Sex‐specific responses to mycorrhiza in a dioecious species

Abstract

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.

Dioecious species and arbuscular mycorrhizal symbioses: The case ofAntennaria dioica

“…In addition, previous studies under greenhouse confirm that the interaction with AM fungi and A. dioica is sex-specific: 15,16 females and males of A. dioica differed in their response to the same AM fungal species (Glomus claroideum). Females gain greater AM benefit than males when grown without stress conditions, while under stress conditions (drought or low pH) the mycorrhizal benefit is lower and similar in both sexes.…”

“…Females gain greater AM benefit than males when grown without stress conditions, while under stress conditions (drought or low pH) the mycorrhizal benefit is lower and similar in both sexes. 15,16 These studies suggest that the sexes may provide different amount of photosynthates to the fungus and that they also differ in the benefit derived from the symbiont. However, in natural ecosystems 15 and ii 16 were conducted under greenhouse conditions, while the studies iii 13 and iV 14 were conducted in the field.…”

“…15,16 These studies suggest that the sexes may provide different amount of photosynthates to the fungus and that they also differ in the benefit derived from the symbiont. However, in natural ecosystems 15 and ii 16 were conducted under greenhouse conditions, while the studies iii 13 and iV 14 were conducted in the field. the sexes (F, females and M, males) are plotted separately except in the study ii where only F are shown because only one M produced flowers.…”

“…In addition, little is known about how AM symbiosis can be influenced by other biotic interactions 3 and abiotic factors. 15,16 Finally, the possibility that AM fungi play an important role in the evolution of sexual systems as have been proposed for herbivores and pollinators, 17,18 deserves more attention.…”

Sex ratio and spatial distribution of male and female Antennaria dioica (Asteraceae) plants

“…In AM symbiosis, nutrients and water are delivered to the plant from the soil whereas the fungi receive carbon in exchange (Smith and Read 1997). It has recently been shown that the sexes of dioecious (Varga and Kytöviita 2008;Varga and Kytöviita 2010a) and gynodioecious plants (Varga and Kytöviita 2010b) may gain sex-specific benefits from their AM symbionts and different patterns of root colonisation have been reported between the sexes of dioecious plants (Eppley et al 2009). This sexual dimorphism between plants and AM fungi has been related to the different resource needs and allocation patterns between the genders (reviewed in Varga 2010).…”