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Mark van Kleunen: plant species and what they can tell us

Prof. Dr. Mark van Kleunen, a Dutch biologist at the University of Konstanz, is investigating the impact of climate change on specific alpine plant species, including clonal plant species that produce an identical copy of their genetic code due to vegetative reproduction. Mark van Kleunen is specifically focused on genetic variations of the dwarf willow (Salix herbacea) found in alpine environments.

Prof. Dr. Mark van Kleunen, biologist at Konstanz University © private

Climate change impacts human beings and nature and it is assumed that it will remain one of the major drivers of plant diversity. Faced with changing environmental conditions, plants have three solutions: they can either migrate, adapt or become extinct. Climate change can therefore potentially lead to the appearance of plants that are not endemic to a particular environment. “Plants that we grow in our gardens but that are not endemic to our geographic area might spread,” said Prof. Dr. Mark van Kleunen who is investigating the impact of climate change and human activity on a number of plant species. He is also investigating ways to stop negative effects (e. g. decreased growth and seed production) on the plant species under investigation. 

Clonal growth, i.e. the ability of plants to reproduce asexually, is regarded as one of the most remarkable strategies that plants possess in order to adapt to cold environments. Some species, including dandelions, reproduce asexually, which means that the offspring are exact genetic copies of the parent plants. Around 70% of all plants in Central Europe are clonal species. Such species have outstanding capabilities. “The parent plants can remain physically connected and exchange resources with their daughter plants for a long time; this is referred to as clonal integration,” said van Kleunen. Clonal species can determine the direction where they place their roots and therefore where their daughter plants grow. This is a type of behaviour known as ‘foraging response’ and enables plants to establish their roots and offspring in an environment that they consider to be advantageous.

Professor van Kleunen is currently investigating this phenomenon in clonal plant species in closer detail. He also hopes to find out whether it gives them an advantage over plants that do not have the same ability. Van Kleunen is using many different plant species for his investigations, including Salix herbacea, which he is exploring with his doctoral student Janosch Sedlacek and scientists from Switzerland and Sweden in a small cooperative project (Sinergia project) funded by the Swiss National Science Foundation.

Salix herbacea – the smallest tree in the world

Salix herbacea (dwarf willow) is the smallest tree in the world and grows in arctic areas of Europe, North America and the Alps. Salix herbacea grows at around 1900 m above sea level. It usually consists of a stem of around 5 cm in length and three to five leaves. The majority of the tree grows underground, forming a dense network of rhizomes, i.e. underground flattened mats of tillers.

“Due to the fact that the plants reproduce asexually, individual Salix herbacea plants can be extremely old. Computer models suggest that this species may well disappear from many alpine areas some time in the future as a consequence of the changing climate,” said van Kleunen highlighting that the models cannot provide information on the alpine area as a whole as the Alps are characterised by a broad range of different microtopographies and climatic conditions that cannot be covered by a single model. In addition, Salix herbacea might also have a certain adaptive buffer, which could enable it to adapt to altered climatic conditions to a certain extent by way of phenotypic plasticity and evolution. A high phenotypic plasticity value means that environmental influences have a strong impact on individual phenotypes. Van Kleunen is investigating the genetic structures of Salix herbacea with the aim of determining the potential of clonal species.

Field studies with dwarf willows

The researchers are carrying out Salix herbacea field studies in the Swiss Alps close to the city of Davos. The team also involves van Kleunen’s colleagues from the WSL Institute for Snow and Avalanche Research (SLF). The project partners carry out their investigations at altitudes of between 1900 and 2500 metres above sea level. “These are typical alpine areas that are covered with snow until summer. And this is where we find many Salix herbacea plants,” said van Kleunen. The transect studies are being carried out on three different mountains: Wannengrat, Jakobshorn and Schwarzhorn. The lower and upper parts of the transects include two large areas where the researchers have marked 100 Salix herbacea specimens. One area is located in a typical snow bed and the other on a ridge where the snow melts away in early summer.

Salix herbacea project field work on Jakobshorn mountain. © Mark van Kleunen

The researchers are pursuing two approaches. They measure the plants in the field, determine their size, look at their morphology, etc. These data are then combined with DNA data to determine the plants’ genetic similarity. “We use the Ritland method to determine the heritability of quantitative traits,” said van Kleunen. The Ritland method is a regression approach in which the phenotypic similarities are correlated with the relatedness of the two individuals. “Kermit Ritland’s method states that if there is a correlation between phenotypic similarity and relatedness, then the variability of the phenotypic traits has a heritable component,” Mark van Kleunen explains. In addition, the researchers transplant clonal Salix herbacea fragments reciprocally between different microhabitats in order to determine their phenotypic plasticity. “This enables us to estimate the heritability of phenotypic variation and its evolutionary potential,” said the biologist.

Heritability analysis using the Ritland method

The researchers are investigating three typical plant properties with the aim of assessing changes in the Salix herbacea habitat that result from the changing climate. First, the researchers assess the production time of leaves and blossoms, which provides information about the onset and end of a plant’s flowering time. Second, they focus on the storage of carbohydrates in the plant stems and leaves to glean information on the location and its deficiencies or diversity. “We are trying to find an answer to the question as to whether a plant displays ‘sink limited’ or ‘source limited’ growth,” said van Kleunen. ‘Source limited’ plants do not grow effectively as they do not have access to high enough carbon sources. ‘Sink limited’ plants have access to high carbon sources, but are unable to use it, as the low ambient temperatures reduces meristem activity with the result that growth processes are limited and carbohydrates stored. “Studies have shown that the alpine tree limit is determined by ‘sink limitation’ and we are trying to find out whether this is also the case for Salix herbacea,” said van Kleunen whose team is also investigating the performance characteristics of plants with regard to the production of fruit and new stems.

The researchers use molecular genetics methods such as microsatellite analysis to compare inheritable genetic variations of plant traits. Microsatellites are short, non-coding DNA sequence repeats. “Microsatellites are neutral DNA markers that can be used to assess the relatedness of plants in nature,” said van Kleunen. Combined with the phenotypic similarities of plant properties, the microsatellites provide information about heritable genetic variations. “These molecular data have already shown that the relatedness of the investigated plants differs,” said Prof. Dr. van Kleunen. 

The results will now be analysed and further investigations will be carried out. “Surveys that attempt to assess the impact of climate change on flora need to run over a long period of time because the evolutionary adaptation of some species takes a long time,” said Prof. van Kleunen summarising his research.

About:

Prof. Dr. Mark van Kleunen did his doctoral thesis on the evolution of clonal species life histories under the supervision of Markus Fischer and Bernhard Schmidt. His research interests brought him to the University of KwaZulu-Natal in South Africa where he was involved in a project investigating the pollination of invasive plant species. He returned to the research group led by Markus Fischer at the University of Berne (Switzerland) and was able to establish his own research group. This position was good preparation for his current position as professor at the University of Konstanz, a post he took up in February 2011.

Website address: https://www.biooekonomie-bw.de/en/articles/news/mark-van-kleunen-plant-species-and-what-they-can-tell-us