LIFE TRSCA: Water that changes the world: from plant to landscape

The changing water level directs the development of leaves in certain plants, influences the distribution of plants and plant communities, and shifts the mowed vegetation, thus changing conditions over a larger area.

The water level on the intermittent Lake Cerknica fluctuates, which has recently, as a consequence of climate changes become more unpredictable. Therefore, only plants adapted to such conditions can thrive well in these habitats. They are named amphibious plants and can thrive underwater and also when the water level retreats. One of the adaptations that allows them to succeed in such diverse environments is heterophilly. This means the different forms of the leaves are developed on the same plant: submerged, floating or aerial. 

On Lake Cerknica, water is the driving force that determines the growth of plants and other organisms. With every change in the water regime, the conditions on the Lake Cerknica also change, enabling or preventing the development and living of animals and plants. As part of the project LIFE Trsca, we study how the lake's management affects plants, including amphibian species. Any interference with the lake and its tributaries can have severe consequences for the plants in this area.

Extreme heterophylly in Sium latifolium (greater water-parsnip), where we can see the leaves typical for submerged plants and those found in typical terrestrial species on the same plant. Such marked heterophylly makes it difficult to believe that such very different leaves belong to the same plant. 

Looking at the different leaves of arrowhead (Sagittaria sagittifolia), you would never guess that it is the same plant. Submerged leaves are very thin and ribbon-like, similar to the leaves of typical aquatic plants. Terrestrial leaves are spear-shaped, with a waxy coating called the cuticle, which protects the leaves from excessive water loss. 

Not only plants but the water is constantly changing the entire landscape of the Cerknica Polje. Meandering rivers like Stržen erode their banks on one side, deposit the sediments on the other and reshape the bottom of the Lake Cerknica. At high discharges, the transportation capacity of the river can move large amounts of organic matter and loamy sediments. 

After the period of heavy rain in the middle of September, the water level rose suddenly and flooded numerous surfaces that were mown shortly before the water rose. The water floated the mown reed, sedges and other plants and moved vast piles of this material with the help of the wind that later got stuck at vital reed stands. Some of the meadows were buried under dead plant material, causing anger among these owners. 

Article was prepared by the Biotechnical Faculty of the University of Ljubljana.