Plants continuously have to decide how to invest their resources. If they invest more into growth, they might become more susceptible against diseases or easier attacked by herbivores. On the other hand, a strong investment into their defence system will be at the expense of growth. Vicki Huizu Guo Decker from Umeå University has found that certain defence chemicals, influence the decision making process in Aspen trees. Vicki Huizu Guo Decker has successfully defended her thesis on Friday the 4th of November.
The production of defense chemicals is costly for a plant. Vicki Huizu Guo Decker has worked with Aspen trees that have evolved different strategies to invest their resources. Those trees produce different levels of tannins and salicinoids which are phenolic defence compounds. Vicki Huizu Guo Decker wanted to know how these genetically different Aspen trees (also called Aspen genotypes) react to additional nitrogen nutrition and how this affects the plant associated microorganisms.
The soil nitrogen content influences the plant's decision to grow or to defend. Nitrogen nutrition normally promotes plant growth and inhibits the synthesis of tannins in the tree leaves. Vicki Huizu Guo Decker found that there is a connection between the genetically inherited level of tannins and the trees’ strategy to deal with limited nitrogen availability. Aspen trees with low tannin levels grew better on poor soils with low nitrogen levels than trees that contain a lot of tannins. “Trees with high levels of tannins invest more energy to keep these levels high”, says Huizu Vicki Guo Decker. “That is why they grow less when nitrogen is limited. This strategy can be of advantage for the tree when it is for example attacked by insects.”
Another factor that is thought to influence the fitness of the tree are endophytic fungi. These are plant associated microorganisms that co-exist with the tree but do not cause any disease symptoms. Instead, their presence might improve the fitness of the tree against plant attacking insects. Vicki Huizu Guo Decker found that the composition of the fungal community on Aspen leaves is strongly related to the level of phenolic compounds. Especially salicinoids influence the structure of the fungal community.
The relationship between endophytic fungi and the host plants get 
Treatment with the Aspen leaf beetles and resulting deeding damages. even more complex when additional environmental factors are added like plant attacking insects. Huizu Vicki Guo Decker worked with Aspen leaf beetles. This specialised beetles and their larvae feed on Aspen trees and the larvae even use the phenolic compounds from the tree for their own defence. Guo Decker showed that the fungal composition becomes less specific to the respective respective genetic Aspen genotype when the Aspen leaf beetles are attacking the tree.
Treatment with the Aspen leaf beetles and resulting deeding damages. even more complex when additional environmental factors are added like plant attacking insects. Huizu Vicki Guo Decker worked with Aspen leaf beetles. This specialised beetles and their larvae feed on Aspen trees and the larvae even use the phenolic compounds from the tree for their own defence. Guo Decker showed that the fungal composition becomes less specific to the respective respective genetic Aspen genotype when the Aspen leaf beetles are attacking the tree.“Studying how plants response and adapt to their environment is very complex because there are so many factors influencing the decision of a plant about where to invest its resources”, concludes Vicki Huizu Guo Decker. “Plants always try to optimize themselves towards a dynamic balance between defence and growth. This is very sophisticated and delicate because it is not only of concern for them as individuals but also for their interaction with their associates like endophytic fungi.”
Phenolic compounds like tannins and salicinoids are not only for plant defence systems important. Also the human immune system is profiting from them. Tannins are found in many species throughout the plant kingdom. They are very well known for their antioxidant effects. Salicinoids on the other hand are very specific to the Salicaceae or Willow plant family that includes beside aspen also poplar, willows and cottonwoods. Already since the 19th century, salicinoids are used as anti-inflammatory agents.
Text: Huizu Vicki Guo Decker, Anne Honsel
Pictures: Vicki Huizu Guo Decker
Pictures: Vicki Huizu Guo Decker
For more information, please contact:
Huizu Vicki Guo Decker, Department of Plant Physiology, Umeå University
Phone: +46 90 786 5489
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Phone: +46 90 786 5489
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Information about the public defence of the dissertation:
On Friday 4 November, Huizu Vicki Guo Decker, Department of Plant Physiology, Umeå Plant Science Centre, Umeå University, has defended her dissertation entitled:
Phenolics, Nitrogen, and Biotic Interactions: A Study of Phenylpropanoid Metabolites and Gene Expression in the Leaves of Populus tremula.
Faculty opponent was George Newcombe from the Department of Forest, Rangeland, and Fire Sciences, University of Idaho, USA
Phenolics, Nitrogen, and Biotic Interactions: A Study of Phenylpropanoid Metabolites and Gene Expression in the Leaves of Populus tremula.
Faculty opponent was George Newcombe from the Department of Forest, Rangeland, and Fire Sciences, University of Idaho, USA