In a study that may help areas affected by a changing climate, an international team of researchers led by Scott Mackay of the University at Buffalo College of Arts and Sciences have used computer models to determine how conifers are able to survive drought conditions. Using simulated pines and junipers, it seems that the key lies in how the tree roots access water.
If you could see a tree as it really is, the bit above ground would seem like a minor part of the whole plant. Like an iceberg, many trees are mostly underground with extensive root systems stretching out in all directions in search of water and nutrients. It's an impressive sight that few have a chance to see in its entirety and it's also one that is a headache for botanists because studying the root system is often very difficult and risks killing the tree.
This is unfortunate because the roots are at the, well, root of how some kinds of trees, like conifers, can survive severe droughts and scientists haven't been sure how this works. Does the tree rely on roots that have already tapped into a water supply or does it grow new ones when rain becomes scarce?
To answer this question, Mackay's team turned to computer models that simulated how pines and junipers react to a five-year drought based on conditions similar to those found at the Los Alamos Survival-Mortality (SUMO) experiment site in New Mexico. What they found was that when the trees already had their roots in water, they survived, but the ones that tried to grow roots to the water all died.
According to Mackay, the reason for this is that growing roots requires the tree to supply water and carbon from the canopy to the root system. This takes energy and resources away from the tree as a whole and the roots can't grow as far and as fast as needed, so the tree dies.
Aside from potentially explaining an old arboreal question, this insight may help to preserve coniferous forests under climate change pressure.
"Scientists are trying to forecast what's going to happen to the world's biomes under climate change, and models need to be physiologically realistic," says Mackay. "During past droughts, there's lots of evidence of what we might think of as hydrologic refugia – pockets of woody species that have survived droughts by tapping into deeper water resources. Some models tend to overestimate tree mortality because they're not able to capture some of these refugia. If we can learn more about these refugia and how they're established, we can use that knowledge to create better models."
The study was published in New Phytologist.
Source: University at Buffalo
