Dr Tim Bleby installing sap flow sensors to
measure water uptake by deep roots of
evergreen oak trees (Quercus fusiformis) at
20m depth in Powell's cave, near Austin,
Texas. 
Image: Dr Tim Bleby

A University of Western Australia (UWA) researcher is travelling to underground caves to divine the relationship between the structure and function of deep root systems of WA trees.

Tree roots absorb water from soil, with deep roots especially important to trees because they are able to tap deep water sources, particularly during drought.

However, according to researcher Dr Tim Bleby, little is known about the contribution of roots to the total amount of water a tree needs.

“Most people think about trees and they conduct lots of measurements on the above ground portions of trees and the things that are easily accessible such as the stems and the leaves,” says Dr Bleby, from the School of Plant Biology at UWA.

“But not much is known about how that process works underground; how roots gain access to water; how deep the roots are and how they are allocated in different portions of the soil profile.

"If we find that ground level waters are dropping then a lot of these trees may become stranded, and even though they are adapted to accessing the deep water, if that deeper water were to disappear then they could be in all sorts of trouble.”

Dr Bleby also says that ground water supplies used by humans could benefit from knowledge of how much nearby trees use, possibly seeing trees felled to increase ground water availability.

“Australia is one of the driest continents on earth and we have to be careful about how we manage our water resources. We have important and globally significant forest ecosystems such as the Jarrah, Karri and Tuart forest so coupling that with the need to manage water properly, the contribution trees make to the water balance of the landscape is becoming more and more important,” he says.

His study will look at deep roots of WA karri and tuart trees that have penetrated into underground caves.  Studying roots from underground caves leaves trees relatively undisturbed, compared to traditional methods that require roots to be exhumed.

Dr Bleby’s research will include both field and laboratory work, where roots will be sampled and root structure subsequently analysed, comparing shallow and deep roots under the microscope.

“We will look at their structure and architecture under the microscope and measure a range of parameters such as how wide the vessels are, how thick the walls are, how many there are per given area and we will compare the deep roots with the shallow roots and maybe even the stems to show the differences in the structure,” says Dr Bleby.

Dr Bleby will also measure how much water passes through roots to determine their conductivity, injecting air bubbles into roots and measuring water flow rate to determine the efficiency of the roots under stress, as well as studying root action in situ.