The institute's scientists revealed that soil bacteria help cypress trees overcome drought conditions and in return benefit from nutrients secreted from their roots
"Here is a cypress alone, facing fire and water", wrote Ehud Menor, but a study by Weizmann Institute of Science scientists shows that the cypress is not alone at all. In drought conditions, cypresses have Surprising helpers that enable them to survive the lack of water and even thrive - Bacteria found in the forest soil. "The research findings are probably the most significant evidence so far of the symbiosis between trees and bacteria," says Dr. Tamir Klein from the department of plant and environmental sciences at the institute, who headed the research group. "And this has great ecological significance."
In many parts of the world, last summer was one of the driest seasons since the measurement began. In China, Europe, the Middle East, the Horn of Africa and parts of North America they prevailed in heavy forms, and these phenomena are only expected to increase as a result of global warming. According to Dr. Klein, climate change and the increasing prevalence of droughts in the world require us to better understand the underground mechanisms that maintain the health of trees even in harsh weather conditions, and thus possibly curb the increasing mortality of trees in Israel and around the world. "If we lose the forests, we will lose everything. The trees produce oxygen for us, absorb carbon dioxide, clean the air and regulate the temperatures," says Dr. Klein. "We must find ways to support the forests. If bacteria can support trees, and we can understand how they do it - that's a very good starting point."
Dr. Klein's journey to uncover the cooperation between trees and other organisms in the forest began a few years ago. Previous studies coming out of his research group have revealed How trees share resources with other trees and you Their interactions with fungi. The current research, led by Dr. Yaara Oppenheimer-Shanan from his laboratory, focused on the interrelationships between cypress trees and soil bacteria.
The experiment that revealed the surprising cooperation was carried out in a greenhouse at the Weizmann Institute of Science. For a month, the researchers grew cypress seedlings in forest soil in unique boxes for root research. The cypress trees that were grown were divided into two groups - a group that received a regular water supply and a group that was subjected to drought conditions. In each of the groups, half of the cypresses were exposed to two strains of soil bacteria that were isolated from the soil of the Harel forest where the cypresses also grow. The interrelationships formed between the cypress roots and the bacteria in the soil were examined with the help of several research methods, including the measurement of the trees' physiological reactions to dryness, bacterial counts, imaging using fluorescent markers of the bacterial colonies in the root areas, measurements of the compounds emitted by the seedlings through their roots and measurements of the mineral composition of the cypress leaves.
""The research findings are probably the most significant evidence so far of the symbiosis between trees and bacteria, and this has great ecological significance"
This approach, which combines microbiology, plant physiology and organic chemistry, allowed the researchers to reveal that the bacteria in the soil help the trees cope with water shortage conditions and in return benefit from secretions from the roots that nourish them. For example, it was discovered that the rate of secretions from the roots was 2.3 times greater in trees that were exposed to bacteria - both in the irrigated cypress group and in the group that was grown under drought conditions. In addition, about 100 compounds were identified in the secretions, including phenolic acids and organic acids, and the concentration of 44 of them was significantly different in the group of irrigated trees compared to the group that suffered from a lack of water. "When we added nine of the compounds as sources of carbon and nitrogen to the cultures of the bacteria, eight of them encouraged bacterial growth," notes Dr. Oppenheimer-Shannan. "Evidence that secretions are a source of food for bacteria".
Bottom line, the results of the study indicated an improvement in the health of the tree as a result of the interactions with the bacteria. Moreover, it was discovered that under drought conditions the cooperation between the trees and the bacteria balances the negative impact of the lack of water - the availability of phosphorus in the soil was maintained only in seedlings to which bacteria were added, and this availability balanced the decrease in the levels of phosphorus and iron measured in the cypress leaves grown under drought conditions.
The complete forest dictionary
Dr. Klein hopes that the research findings will advance our knowledge of forest ecology and the understanding that trees cooperate much more than previously thought. On the applied level, the findings may have important implications for improving soil health and for understanding how to support plants that are under stress as a result of a lack of resources, for example by recruiting specific bacteria to improve tree and forest health and building greater ecological resilience and stability.
"The next step is to understand exactly what the contribution of each bacteria and each group of bacteria is, and which bacteria benefit which trees," says Dr. Oppenheimer-Shannan.
"The more we learn about these interrelationships, we will be able to formulate a more comprehensive and accurate dictionary, and then we may be able to bring about desired reactions or prevent unwanted reactions," says Dr. Klein, "this is still only the beginning."
Also participating in the study were Gilad Yacovi and Mia Starr from Dr. Klein's group, Maxim Itkin and Sergey Malitsky from the Department of Life Science Research Infrastructures and two high school students, Romiel Karliner and Gal Ilon, who were selected through the Alpha program which combines outstanding high school students in the world of scientific research.
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