Document Type

Dissertation - Open Access

Award Date


Degree Name

Doctor of Philosophy (PhD)


Biology and Microbiology

First Advisor

Heike Bucking


arbuscular mycorrhizal, common mycorrhizal network, extraradical mycelium, intraradical mycelium, nitrogen, phosphate


The arbuscular mycorrhizal (AM) symbiosis is arguably the world’s most abundant and important mutualism, and brings together the roots of the majority of land plants and AM fungi to great mutual advantage. The AM symbiosis can increase the uptake of nutrients, such as phosphorus (P) and nitrogen (N), and improves the abiotic and biotic stress resistance of the host plant. AM fungi have the potential to act as biofertilizers and bioprotectors in sustainable agriculture. However, despite its significance, the mechanisms that control the resource exchange between both partners in the arbuscular mycorrhizal symbiosis are largely unknown. The main aim of this research project is to better understand the physiological mechanisms that control the cost to benefit ratios in the AM symbiosis, and to investigate how cooperation between partners is stabilized in the AM symbiosis on a cellular, whole plant and whole plant community level. This knowledge about AM interactions could help farmers to increase crop productivity under conditions that will very likely threaten food production in the future, e.g. drought by climate change, and the need to reduce fertilizer inputs. The research project addresses the following research gaps:

1. How is cooperative behavior between symbionts enforced?

2. Is the fungal partner able to distinguish cooperative partners and to allocate resources accordingly?

3. Is plant growth benefit correlated to the P and N metabolism of the AM fungus?

4. Are all AM fungi equally beneficial?

5. Is carbon a trigger that stimulates P and N transport in common mycelia networks?

We addressed these gaps in the AM symbiosis using in vitro root organ cultures and whole plant systems at the physiological and molecular level. The results indicate that plants reward better fungal partners with more carbohydrates while in return; fungal partners enforce cooperation by providing more nutrients to plants that provide more carbohydrates. This reciprocal reward system is analogous to a market economy, where trade is favored with partners offering the best rate of exchange. Our results also demonstrate that fungi are able to distinguish among host plants interconnected by common mycorrhizal networks (CMN) that differ in the benefit they provide for the CMN and that AM fungi allocate P and N to the host plants within their CMN that are able to provide more carbon. Plant growth benefit was highly correlated to the efficiency with which AM fungi were able to take up N, P and to the capability of the AM fungus to store P. Overall, our results demonstrate our hypotheses that biological market dynamics theory regulate the resource exchange and the evolutionary stability in the AM symbiosis.

Library of Congress Subject Headings

Vesicular-arbuscular mycorrhizas


Mutualism (Biology)

Plant-fungus relationships

Mycorrhizal fungi


Includes bibliographical references



Number of Pages



South Dakota State University


Copyright © Jerry A. Mensah