ensures the survival and diversity of the world’s richest floral kingdom.
Fynbos roots — which are between two and four times thinner than any others known to science — are so efficient at harvesting nitrogen from soil that they leave none behind for bigger plants.
“The thin roots of fynbos are the below-ground weapon creating miserable conditions for nutrient-demanding forest plants,” said University of Cape Town botanist and emeritus professor William Bond.
This explains the sharp boundaries between hot, open fynbos and cool, shady Afrotemperate forest areas that are a feature of the Cape floral kingdom.
Bond is one of the authors of a new paper on the Proceedings of the National Academy of Sciences which reports on four years of research carried out in locations such as the pristine Jonkershoek Nature Reserve in Stellenbosch and Orange Kloof on Table Mountain.
He worked with several other UCT scientists and lead author Mingzhen Lu from the Santa Fe Institute and Princeton University in the US to work out how fynbos plants maintain the poor soil they thrive in — and how adjoining forest areas end up being so different.
On the way to achieving these objectives, they discovered that an erica root has to be 1,752 metres long to weigh a gram. This is about the same as the length of 15 football pitches laid end to end.
For the last 400-million years, since plants colonised land, roots have been the engine driving the water cycle, the nutrient cycle, the carbon cycle, worldwide.
— Mingzhen Lu of Princeton University
To achieve the same result, an indigenous pock ironwood tree growing a few metres away needs roots only 40 metres long.
The difference is due to the differing soils created by the two biomes, and to prove this the scientists tried to grow seedlings of three indigenous trees — wild peach, bladdernut and Cape saffron — in the fynbos soil of Jonkershoek.
Half the seedlings were planted in post-burn open soil to allow the roots to compete with fynbos, and the other half inside PVC collars that removed or reduced below-ground competition for nutrients.
The seedlings fertilised with nitrogen grew five times faster.
“We now see that it is not the intrinsic soil properties, but plant feedbacks to the soil that create misery for forest saplings.”
He said fynbos fires help by destroying nutrients in the soil and allowed fynbos to “favour its own persistence by modifying its environment. On the other side of the biome divide, the forest is doing the converse thing.”
Lu said his findings, while studying for his doctorate, suggested what he called “alternative stable states” in proximity with the same underlying geology and climate patterns can be maintained through root traits — an insight that could be critical to conserving threatened ecosystems.
“Roots are the foundation of biodiversity,” said Lu. “For the last 400-million years, since plants colonised land, roots have been the engine driving the water cycle, the nutrient cycle, the carbon cycle, worldwide.
“It is profound to see microscale plant traits, such as root thickness, linked to macroscale emergent ecosystem patterns.”
Lu described the sharpness of the boundaries between fynbos and forest biomes: “In the summer, you are scorched by the sun in the fynbos, then you take one step into the forest, and you’re engulfed by cool humidity and you see moss on the trees. It’s like a binary switch, zero to one. Boom, you’re in another world.”
Lu’s doctoral supervisor, Lars Hedin from Princeton University in the US, said the ecological competition unfolding in the quartz sand underlying fynbos and forest was fascinating.
“What’s novel here is that the roots — the world’s thinnest roots — actually play a central role in this game,” he said.
“Because if you have them and I try to invade, with my thicker roots, you will capture every nitrogen atom before I can; and there’s not many of them in this soil to start with.
“And it’s not just one species doing this, but the whole community has evolved with this strategy, making the soil just too miserable for anything else to survive.
“As humans, we think that bigger is always better. Be as productive as possible. That has driven biological theory for more than a century.
“Our research suggests that there’s a completely different strategy here, and it depends on manipulating your environment. Keep the soil miserable, burn any nutrients that try to accumulate. I mean, these plants don’t have brains, but over evolutionary time, it’s a strategy that works.”
Would you like to comment on this article?
Sign up (it's quick and free) or sign in now.
Please read our Comment Policy before commenting.