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Introduction. A well-supported pattern among dioicous bryophytes is male rarity. However, few assessments of bryophyte sex ratios have been made across environmental gradients to assess the role of...

Silvery-Thread Moss (Bryum argenteumHedw.) is an undesirable invader of golf course putting greens across North America, establishing colonies and proliferating despite practices to suppress it. The goal was to grow genotypes ofgreen(growing in putting greens) andnative(growing in habitats outside of putting greens)B. argenteumin a common garden experiment, allowing an experimental test of life-history traits between genotypes from these two habitats. Seventeen collections ofgreenand 17 collections ofnative B. argenteumwere cloned to single genotypes and raised through a minimum of two asexual generations in the lab. A culture of each genotype was initiated using a single detached shoot apex and was allowed to grow for 6 mo under conditions of inorganic nutrients present and absent. Compared with genotypes from native habitats, genotypes ofB. argenteumfrom putting greens exhibited earlier shoot regeneration and shoot induction, faster protonemal extension, longer (higher) shoots, lower production of gemmae and bulbils, and greater aerial rhizoid cover, and showed similar tendencies of chlorophyll fluorescence properties and chlorophyll content. Cultures receiving no inorganic nutrients produced less chlorophyll content, greatly reduced growth, and bleaching of shoots. Mosses from putting greens establish more quickly, grow faster, produce more abundant rhizoids, and yet do not produce as many specialized asexual propagules compared with mosses of the same species from native habitats. The highly managed putting green environment has either selected for a suite of traits that allow the moss to effectively compete with grasses, or genotypic diversity is very high in this species, allowing a set of specialized genotypes to colonize the putting green from native habitats. Successful golf course weeds have been able to adapt to this highly competitive environment by selection acting on traits or genotypes to produce plants more successful in competing with golf course grasses.

Dehardening (deacclimation) to water stress is an integral phase of desiccation tolerance (DT) in bryophytes. Shoots of the desert moss Syntrichia caninervis were harvested and dehardened after exposure to field CO2 concentrations of 380 ppm (ambient) and 550 ppm (elevated). The dehardening period consists of three phases, with shoots from the first phase (3–7 d) the least able to recover from a rapid-drying event and the second (12–18 d) and third (21–27 d) phases characterized by shoots hardening to desiccation and approaching control levels. Response variables following this pattern include tissue chlorosis, protonemal emergence and area, shoot growth resumption, total regenerative shoot production, and probability of fungal attack. Dehydrin levels did not increase over time during the 27-d experimental hydrating period and thus could not account for the observed constitutive hardening to DT. This first experimental sequence on extended dehardening in bryophytes counters the assumption that field shoot...

Three prominent life history patterns attributed to dioecious species of mosses (low sex expression, male rarity, and low frequencies of sexual reproduction) were investigated in the desert moss Syntrichia caninervis along an elevation gradient in the Spring Mountains of the Mojave Desert (U.S.A.). Low elevation patches exhibited significantly lower frequencies of sex expression, individuals with fewer inflorescences, and fewer male individuals. Sexual reproduction was infrequent at all elevations, with only seven of 85 patches showing evidence of recent sporophyte production and only nine of 708 perichaetia being fertilized. After factoring out abortive sporophytes, the percentage of patches maturing sporophytes was 5.9% and the estimated fraction of fertilized perichaetia was 0.7%. In addition, as elevation increased from low to middle/high elevation, individuals of Syntrichia caninervis exhibited significant increases in biomass, total stem length, number of ramets, and ramet length. The decre...

Phenotypic variation occurs in many populations of plants. When this variation occurs along an environmental gradient, the immediate question is whether the variation is attributed to phenotypic plasticity, ecotypes, or some combination of the two. The moss Syntrichia caninervis appears morphologically variable along an environmental gradient changing rapidly from low light, low temperature, and high moisture levels in the understory microhabitat to high light, high temperature, and low moisture levels in the intershrub microhabitat. We tested for the presence of physiological variation using recovery from a heat-shock event in a mimicked microhabitat light environment, and for morphological variation using a common garden with the ultimate goal of attributing observed variation to plasticity, genetic variation, or a combination. The results suggest that plasticity plays a large role in trait variation. Photosynthetic recovery depended on the current light levels of an environment and not the orig...

