When the going gets tough, we all need a helping hand, and trees are no different. Researchers at the Department of Plant Sciences at the Weizmann Institute of Science have discovered that in drought conditions, cypresses get help from beneficial bacteria in the soil in a kind of cooperation that enables them to survive and thrive. “Our study probably provides the best evidence to date that trees and bacteria can coexist,” said Dr. Tamir Klein, head of the research group. “It has great ecological significance.”
In many places around the world, the summer of 2022 will be one of the driest on record. Parts of China, Europe, the Middle East, the Horn of Africa and North America are suffering from severe drought, and such extreme weather conditions are expected to increase due to climate change. According to Klein, the increasing prevalence of droughts creates an urgent need to understand the underground mechanisms that keep trees alive in extreme weather, in order to reduce the increase in tree mortality in Israel and beyond.
“If we lose forests, we lose everything because trees produce our oxygen, absorb carbon dioxide, clean the air and regulate the temperature,” he explained. “That’s why we need to support our forests. And if bacteria can support trees and we understand how they do it, that’s a great starting point.”
Klein’s journey to reveal the cooperation between trees and other organisms in the forest began years ago. In his previous studies, he investigated how trees share resources with other trees to stay healthy, and how they maintain symbiotic relationships with fungi.
The latest study, led by Dr. Yaara Oppenheimer-Shaanan, who is a microbiologist in Klein’s lab, focused on the interaction between cypress trees and the beneficial bacteria present in the forest soil. For one month the researchers grew cypress saplings in custom-made boxes filled with forest soil, which were placed in a greenhouse at the Weizmann Institute of Science.
The cypresses were divided into two groups: one was regularly watered, and the other was deprived of water. In each group, half of the cypresses were exposed to soil bacteria collected from the Harel Forest, where these cypresses grow.
The research team investigated the interaction between tree roots and bacteria using several methods, including measuring the trees’ physiological reactions to drought, performing bacterial counts, imaging bacterial colonies in the root zones using fluorescent markers, analysis of compounds released by seedlings through their roots and evaluation of the mineral composition of cypress leaves.
Through this multidisciplinary approach, which combines microbiology, plant physiology and organic chemistry, researchers have identified the amazing cooperation that takes place underground between trees and soil bacteria: Bacteria help trees cope with lack of water and in turn, benefit from the secretions from the tree. medicine.
For example, the number of secretions from the roots is more than double in trees exposed to bacteria, compared to trees without, in both the irrigated cypress group and the group growing in drought conditions. In addition, the scientists identified about 100 compounds in the secretions, including phenolic and organic acids, and the concentration of almost half of these compounds was significantly different between irrigated trees and those suffering from a lack of water. .
“When we added nine of the compounds to the bacteria, as sources of carbon and nitrogen, eight of them stimulated the growth of the bacteria,” Oppenheimer-Shaanan said. “This is evidence that secretions are a food source for bacteria.”
Overall, the results of the study suggest that the health of the trees improved as a result of the interaction with the bacteria. In addition, during droughts, the cooperation between trees and bacteria can compensate for the negative effects of lack of water. Soil phosphorus availability was maintained only for cypresses exposed to bacteria, and this availability accounted for the reduction in phosphorus and iron levels measured in the leaves of cypresses grown under drought conditions.
A complete dictionary of the forest
Klein hopes that these research findings will improve our knowledge of forest ecology and the understanding that trees engage in greater cooperation than previously believed. At the applied level, the findings may have important implications for improving soil health and learning how to support plants that are stressed due to lack of resources. For example, recruiting specific bacteria can help improve tree and forest health and build greater ecological stability and resilience.
“The next step is to determine the exact contribution of each bacterium or each group of bacteria, and which bacteria benefit which trees,” Oppenheimer-Shaanan said.
“This is just the beginning,” Klein said. “The more we know about these interactions, the more we will be able to create a comprehensive and accurate dictionary, and this should allow us to reach the desired results, or prevent those that are not want, to take care of our forests.”
The work is published in the journal eLife.
Yaara Oppenheimer-Shaanan et al, A dynamic rhizosphere interplay between tree roots and soil bacteria under drought stress, eLife (2022). DOI: 10.7554/eLife.79679
Provided by the Weizmann Institute of Science
Citation: Underground symbiosis counters drought (2023, July 13) retrieved 13 July 2023 from https://phys.org/news/2023-07-underground-symbiosis-counters-drought.html
This document is subject to copyright. Except for any fair dealing for the purpose of private study or research, no part may be reproduced without written permission. Content is provided for informational purposes only.