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.