Bryophyte population sex ratios are predominately female-biased, at least with respect to plants expressing sexual structures. One hypothesis to explain this bias is that males produce sexual structures less often than females, but occur at similar frequencies, a hypothesis termed the "shy male hypothesis." Another nonexclusive possibility is that offspring sex ratios (as sporelings) are biased and populations retain this bias. To test these hypotheses, we examined sex ratios in expressing and nonexpressing shoots for the cosmopolitan moss Bryum argenteum collected in the field, and in shoots grown from spores in the lab. An examination of 154 collections of B. argenteum from native habitats and urban settings in the USA revealed that populations were significantly female-biased (>80% female). Male rarity was most pronounced in aridland regions of the Mojave Desert and California chaparral; males were significantly more common in altered urban habitats and in high elevation native habitats. When all shoots from clumps representing three mixed-sex, sporophytic populations were grown to sex expression, male nonexpressing shoots were not found to be significantly more abundant than expected based on the field expressing shoot sex ratio, lending little support to the "shy male hypothesis." Offspring sex ratios derived from sporelings were not significantly different from 1:1, thus not explaining the sharply female-biased population ratios observed in the field. We propose that factors between spore germination and adult maturation, including clonal dynamics, are causing the female-biased population and within-clump sex ratio imbalance of B. argenteum.

Patches of the dominant biological soil crust moss (Syntrichia caninervis) in the Mojave Desert were subjected to transplant experiments to test the survivability of crustal transplantation due to source or destination microhabitat. After a period of 27 months, all the reciprocally transplanted and replanted sections had survived. However, percent cover of the reciprocally transplanted patches declined 20–50% relative to initial cover compared to a decline in cover of 36–52% for the replanted patches. Similarly, shoot density declined an average of 26% in the transplants and replants. Shoot mortality was essentially negligible through the first 21 months of the study and then declining across all treatments to approximately 5–10 dead shoots/cm2. However, this shoot death was also observed in equivalent densities in the host patches, indicative of a community-wide decline in plant health that was probably related to a regional rainfall deficit over this period. A tendency existed for plants moved from a shaded site to have reduced shoot density in the new site, and plants moved into exposed sites lost significantly more cover than plants moved into shaded sites. These seemingly conflicting trends result from one of the transplant treatments, the shaded to exposed, exhibiting a greater loss in shoot density and decline in cover than its reciprocal transplant, exposed to shaded. For soil restoration of disturbed bryophyte crusts, we recommend using as source material both the exposed and the shaded portions of the crust but avoiding moving Syntrichia from a shaded site into an exposed site.

The cost of sexual reproduction is incurred when the current reproductive episode contributes to a a decline in future plant performance. To test the hypotheses that a trade-off exists between current sexual reproduction and subsequent clonal regeneration and that resources limit reproduction and regeneration, plants of the widespread moss Pterygoneurum ovatum were subjected to induced sporophytic abortion, upper leaf removal, and nutrient amendment treatments. Sexually reproducing plants were slower or less likely to produce regenerative structures (protonemata or shoots) and produced fewer regenerative tissue areas or structures. The ability and the timeline to reproduce sexually and regenerate clonally were unaffected by an inorganic nutrient amendment. However, when leaves subtending the sporophyte were removed, the sporophytes were less likely to mature, tended to take a longer time to mature, and were smaller compared to sporophytes from shoots with a full complement of upper leaves. Our fi ndings indicate that plants investing in sexual reproduction suffer a cost of decreased clonal regeneration and indicate that sporophyte maturation is resource-limited, with upper leaves contributing to the nutrition of the sporophyte. This study represents only the second explicit experimental demonstration of a trade-off between sexual and asexual reproduction in bryophytes.

