Document Type

Dissertation - Open Access

Award Date

2018

Degree Name

Doctor of Philosophy (PhD)

Department / School

Biology and Microbiology

First Advisor

Heike Bücking

Second Advisor

Jose Gonzalez-Hernandez

Keywords

arbuscular mycorrhizal fungi, bioenergy crops, microbiome, plant microbe interactions, transcriptome

Abstract

Native perennial grasses, such as prairie cordgrass (PCG, Spartina pectinata Link), and switchgrass (SG, Panicum virgatum L.) have a great potential as bioenergy crops, because they require fewer inputs, produce more energy, and reduce greenhouse gas emissions in comparison to annual cropping systems such as corn and soybean. SG has been selected by the U.S. Department of Energy for development as bioenergy crop, but studies have shown that PCG can outcompete switchgrass in terms of biomass production. These crops can also form associations with a wide variety of plant growth promoting microbes including arbuscular mycorrhial (AM) fungi. In CHAPTER 2, we examined the beneficial microbial communities of PCG across the Upper Midwest. PCG samples were taken across Iowa, Minnesota, Nebraska, and South Dakota from a variety of environments. A high-throughput amplicon sequencing approach was used. DNA from above- and below-ground PCG tissue was extracted and amplicons targeting prokaryotic, eukaryotic, and AM fungal communities were generated. Our findings show a broad array of beneficial microbes located in PCG including well-known AM fungal species. These findings confer prior microbial surveys of PCG found in Brookings County. Alpha- and beta-diversity analysis of microbial communities indicate decreased diversity and community structure of PCG samples taken from riparian areas across the Upper Midwest. In CHAPTER 3, we investigated the impact of AM communities on the biomass production of PCG genotypes found in the Midwest. We found high genotypic variability in the biomass potential under different nutrient supply conditions and in the mycorrhizal responsiveness of different PCG genotypes. Mycorrhizal benefits were correlated to an improved phosphate but not nitrogen nutrition of the plants. In CHAPTER 4, we examined the impact of the AM fungus, Rhizophagus irregularis DAOM197198 on differential expression of mycorrhizal responsive genes in the leaves of PCG, SG, and the model grass species, Brachypodium distachyon under two nutrient input conditions. Our results show variations in the transcriptomes of each mycorrhizal grass species under low- and high-input nutrent conditions. Changes to carbohydrate metabolism, photosynthesis, sugar transporters, nutrient transporters, and response to disease signalling were most notably observed between these two nutrient conditions. In CHAPTER 5, we review the current status of inter- and intraspecific diversity of AM fungi. The 450-million-year-old AM symbiosis is formed by the majority of land plants and plays a critical role for nutrient uptake, and abiotic (drought, salinity, and heavy metals) and biotic stress resistance of the host. The fungal extraradical mycelium takes up nutrients, such as phosphate and nitrogen, and delivers them to the intraradical mycelium, where the fungus exchanges these nutrients against carbon from the host. It is known for decades that AM fungi can improve the nutrient acquisition of many important crops under low input conditions, and are able to increase plant productivity in stressful environments. However, despite their application potential as biofertilizers and bioprotectors, AM fungi have so far not been widely adopted. This is mainly due to the high variability and context-dependency of mycorrhizal growth and nutrient uptake responses that make benefits by AM fungal communities difficult to predict. In this review, we summarize our current understanding of interspecific and intraspecific fungal diversity in mycorrhizal growth benefits, and discuss the role of fungal genetic variability and host and fungal compatibility in this functional diversity. A better understanding of these processes is key to exploit the whole potential of AM fungi for agricultural applications and to increase the nutrient acquisition efficiency and productivity of economically important crop species.

Library of Congress Subject Headings

Energy crops.
Biomass energy.
Spartina.
Fungal communities.

Description

Includes bibliographical references

Format

application/pdf

Number of Pages

227

Publisher

South Dakota State University

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Rights Statement

In Copyright