Scientists find hidden world under one of the oldest trees
What do you expect to find under a tree? One obvious answer is roots, or a root system. Another would be soil. But what grows in that soil separately from the tree's roots? Insects? Worms? Fungi? Bacteria? Scientists in Chile have studied a particularly long-lived tree and found some interesting answers.
The alerce (pronounced ah-LAIR-seh) is one of the oldest living plants on Earth. Known also as Patagonian cypress or its genus name Fitzroya, alerce trees are native to the Andes mountains of Chile and Argentina and to southern Chile. The largest is named Gran Abuelo or Alerce Milenia, >60 m (200 ft) tall, with a trunk diameter of 4.26 m (14.2 ft). Its tree rings have been counted to 3,622, which marks is currently accepted age, but Jonathan Barichivich thinks it may be 5,484 years old. Average sizes for alerce measure 40–60 m (130–200 ft) high, occasionally more than 70 m (230 ft), and up to 5 m (16 ft) in trunk diameter. Some alerce have been around for over 3,600 years, Compare this to the sequoia giant redwoods of California, which are 50–85 m (164–279 ft) high with trunk diameters ranging from 6 to 8 m (20–26 ft). The oldest one known is 3,200–3,266 years old.
But age alone is not what makes the alerce trees interesting. A Dover, Delaware group of scientists recently took samples of the soil under several alerce to see what they could find. They belong to the charity group SPUN (Society for the Protection of Underground Networks). Its mission is to map certain "fungal communities and advocate for their protection". The special fungi are called mycorrhizal fungi.
These fungi produce tangled interconnected networks underground where they form symbiotic relationships with plants. That means the plants are dependent on them, and they are dependent on the plants.
Most soil fungi serve an important ecological role: to decompose lignin and organic matter in soil. Lignin is the complex polymer found in cell walls of plants, about 30% of organic carbon on Earth. Only cellulose is more common. Lignin is in dead fallen trees and leaves that have died.
Why is any of that important to trees?
The decomposed material is food for trees (and other life). Fungi living under trees attach themselves to roots. Not only do they supply nutrients from soil to the trees, but the trees give them nourishment like sugars that the tree cells make. It is said that 80-90% of all plants form symbiotic fungal relationships like this.
The SPUN team took soil samples from 3 locations near each tree, and then from 4 additional locations about 5 meters away from it. These inner samples 10 cm (~4 inches) deep were pooled, as were the outer ones.
Pooled samples were then added to a special liquid solution containing ceramic or zirconia beads 0.1 mm to 0.7 mm diameter (like fine sand or the width of a human hair). These were then shaken vigorously so the beads would smash into the soil and any fungi in it. These impacts would then break open the fungal cells and release their DNA, which could be separated from the mixture and analyzed.
The researchers found 300 species of fungi under the oldest tree, not under any others that they sampled, and it was twice as many as any of the samples under other trees. That means even the younger trees still had about 150 species of fungi, but over time the older trees had developed a richer, more diverse community underground.
There are two types of mycorrhyzal fungi: the AM type which grow into the plant root cells, and the ECM type which only grow between root cells. Two different DNA databases had to be used to learn which fungi of these two types were in the samples. The MaarjAM database had DNA information for the AM mycorrhyzal fungi, and the UNITE database had DNA information for ECM mycorrhyzal fungi. The left bar graph below shows as trees age, the number of colors (different species of AM fungi) doesn't increase, but one type (brown bar species) does. On the other hand, for the right bar graph, the number of colors (number of ECM fungi species) increases as trees age. In each case, one type of fungus (represented by a pink or light green bar) is present more than others.
Basically, the diversity of the ECM mycorrhyzal fungi increases as trees age. So, larger trees somehow provide a better environment for more species of those fungi, and if they are cut down, that environment is lost and will take hundreds of years to recover.
The number and diversity of such fungi may change the entire soil ecosystem as follows:
- they suppress plant root diseases
- they also promote healthier plants by attacking plant pathogens with fungal enzymes
- they produce many vitamins which promote plant growth
- they can penetrate soil better than roots to reach trapped water and help trees in dry seasons
So, a more diverse ecosystem of fungi makes for stronger forests.
Here is a simple video (1 minute) explaining the dynamic relationship between mycorrhyzal fungi and tree root systems. https://www.youtube.com/watch?v=v88gbtKBTv4&t=68s
