by Nick Carne
27 July 2019
A kauri tree stump with a story to tell.
Sebastian Leuzinger / iScience
are chipping in
to keep it
This stump of a
kauri tree (Agathis
australis) should be dead, and the fact that it isn't is
more than just a novelty.
It may mean we have
to start seeing trees not as individuals, but as part of a
New Zealand researchers
have found that the stump keeps itself alive by holding onto the
roots of neighboring trees, exchanging water and resources through
the grafted root system.
Writing in the journal iScience (Hydraulic
Coupling of a Leafless Kauri Tree Remnant to Conspecific Hosts),
they suggest the trees keep it alive in exchange for access to
larger root systems.
Sebastian Leuzinger and Martin Bader from Auckland
University of Technology stumbled upon the stump while hiking near
Auckland and were surprised to notice that it was alive but didn't
have any foliage.
When they measured water flow in the stump and in surrounding trees
belonging to the same species, they found a negative correlation,
suggesting that the roots of the stump and trees were grafted
Root grafts can form between trees once a tree recognizes that a
nearby root tissue, although genetically different, is similar
enough to allow for the exchange of resources.
"This is different
from how normal trees operate, where the water flow is driven by
the water potential of the atmosphere," Leuzinger says.
"In this case, the stump has to follow what the rest of the
trees do, because since it lacks transpiring leaves, it escapes
the atmospheric pull."
But why would healthy
kauri trees want to keep a stump alive...?
One explanation, Leuzinger says, is that the root grafts formed
before the tree became a stump. This expanded the root systems of
the surrounding trees, giving them access to more water and
nutrients, and increasing the stability of those on the forest
The others didn't notice when the stump stopped providing
carbohydrates, allowing it to continue its life with their support.
And that, Leuzinger suggests,
"changes the way we
look at the survival of trees and the ecology of forests".