Antagonism in the Mycorrhizal Symbiosis – in search for mechanisms

Table of contents

Plant growth responses to arbuscular mycorrhizal fungi (AMF) are highly variable, ranging from mutualism in a wide range of plants, to antagonism in some non-mycorrhizal plant species and plants characteristic of disturbed environments. This project focuses on a number of potential mechanisms that can explain why AMF suppress growth of some plant species. Background: Arbuscular mycorrhizal fungi (AMF) play a key role in ecosystems by influencing plant growth and ecosystem functioning. Most studies have focused on the positive effects of AMF on plant growth and nutrition. However, plant growth responses to arbuscular mycorrhizal fungi (AMF) are highly variable, ranging from mutualism in a wide range of plants, to antagonism in some non-mycorrhizal plant species and plants characteristic of disturbed environments. The precise mechanisms responsible for the negative effects of AMF on some plants received almost no attention as most research focused on the positive effects of AMF on plant growth. This project focuses on a number of potential mechanisms that can explain why AMF suppress growth of some plant species. Aims: The following key hypothesis are investigated in this project:

  1. The cost-benefit relationship with AMF varies among plant species. Plants that respond negatively to AM fungi invest carbon into AMF, without benefit (nutrients) in return.
  2. Plants that respond negatively to AM fungi invest carbon in mycorrhizal networks while coexisting plant species receive the benefit of such networks.
  3. AM fungi suppress growth of some plants by exuding allelopathic compounds.
  4. Plants that respond negatively to AM fungi cannot block colonization by AM fungi under conditions in which AM fungi are unfavorable

Relevance: Recent studies have provided important insights into the role of AM fungi in ecosystems. These soil fungi can stimulate plant diversity and productivity and enhance stress resistance in a wide range of plants. Until now, research largely focused on the positive effects of AM fungi on plant growth, ignoring that an estimated 17'000 - 39'000 species are non-mycorrhizal, including a large number of weeds. A few recent studies suggest that many non-mycorrhizal plants may be suppressed by AM fungi. Moreover, the fact that some mycorrhizal plants also respond negatively to AM fungi points to surprising interactions in the rhizosphere. AM fungi may exude allelopathic compounds with suppressive effects on plants, including a number of weeds. This fact may in the future lead to the isolation and development of bio-herbicides. Biological weed control is a key issue because herbicide use accounts for 45% of all pesticides used in agriculture, and this percentage is yearly increasing. Hence, the development of novel ways for weed control, such as proposed here, is crucial for the development of sustainable farming systems. The findings of this project will be highly relevant for sustainable agricultural production. Moreover, the study will lead to a better understanding of plant-microbe interactions, mycorrhizal and soil ecology, and crop-weed interactions, and will stimulate our understanding of the role that microbes play in the soil.

Participants

Verena Säle (PhD student)

Dr. Fritz Oehl (supervisor)
Prof. Dr. Marcel van der Heijden (responsible professor and co-supervisor)
Dr. Franco Widmer (cooperating partner)
Dr. Hannes Gamper (cooperating partner)