1. Two competing hypotheses relating to thermostress were proposed to understand skewed sex ratios in Syntrichia caninervis, a reproductive investment hypothesis and a wildfire selection hypothesis. 2. Nearly all shoots from both sexes remained viable (regenerated in culture) following exposure to 120 °C for 30 min, thus setting a new upper thermotolerance record for adult eukaryotic organisms for a minimum 30 min exposure time. 3. Males regenerated faster than females, produced more biomass, and suffered less fungal attack than females. Findings support the wildfire selection hypothesis.

Premise of the study Free-living sperm of mosses are known to be partially desiccation tolerant. We hypothesized that mature moss antheridia should also tolerate desiccation and that rehydration to partial turgor (prehydration) or rehydration to full turgor (rehydration) before immersion in water is required for full recovery from any damaging effects of prior desiccation. Methods Bryum argenteum (silvery-thread moss) was grown in continuous culture for several months, produced mature perigonia (clusters of antheridia), and these were subjected to a slow rate of drying (∼36 h from full turgor to desiccation) and equilibration with 50% relative humidity. Perigonia were prehydrated (exposed to a saturated atmosphere) or rehydrated (planted upright in saturated media) for 0, 45, 90, 135, 180, and 1440 min, then immersed in sterile water. Time to first sperm mass release, number of antheridia releasing sperm masses, and the integrity of the first sperm mass released were assessed. Key results Rehydration of dried antheridia for at least 3 h before immersion in water resulted in antheridia functioning similar to control undried antheridia. Compared with rehydration, prehydration was not effective in the recovery of antheridia from desiccation. Conclusions For the first time, moss antheridia are shown to be fully desiccation tolerant at a functional level, capable of releasing fully functional sperm following a slow drying event provided the antheridia are allowed to rehydrate at least 3 h before immersion in water.

Female plants of the moss Syntrichia caninervis are more common than male plants and are found in more thermally stressful habitats than male plants. We hypothesized that this distribution pattern is due to a more favorable regeneration response of females to thermal stress compared to that of males. Hydrated leaves from four genotypes of both sexes of S. caninervis were exposed for 60 min under lighted conditions to temperatures of 20, 30, 35, 40, and 45°C. Leaves were allowed to regenerate on native sand under recovery conditions (12-h photoperiod, 20°C lighted, and 8°C dark) for 56 days, and over this period, protonemal emergence, growth rate, and shoot production were assessed. Leaves exposed to higher heat shocks produced protonemata significantly later, exhibited significantly reduced growth rates over the course of the experiment, and produced fewer shoots but did not differ in the probability of producing a shoot. Males tended to produce protonemata earlier than females at the highest thermal stress, whereas females tended to produce protonemata earlier under control conditions. Female leaves regenerated at twice the rate of male leaves, producing twice the area of protonemal cover; this gender difference was lessened at the highest thermal stress. Female leaves regenerated significantly more shoots than males, with each sex exhibiting different peaks of shoot production depending on the thermal stress. No interaction effect was detectable between gender and stress treatment. While females had a more favorable regeneration response relative to males, thermal stress diminished this difference, thus suggesting that our hypothesis was not supported.

Spatial variation in population sex ratios is common in bryophytes, but the ecological correlates of this variation are not well documented. The dioecious desert moss Syntrichia caninervis presents an example of this variation occurring at the regional scale (kilometers) as well as the microscale (centimeters). Here, our goal is to correlate variation in plant traits and sex expression levels to relevant ecological variation, and specifically to investigate whether spatial segregation of the sexes (SSS) exists at the level of the patch. Five sporophytic patches of S. caninervis were sampled at 10 cm intervals along a transect extending from shrub understory into the exposed intershrub region, thus representing a stress gradient of light intensity and moisture availability. Along a gradient from understory to intershrub microsites, individual plant length and biomass declined significantly, with plants under the canopy twice as large as those in the more exposed microsites. Sex expression declined...

