Mycorrhizal interactions do not influence plant-herbivore interactions in populations of Clarkia xantiana ssp. xantiana spanning from center to margin of the geographic range

Mycorrhizal Inoculation Enhances Nutrient Absorption and Induces Insect-Resistant Defense of Elymus nutans

The majority of terrestrial plants can form symbiotic associations on their roots with arbuscular mycorrhizal fungi (AMF) in the soil to stimulate the growth and nutrient uptake of the host plant and to improve plant resistance to insects and disease. However, the use of AMF for insect control on gramineous forages requires further study. Here, we evaluated the effects of AMF (Funneliformis mosseae) inoculation on the defense against Locusta migratoria attack in Elymus nutans. Inoculation assays showed that mycorrhizal plants had a higher resistance than non-inoculated plants, as evidenced by plants having more plant biomass, a higher nitrogen and phosphorus content, and greater lipoxygenase (LOX) activity. The results of insect damage showed that in addition to a decrease in the enzyme phenylalanine-ammonia-lyase, the activities of other plant defense-related enzymes (including polyphenol oxidase and β-1,3-glucanase) were increased. A key enzyme, LOX, belonging to the jasmonic acid (JA) signaling pathway was notably increased in mycorrhizal treatment. Volatile organic compounds (VOCs) were identified using gas chromatography mass spectrometry and the results showed that several metabolites with insect-resistant properties, including D-Limonene, p-Xylene, 1,3-Diethylbenzene were detected in mycorrhizal plants. These findings suggest that mycorrhizal inoculation has potential applications in insect management on forage grasses and demonstrates that the JA signaling pathway is essential for insect resistance in Elymus nutans.

The Influence of Arbuscular Mycorrhizal Fungi on Plant Reproduction

Arbuscular mycorrhizal (AM) fungi can influence all components of plant reproduction including pollen delivery, pollen germination, pollen tube growth, fertilization, and seed germination. AM fungi associate with plant roots, uptake nutrients, and prime plants for faster defense responses. Our literature review first identified four testable hypotheses describing how AM fungi could alter pollen delivery: (1) We hypothesize AM fungi promote floral display size. The influence of AM fungi on flower size and number is supported by literature, however there are no studies on floral color. (2) We hypothesize AM fungi promote pollen and nectar quality and quantity, and, as reported before, AM fungi promote male fitness over female fitness. (3) We hypothesize AM fungi promote both earlier and longer flowering times, but we found no consistent trend in the data for earlier or later or longer flowering times. (4) We hypothesize AM fungi alter floral secondary chemistry and VOCs, and find there is clear evidence for the alteration of floral chemistry but little data on VOCs. Second, we focus on how AM fungi could alter pollen germination, pollen tube growth, and fertilization, and present three testable hypotheses. We found evidence that AM fungi influence pollen germination and pollen tube growth, production of seeds, and seed germination. However, while most of these influences are positive they are not conclusive, because studies have been conducted in small numbers of systems and groups. Therefore, we conclude that the majority of research to date may not be measuring the influence of AM fungi on the most important components of plant reproduction: pollen germination, pollen tube growth, fertilization, and seed germination.