Sex-Specific Responses to Mycorrhiza In A Dioecious Species Briana Deary Matt Sorcinelli

Meet the Authors Study done by Sandra Varga and Minna-Maarit Kytöviita Dr. Sandra Varga is a Faculty member of the Department of Biology at the University of Oulu in Finland Chose Finland to complete her Ph.D Thesis- “Significance of Plant Gender and Mycorrhizal Symbiosis in Plant Life History Traits” Dr. Minna-Maarit Kytöviita is a member of the Department of Biological and Environmental Science at the University of Jyväskylä Long-standing interest in evolutionary ecology of symbioses Interested in allocation of resources in symbiotic systems Research expertise include ecophysiology of symbiotic systems, arctic ecology, and soil ecology

Background Information Researchers were interested in the role of arbuscular mycorrhizae (AM) and potential sex-specific differences of host plants Believed previous studies about dioecious plants overlooked the role of AM on male and female plants Plant sexes differ in drought tolerance Drought is an important abiotic factor limiting growth and reproduction AM fungal colonization provides higher drought resistance Hypothesized that males should gain more benefit from mycorrhizal symbiosis Profit more in terms of mineral nutrition and water supply

Preliminary observations indicate males perform better in drier sites Investigated whether female and male plants of the A. dioicia species have a different relationship with AM. Preliminary observations indicate males perform better in drier sites Planned to test plants under 2 water application regimes Antennaria dioica

Key Words Antennaria dioica- perennial, clonal, herbaceous plant that grows in heaths, dry grasslands, and sandy places Common names: Mountain Everlasting, Cat's-foot, Pussy-toes Short stems of fuzzy pink flowers appear in late spring Female frequency ranging from 0-79% in Finland Asteraceae-family of A. dioica Dioecious-species in which the male and female reproductive organs occur on different individuals; sexually distinct Glomus claroideum- fungal symbiont used in experiment Ramet- Any individual belonging to a known clone

Materials & Methods Variables of the study Plant sex (male, M; female, F) Mycorrhizal inoculation (yes, AM; no, NM) Water treatment (moderate, Mod; low, Low)

Experimental Design In November 2003, seeds of A. dioica were collected from central Finland Sex was determined when plants started flowering In August 2005, researchers divided clonal fragments to grow Individual plants that were part of the study contained at least one ramet to allow representation of the same genotype Selected 14 females and 14 male individuals Before transplantation, all plants were weighed for biomass Half of the plants were inoculated with water containing spores of G. claroideum, and half received water without spores Plants were grown under greenhouse conditions for 2 months

Experimental Design Continued… Watering treatment began after 2 months Moderate= 85 mL of water Low= 57 mL of water 241 days after inoculation, plants were harvested Recorded shoot and root masses, floral shoots, inflorescences (if any), mycorrhizal colonization rate, and calculated RGR (relative growth rate)

Methods of Evaluation Chlorophyll fluorescence measurements indicate level of stress By using a fluorescence unit, researchers measured 5 fully expanded leaves of each plant Phosphorous content analysis determines content and concentration of P Mycorrhizal analysis measured the amount of AM fungal root colonization Mycorrhizal plant benefit= performance ratio between mycorrhizal and nonmycorrhizal plants >1 = the plants profited; <1 = the plants suffered Data analysis All statistical analyses were conducted with the program SPSS.

Results Plant Variables (Figure 1) Total plant biomass ranged from 0.2 to 52 grams. On average, plants with mycorrhizal symbionts with the moderate-water regime had a higher total biomass than those under the low-water regime. The opposite pattern proved true on average for nonmycorrhizal plants. Mycorrhizal presence increased shoot Phosphorus concentration. Chlorophyll fluorescence data showed a near significant affect for the moderate-water regime over the low-water which indicates higher stress in plants growing in low-water conditions.

Fig. 1. (A) Plant biomass (aboveground + root biomass in g), (B) relative growth rate (RGR in mg•g–1•day–1), (C) number of ramets, (D) ramet biomass (g), (E) shoot P concentration (% of P in dry mass), and (F) shoot P content (mg) for female (white bars) and male (gray bars) mycorrhizal and nonmycorrhizal Antennaria dioica plants in moderate- and low-watering regime. Values are expressed as means ± SE (N = 7–13).

Results Mycorrhizal Variables (Figures 2 and 3) Neither plant sex, water regime, or plant genotype affected mycorrhizal colonization. Root biomass was similar between sexes of plants that had mycorrhizal colonies. By lowering the water regime, only a marginal increase was seen for the proportion of vesicles in the roots however substantially decreasing spore production. Both sexes of plants benefited from mycorrhizal colonization in terms of biomass, RGR (relative growth rate), number of ramets and shoot Phosphorus concentration. Females benefited significantly more from mycorrhizas under the low-water regime than males both in terms of biomass and number of ramets.

Fig. 2. (A) Frequency of arbuscular mycorrhizal hyphae, (B) vesicles, (C) arbuscules, and (D) number of viable spores per pot produced by Glomus claroideum in association with female (white bars) and male (gray bars) Antennaria dioica plants, grown under a moderate- and low-watering regime, 241 d after inoculation. Values are expressed as means ± SE (N = 6–11).

Fig. 3. Mycorrhizal plant benefit, defined as the ratio between mycorrhizal and nonmycorrhizal plants, in terms of (A) total plant biomass, (B) relative growth rate, (C) number of ramets produced, (D) ramet biomass, (E) plant shoot P concentration, and (F) shoot P content in female (white bars) and male (gray bars) Antennaria dioica plants under a moderate- and low-watering regime. Values are expressed as means ± SE (N = 7–13). Values above the line denote positive mycorrhizal benefit (see Material and Methods).

Discussion When mycorrhizal fungi are absent: The data from this study reveals that the sexes of A. dioica do not vary in terms of biomass under a moderate-watered regime but under a low-water regime males typically have more biomass. This agrees with field observations of wild type plants. While males have a higher number of ramets under low-water conditions, females had overall larger ramets at both water conditions.

Results While both male and female Antennaria dioica generally benefit equally from mycorrhizal symbiosis in low-water conditions, they show a trend that female A. dioica plants benefit more than males do in well-watered conditions. Data that has been omitted from this study is from the small proportion of plants that flowered during the experiment.

Discussion When mycorrhizal fungi is present: Symbiosis between arbuscular mycorrhizas and A. dioica provides significant benefits in terms of growth and nutrients. Female plants benefit more from this relationship because they are able to acquire significant biomass in both moderate and low-water conditions. Despite the differences in biomass and growth between the plants in this study, both sexes of A. dioica seemed to provide equal amounts of nutrients to their fungal symbiont.

Discussion Since there are few studies on the effects of mycorrhizal symbiosis on plant clonal growth traits there is little data to refer to. This study, however, does agree with and build on some previous studies performed on other species (Prunella vulgaris, 1999 and Juniperus monosperma, 1992), further reinforcing the benefits of mycorrhizal symbionts. A simple, while very significant strength of this study comes from new techniques to easily distinguish the sexes of pre-reproductive plants. Sex-specific genetic markers Clonal plants

Discussion Further Studies? In general, similar studies should be undertaken on other plant and mycorrhizal fungi species in order to consider this data reproducible because so few have been performed. A specific future study that should be performed is to evaluate the differences in resource allocation and costs of reproduction between the sexes of dioecious plants. Accounting for mycorrhizal associations as mediators of mineral and carbohydrate metabolism. Antennaria dioica

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