Urban trees face many challenges as the climate changes. Long summer droughts, heavy downpours and floods all affect how trees thrive. The use of biochar in soil may be one solution to drought, while also contributing to a more sustainable urban environment.
In August, samples were collected for the third time from birch trees growing alongside a road in the Hiltulanlahti district of Kuopio. The research project of Ramya Ambikapathi, a postdoctoral researcher at the University of Eastern Finland, is nearing completion.
“I study the use of biochar in growing urban trees. The EU’s objective is to transition towards a carbon-neutral society, and this could be one application for supporting urban water management,” Ramya says.
Ramya is one of six researchers in the YUFE4 programme working at the University of Eastern Finland. YUFE4 is a programme co-funded by Horizon Europe’s Marie Skłodowska-Curie programme.
Ramya is particularly interested in sustainable urban environments. Trees are an important part of such environments, but their life in cities is different from life in forests. In addition to climate and weather, their growth is affected by factors such as air pollution, pests and construction. Healthy trees have significant effects on the well-being of city residents.
“The water availability of trees can be improved by adding biochar to the soil,” Ramya says.
Biochar has, of course, been used in plant cultivation for a long time. The biochar used in this study was produced through pyrolysis at a high temperature and in oxygen-free conditions. This gives the biochar the right kind of microporous structure.
“This kind of structure absorbs water like a sponge. The water is stored in the soil around the tree’s roots, allowing the tree to access water even during dry periods.”
The study also concerns carbon sequestration.
Biochar does not compost, which means that carbon is locked into the soil for hundreds of years.
Ramya Ambikapathi
Postdoctoral Researcher
Biochar binds more than 20 per cent more moisture in the soil
Birch trees communicate their well-being to other trees through biogenic volatile organic compounds. Gases released from tree leaves can, for example, warn other trees about insect pests or drought.
Ramya examined the soil moisture of the birch trees using a sensor and took measurements from the leaves at the top of the trees using a lift. The upper part of a tree receives more sunlight, while the lowest branches may be in the shade and other disturbance.
During the gas measurements, a birch branch was placed inside a plastic bag, and the gases were drawn from the bag into a sampling tube using pressure inlet and vacuum system. The samples are analysed in the laboratory with a gas chromatograph, which separates different gases from one another at a temperature of 250 degrees Celsius. The peaks in the curve shown on the measuring device’s display reveal which volatile organic compounds the sample contains.
“These compounds may include, for example, terpenes, which humans can also detect as the scents of trees. The sample can be used to determine, among other things, what kinds of compounds are present and how much of them are released into the air,” Ramya explains.
A compound can also be examined on the display as a chemical formula, which shows, for example, the exact number and arrangement of carbon atoms. Adding biochar to the soil changes this compound and amount.
Information on the state of photosynthesis in birch leaves can, in turn, be obtained through infrared gas analyzer. The measurement indicates, among other things, how much carbon has been bound in the leaf and how much is released into the air.
Once the results are ready, they will be used to calculate, for example, correlations between birch trees treated in different ways, and the results will be compared with birch trees grown without biochar. Samples have also been collected from these trees at different times.
The results of the study are expected in December. According to Ramya, this summer in Kuopio has been fairly neutral compared with last summer’s long dry period.
“The measurements have already shown that biochar binds more than 20 per cent more moisture in the soil.”
“In the environment, plants, soil and the atmosphere are interconnected, and carbon is a significant part of all this. The aim of the study is to gain a broad understanding of these mechanisms. Biochar is my main field of research, so I would be happy to continue working on this topic,” Ramya says.
