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Oulun yliopiston väitöskirjat

SIGNIFICANCE OF PLANT GENDER AND MYCORRHIZAL SYMBIOSISIN PLANT LIFE HISTORY TRAITS, ACTA UNIVERSITATIS OULUENSIS A Scientiae Rerum Naturalium 549

ISBN-13:	978-951-42-6138-1
Kieli:	englanti
Kustantaja:	Oulun yliopisto
Oppiaine:	Luonnontieteet
Painosvuosi:	2010
Sidosasu:	pehmeäkantinen
Sijainti:	Print Tietotalo
Sivumäärä:	154
Tekijät:	VARGA SANDRA

20.50 €

Most plants grow in association with arbuscular mycorrhizal (AM) fungi in their roots forming theso-called AM symbiosis. AM symbiosis is usually beneficial to the host as it improves plantsurvival and performance. However, AM symbiosis also entails a cost to the plant in terms of thecarbon allocated to the fungus. In sexually dimorphic plants, more than one type of individual canbe recognised with regard to their sexual expression or gender. The cost of reproduction in theseplants will differ in relation to the relative investment in male versus female function, as the femaleand the male sexual functions incur different costs. This different cost of reproduction may betranslated into differences in other plant functions between the sexes as all functions are connectedthrough trade-offs. Therefore, since sexes differ in resource needs and allocation patterns, and AMmediate resource acquisition and allocation patterns through imposing both costs and benefits tothe plant, the sexes of dimorphic plant species may possess, at least theoretically, a differentrelationship with their AM roots symbionts. In this thesis, I have investigated whether the sexes in sexually dimorphic plant species differin their mycorrhizal relationship, and if so, in which ways. Several plant life history traits werestudied in the dioecious species Antennaria dioica and also in the gynodioecious Geraniumsylvaticum using greenhouse, common-garden and field experiments. Resource acquisition,resource allocation, and both plant and fungal benefits from AM symbiosis were considered. Mainly beneficial effects of AM symbiosis were observed in both sexes of the two dimorphicplant species for most of the studied plant life history traits. Overall, both partners benefited fromthe AM association. However, several sex-specific benefits were detected which were notuniformly present in all experiments for any given trait. Moreover, the responses observed incertain life history traits were dependent on both the AM fungal and plant species involved in thesymbiosis. Remarkably, plants gained sex-specific benefits from the same species of AM fungiand the fungal benefit differed depending on the sex of the host plant. In addition, mycorrhizalbenefits were lost under certain environmental conditions. To summarise, the results obtained in this study highlight the complexity of AM interactions.My results suggest that the plant-mycorrhizal fungus relationship may differ depending on the sexof the host plant. Through sex-specific effects on survival, growth and reproduction of the hosts,AM fungi may play a role in the evolution of the life histories in the studied species. In addition,sex-specific relationships between plants and their mycorrhizal symbionts may have potentialimportant consequences for the population dynamics of the sexual morphs and the coevolution ofthe mycorrhizal relationship.

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