Scientists from the University of Tartu used innovative methods to figure out the gene sequences of plants beneath the surface of the soil. This led to the discovery that species richness among them is much greater than one can see above the ground.
The species-rich meadows of the temperate latitudes can sometimes contain dozens of plant species growing in an area that is no bigger than the palm of a hand. But as a rule, perennial plants have roots, rhizomes and bulbs hidden in the soil. On these species-rich grasslands, these could constitute up to three-fourths of plant biomass. Until now, it wasn’t possible to sort roots into species according to their visible characteristics.
There are many more plants belowground than aboveground. Inga Hiiesalu is taking samples of plants and the roots beneath them. Photo from personal archive.
In the study, samples of soil were taken from experimental plots at a meadow in Põlvamaa, near the river Ahja. The number of plants visible above-ground was counted, and then plants from the soil samples were sequenced, based on DNA taken from their roots. To achieve this, a specific region of chloroplast DNA was used to differentiate between plant species.
It turned out that at the same spot, up to two times more plant species can live in the soil belowground than aboveground.
“It is really a new approach in plant ecology. Our article is one of the first to reflect this,” said Inga Hiiesalu, the chief author of the article and a doctoral student of UT macroecology workgroup.
How to explain the existence of so many more plants under the ground? According to Hiiesalu, the situation could be compared to a TV set standing in the corner, waiting for someone to turn it on. Just like the TV set, plants wait for suitable environmental conditions when they can grow above-ground shoots as well. Plants could spend years in this type of waiting mode.
Another explanation is that the roots or rhizomes of a plant could be located a few feet away from the shoots and this way the roots can cover a much larger area.
In addition to the discovery that there are many more plant species below the ground, the study revealed that the well-known patterns of species richness from aboveground don’t hold water belowground . It is widely known that the diversity of aboveground plants declines when the fertility of the soil increases. The meadow at Põlvamaa, mentioned above, was no exception. Conversely, the underground richness surprisingly increases with higher fertility.
“Studying the underground diversity of plants gives us a consistent picture of the structure and functioning of plant communities. Had we observed only the parts above the surface, we’d have seen just the tip of the iceberg,” said Professor Meelis Pärtel, the supervisor for Inga Hiiesalu’s doctoral thesis.
Last year, with the help of his colleagues, Pärtel presented an entirely new theory about dark diversity.
Hiiesalu I, Opik M, Metsis M, Lilje L, Davison J, Vasar M, Moora M, Zobel M, Wilson SD, & Pärtel M (2011). Plant species richness belowground: higher richness and new patterns revealed by next-generation sequencing. Molecular ecology PMID: 22168247
