Over the past 20 years, the root research laboratory and the growth chambers on the Joensuu Campus have witnessed a diverse range of studies relating to trees, other plants and soil. Researchers have studied trees that are indigenous in Finland, such as pine, birch and spruce, as well cultivated plants. An overall objective of these studies is to gain further insight into how the underground and aboveground processes of plants and trees in particular are linked to one another.
The root research laboratory and the growth chambers constitute a research environment that is available to the researchers of both the University of Eastern Finland and the Natural Resources Institute Finland, LUKE. LUKE is responsible for the activities of the root research laboratory, and the growth chambers belong to the university.
“Our root research laboratory is unique: no other laboratory in the world is exactly like ours,” says Principal Scientist Tapani Repo from LUKE.
Scientists have long been interested in the fluctuating conditions of boreal soils, as they undergo significant changes over the years.
“The environment where roots grow changes according to season, and various stress factors have an impact on root growth,” Senior Researcher Tarja Lehto from the University of Eastern Finland explains.
“Examples of such stress factors include frost heaving and freeze-thaw cycles in winter. Flooding and freezing of the flooded soil cause stress too. Moreover, the temperature and moisture of the soil during the growing season also affect root growth.”
“A speciality of our root chambers, or dasotrons, is that they allow us to grow taller trees that would be possible in regular growth chambers. We can also regulate other growth conditions that affect root growth, for example soil temperature.”
“In fact, we are currently conducting a study on soil temperatures,” Repo adds.
In the dasotrons, it is possible to perform experiments on trees that would be impossible in field conditions. They provide information on plant tolerance, which is useful when predicting the effects of extreme conditions and climate change. The studies and experiments also provide information on factors that affect growth processes, and on the interaction between the underground and aboveground parts of plants and trees.
The studies focus, for example, on the annual growth cycle of trees and the related changes occurring in the underground and aboveground processes, as well as on plant metabolism, photosynthesis and changes taking place in soil greenhouse gas emissions under different conditions. Aboveground, research can focus on water economy, such as trunk water flow and the water potential and stomatal conductance of needles and leaves, which are indicators of sufficient water intake.
“The objective of our studies is to link belowground and aboveground findings to one another,” the researchers say.
Elevated groundwater levels cause damage in just a few weeks
A significant part of tree growth takes place belowground, in the roots. The belowground processes of trees have long remained hidden in the dark, but nowadays these processes can be studied, for example, with the help of a root camera.
“20–70 per cent of the annual net photosynthetic production of a tree is projected to roots, especially the growth and function of fine mycorrhizal roots. The percentage of resources allocation between root and shoot is dependent on the age of the tree, and on environmental conditions. Fine roots are relatively short-lived, with rapid regeneration processes taking place within them. In forest soils, there can be a couple of million mycorrhizal roots per square metre, and this paints a clear picture of their extent,” Repo says.
Trees have different types of roots: the ones closest to the stem are thick and have a long life span. The fine mycorrhizal roots, on the other hand, have a short life span; yet they are responsible for the most active processes.
Recent studies have explored the flood tolerance of pine trees during the growing season, and how quickly the aboveground and underground parts of the tree react to elevated groundwater levels.
“The first small changes become visible in just a few days. After a couple of weeks, the incidence of root death increases, and photosynthesis in the aboveground parts of the tree declines. A critical time limit is from three to five weeks: trees seem to recover from shorter floods relatively well.”
“The increased incidence of root death is caused by an anoxic state. Roots need oxygen to produce energy, and anaerobic processes fail to produce enough energy during a flood,” Lehto adds.
Earlier studies have found that low soil temperatures have a greater impact on birch than pine trees. Future climate projections indicate that winters will be marked by less snow and more rainfall, and this may lead to lower than current soil temperatures.
“Birch trees may not be able to adapt to warmer climate conditions as well as we think. The effects of climate change cannot be predicted with certainty. On the other hand, we don’t fully understand the effects of current climate conditions, either.”
The researchers are currently conducting a study on plant phenology, water, nutrients and carbon sequestration.
“We study the impacts of soil temperature and changes in it on roots during the growing season,” says Research Scientist Jouni Kilpeläinen from LUKE. He is responsible for the study.
“In addition to treatments with fixed cold and warm soil temperatures, we will readjust the temperatures in the middle of the growing season from cold to warm and vice versa, and we will monitor root growth with a special camera. It takes one year to complete one experiment. This may seem like a long period of time. Luckily however, it is possible to accelerate the annual cycle of a tree by up to 2.5 fold when grown in a dasotron.”
“This acceleration doesn’t seem to have any significant adverse effects on trees, and they grow just fine like this, too,” Repo says.
Needles tolerate heavy frost, fungi even heavier
“One interesting topic of research is the frost tolerance of tree saplings and roots in particular,” Lehto says.
For experiments relating to frost tolerance, the School of Forest Sciences has a frost exposure laboratory.
In plant nurseries, the frost hardening of tree seedlings and seedling storage over the winter are important processes. When tree seedlings are stored outdoors, they are vulnerable to drops in soil temperature, which may damage the roots if there is no snow to protect them. This is why tree seedlings nowadays are commonly stored in freezer storage units. As the roots are vulnerable to frost, their storage requires great care.
“Plant nurseries need information about the optimal time to move tree seedlings to a freezer storage. Moreover, as the climate changes and snow cover decreases, it may become harder for tree seedlings to survive the winter.”
Needles and mycorrhizal mycelia, on the other hand, are surprisingly tolerant to frost.
“Needles are not the most sensitive part of a tree; in our experiments, needles survived temperatures as low as - 90 °C. Mycorrhizal fungi, on the other hand, survived even colder conditions: we exposed them to -130°C, but they just kept on growing afterwards,” Lehto says.
The growth chambers have also been used to study different potato varieties. Researchers have been especially keen to find out whether light conditions – long day versus shorter day – affect the growth and quality of potatoes, and whether it would be possible to grow potatoes of a superior quality in northern conditions,” Repo explains.
Growth facilities as part of a wider research infrastructure
Root research has been ongoing for years, but there are still many things that lack an explanation. In the future, the focus of research is likely to shift to climate change and how it will affect the growth conditions and growth of roots and, ultimately, tree growth. Furthermore, the interaction between roots and other organisms found in the soil is a topic of further research.
“Forest management practices affect not only the aboveground parts of trees, but also the growth conditions of roots. This applies to our current and future climate conditions in mineral soils, and especially in peat soils, where changes in groundwater levels have a significant impact on tree growth. Regulation of the water economy of peat soils that are used in forestry, including their drainage management, is a great challenge to forest management practices in the future, and to related research,” Repo says.
“Our understanding of other organisms found in the soil, and of their interaction, is not as complete as it should be,” Lehto says.
“The collaboration between the University of Eastern Finland and LUKE has a long and successful history. However, our research infrastructure would allow even more extensive research collaboration with, for example, companies operating in the sector. New visiting researchers would also be very welcome,” the researchers say, hintingly.