Scientists have described the growing tree-stump system using cowrie trees as an example, iScience reports. Apparently, the growing trees and the stump merged into a single root system, through which water and nutrients flowed both to the trees and to the living stump. According to the researchers, in this way the cowrie could gain access to additional sources of water and nutrients. Or grafting of the roots onto each other occurred when the stump was still a growing tree.
Frequently, separately growing trees can be connected by the roots of one tree to the roots of another. Despite the fact that about 150 tree species are known that connect with each other in this way, this phenomenon has been little studied. In this way, the roots of the same tree can be connected, and, probably, self-grafting occurs in most species. The roots can be grafted onto each other trees of the same or different species. The benefits of self-vaccination are obvious - the redistribution of water and nutrients. But why grafting the roots of two different trees is needed is more difficult to explain. Even less clear is the advisability of grafting between the roots of growing trees and a stump that lives off this compound. According to the researchers, due to a more branched system of roots, trees can make better use of nearby water and nutrient reserves,or to increase mechanical stability and better resist strong winds.
Botanists have already described growing tree-stump systems, but have not studied their physiology. This was decided by Martin Bader and Sebastian Leuzinger of Auckland University of Technology, who found a leafless but live New Zealand cowrie (Agathis australis) tree stump in an area of Auckland surrounded by growing trees of the same species. Scientists have measured the flow of liquid in the stump and in two neighboring cowrie and water potentials of plants during the day and under different weather conditions, on sunny, cloudy and rainy days.
It turned out that the flows of liquid in the stump and neighboring trees constituted a single system and their distribution depended on the time of day and weather. On hot sunny days, when the water from the leaves of growing trees was actively evaporating, the liquid practically did not enter the stump, everything was taken by neighboring cowries. At night, in rainy or cloudy weather, when the evaporation of water in the neighboring trees was lower, the stump received the maximum amount of liquid.
Liquid circulation on cloudy days and at night, with low evaporation of liquid in the leaves of growing trees.
Scientists have concluded that the roots of growing cowrie and stump trees have grafted onto each other somewhere. Perhaps this happened at a time when a growing tree existed instead of a stump. Alternatively, closely growing cowrie could thus adapt to tightness, expand their root system and gain access to additional water sources of nutrients. Apparently, a larger root system was more important for growing cowries than the loss of some amount of carbon, which had to be shared with the stump (since there were no leaves on it, it could not process carbon dioxide during photosynthesis). According to the authors, such a “tree root network”, on the one hand, can help trees survive during a drought, on the other hand, it has an increased risk of spreading pathogens.
Scientists notice that they cannot draw global conclusions from a single case. In addition, they do not have direct evidence of root connection, so more research is needed. “[Our results] indicate that more research is needed in this area, especially in the face of a changing climate and the risk of frequent and longer droughts,” says Sebastian Leusinger. "They are changing our perspective on tree survival and forest ecology."
Promotional video:
In some cases, the plant can optimize its own growth strategy in order to outrun its growing competitors. As scientists have shown using the example of creeping Potentilla, in the presence of low, densely growing neighbors, plants stretched upward. If they were surrounded by tall competitors, they gave lateral shoots.
Ekaterina Rusakova