Summary1. Arbuscular mycorrhizal (AM) symbiosis has been shown to enhance some plant traits to which pollinators are known to respond. Moreover, in gynodioecious species pollinators prefer hermaphrodite flowers over female ones, but the role of fungal symbiosis in sex-specific pollinator attraction is unknown. 2. We examined how plant gender dimorphism and AM symbiosis affect floral visitors and reproductive output in the gynodioecious plant Geranium sylvaticum. Floral visitors were monitored in a common garden experiment using mycorrhizal plants inoculated with either Glomus claroideum or Glomus hoi and in non-mycorrhizal condition. 3. We hypothesized that because of the larger flower display and pollen presence in hermaphrodites, (i) hermaphrodites receive more floral visitors than females. However, as females produce higher numbers of seeds than hermaphrodites, we predicted that (ii) effective pollinators visit both sexes equally and that (iii) AM symbiosis, although affecting floral characteristics and insect behaviour in general, should not have sex-specific effects on insects that transport pollen. 4. Our results confirm the hypotheses as hermaphrodites received 1AE5 times as many floral visitors than females. However, the most important pollinator group, the bumblebees, did not prefer either sex, which may be important for the maintenance of both sexes in gynodioecious populations. We further corroborated that AM symbiosis, although affecting flower size and the amount of pollen, did not affect bumblebee behaviour, whereas other hymenopterans showed a deterrence for G. hoi inoculated plants. 5. This work reports the impact of AM symbiosis on the behaviour of floral visitors in a sexually dimorphic plant species. Positive interactions between plants, floral visitors and AM have been documented previously. However, potential negative tritrophic interactions between plants, floral visitors and AM may also occur. Our results suggest that plant sex and the mycorrhizal status of the plant also influence floral visitor groups that are unlikely to carry out pollination. This may benefit the plants if these floral visitors carry fungal diseases and consume pollen and nectar without effectively vectoring pollen.

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Most plant species grow in association with arbuscular mycorrhizal fungi in their roots forming arbuscular mycorrhizal (AM) symbiosis. The positive effects of this type of symbiosis on plant's performance are well known and established. However, relatively little is known about how AM symbiosis affects plant reproduction, even though reproduction is probably the most important component of life history. This review begins with a summary of the existing data on plants with monomorphic breeding systems, as most of the research has been performed using hermaphroditic and monoecious plants. Later, the limited number of studies examining mycorrhizal effects on plants with dimorphic breeding systems is detailed. Finally, several key areas for future investigations are highlighted. These include examination of the incidence of sex-specific interactions in other plant species with dimorphic systems, the influence of AM symbiosis in seed germination and establishment in plants with different gender, or the study of the mechanisms behind the AM effects seen on plant reproduction. Evidence suggests that AM symbioses are beneficial for plants with monomorphic and dimorphic breeding systems, as AM symbioses improve both sexual and asexual reproduction. However, the effects observed strongly depend on both the plant and the AM fungus species involved. Plant interactions with AM fungi and the outcome of these interactions may further depend on the gender of the host: sex-specific patterns of root colonization and sex-specific benefits from AM symbioses have been reported in several plant species. However, the incidence and the importance of sex-specific relationships between AM fungi and plants are still largely unexplored.Additional key words: clonal growth, plant sexual dimorphism, plant-fungus interactions, sex-specific interactions, sexual reproduction. Resumen Revisión. Efecto de las micorrizas arbusculares en las características reproductivas de las plantas con dimorfismo sexualLa mayoría de plantas crecen en asociación con hongos micorrícicos arbusculares en sus raíces formando micorrizas arbusculares (MA). Los efectos positivos de este tipo de simbiosis para el desarrollo de plantas son bien reconocidos. Poco se sabe de los efectos de las MA sobre la reproducción; aunque sea probablemente el rasgo más importante de la estrategia vital de una planta. Esta revisión detalla los datos disponibles sobre los efectos de las MA en la reproducción de plantas con sistemas de reproducción monomórficos y dimórficos. Se presentan los datos existentes sobre los efectos en la reproducción en plantas con sistemas de reproducción monomórficos, dado que la mayoría de los estudios se han efectuado sobre plantas hermafroditas y monoicas; se detallan los estudios que examinan los efectos de las MA en plantas con sistemas de reproducción dimórf icos; y se proporcionan líneas de investigación futuras. Los datos sugieren que las MA son mayoritariamente beneficiosas tanto para plantas con sistemas monomórficos cómo dimórficos, ya que m...

In most studies about dioecious plants, the role of arbuscular mycorrhizae (AM) and the potential sex-specific differences between the plant hosts have been overlooked. Because plant sexes frequently differ in drought tolerance and AM fungal colonization provides higher resistance to drought, we investigated whether the relation of mycorrhizal fungi with either male or female Antennaria dioica plants differs using a factorial experiment. We hypothesized that because AM usually increase growth rate and male plants usually grow larger than females, males should gain more benefit from the mycorrhizal symbiosis in terms of mineral nutrition and water supply. Because of higher demands of carbohydrates (C) in males, we expected males to allocate less C resources to the mycorrhizal fungus so that the associated fungi should benefit less of the association with males. In contrast to our initial hypothesis, the male plants, although faster growing under drought, did not gain more symbiosis-mediated benefits than did the females, and both sexes seemed to provide resources equally to their fungal symbiont. Therefore, we conclude that the two plant sexual morphs provide equal amounts of C to their fungal root symbionts and that they can gain specific benefits from the symbiosis, which, however, depend on soil water availability.

Both plant sex and arbuscular mycorrhizal (AM) symbiosis influence resource acquisition and allocation in plants, but the interaction between these two components is not well established. As the different plant sexes differ in their resource needs and allocation patterns, it is logical to presume that they might differ in their relationship with AM as well. We investigate whether the association with AM symbiosis is different according to the host plant sex in the gynodioecious Geranium sylvaticum, of which, besides female and hermaphrodite plants, intermediate plants are also recognized. Specifically, we examine the effects of two different AM fungi in plant mass allocation and phosphorus acquisition using a factorial greenhouse/common garden experiment. Cloned G. sylvaticum material was grown in symbiosis with AM fungi or in non-mycorrhizal condition. We evaluated both the symbiotic plant benefit in terms of plant mass and plant P content and the fungal benefit in terms of AM colonization intensity in the plant roots and spore production. Our results suggest that G. sylvaticum plants benefit from the symbiosis with both AM fungal species tested but that the benefits gained from the symbiosis depend on the sex of the plant and on the trait investigated. Hermaphrodites suffered most from the lack of AM symbiosis as the proportion of flowering plants was dramatically reduced by the absence of AM fungi. However, females and intermediates benefited from the symbiosis relatively more than hermaphrodites in terms of higher P acquisition. The two AM fungal species differed in the amount of resources accumulated, and the fungal benefit was also dependent on the sex of the host plant. This study provides the first evidence of sex-specific benefits from mycorrhizal symbiosis in a gynodioecious plant species.