Disparate sex ratios are a widespread pattern in dioecious bryophytes, with female‐biased ratios especially prevalent in arid environments. The absence of male plants in environments experiencing high desiccation pressure prompted the hypothesis that male plants may be less desiccation tolerant than female plants in the desert moss Syntrichia caninervis. This hypothesis was investigated by exposing detached leaves to consecutive wet/rapid‐dry treatments and monitoring viability, protonemal emergence time, shoot production, growth rate of secondary protonemata, and microbial infection frequency over a 56‐d period. The desiccation treatment consisted of exposure of mature 1‐yr‐old leaves to zero, two, four, and six wet/rapid‐dry cycles. Hydrated leaves were then allowed to regenerate. Desiccation stress level was significantly correlated to reduced protonemal emergence, reduced growth rates, and reduced shoot production. Female detached leaves produced protonemata more quickly, and these protonemata grew tw...

Ten sporophytic populations of Syntrichiacaninervis contained an average of 22 individualscm−2, with a sex ratio of 7.9 Female:1 Male: 3.1 Nonexpressing(N = 300). In each of the populations, female individuals outnumberedmale individuals. A representative population size of 50 × 25cm was estimated to contain 27,250 organically distinct individualplants. Given the wide disparity in reproductive investment in this dioeciousspecies, sex-specific traits were investigated at the level of the individualinbiomass, total stem length, number of ramets, number of branches, length ofannual growth interval, length of longest ramet, age, number of inflorescences,number of ramets expressing sex, and consecutive seasons of sex expression. Theonly significant sex dimorphism recorded was in consecutive seasons of sexexpression, with nonsporophytic female individuals exhibiting a higherfrequencythan males. However, nonexpressing individuals had lower biomass, shorter totalstem length, fewer branches, and shorter ramets than males and females, andfewer ramets than female individuals. When the biomass of female and maleindividuals was controlled for inflorescence number, no significant differencesbetween the sexes in biomass were found. There appears to be a threshold sizefor sex expression, with all individuals above 2.0 mg dry weightexpressing sex (N = 108). Biomass and total stem length are strongpositive correlates (r = 0.88), and individual biomass is a betterpredictor of the number of inflorescences produced per individual than is stemlength (r = 0.85 vs. r = 0.69, respectively). Independent of stemlength, individual biomass had a positive and significant relationship withinflorescence number; however, independent of individual biomass, stem lengthwas not associated with inflorescence number. Overall sex expression was 0.74(individual level) and 0.65 (ramet level). The functional sex ratio wasassessedat the inflorescence level, and ranged from 9.7♀:1♂, to14.9♀:1♂ over the most recent four years. Fertilization frequencywas 0.69 (individual level) and 0.34 (perichaetial level). Over the last threeyears, 63% of all fertilized perichaetia resulted in an abortivesporophyte.

The desert moss Syntrichia caninervis exhibits one of the most skewed sex ratios in the plant kingdom, with female individuals far outnumbering male individuals (exceeding 14♀:1♂). The "cost of sex hypothesis" derives from allocational theory and predicts that the sex which is most expensive should be the rarer sex. This hypothesis, which, as considered here represents the realized cost of sexual reproduction, is contingent upon two assumptions that are explored: (1) that male sex expression is more expensive than female sex expression, and (2) that sexual reproduction is resource limited. Using inflorescence biomass and discounting sperm, male sex expression was found to be in the neighborhood of one order of magnitude more expensive than female sex expression, and this difference is reflected in higher numbers of gametangia per male inflorescence, presence of paraphyses in male inflorescences, and a much longer developmental time for male inflorescences. The realized cost of female reproduction from two communities dominated by S. caninervis was found to be lower than the realized cost of male sexual reproduction. Resource-limited reproduction was assessed by determining the frequency of sporophyte abortion, the age distribution of sporophyte abortions, and patterns of sporophyte abortion that may be density dependent. Among ten sexually reproducing populations, abortive sporophytes occurred at a frequency of 0.64. Abortive sporophytes averaged 8% the mass of mature sporophytes, and cohort sporophytes from the same individual female were found to abort in a density-dependent pattern. We conclude that the two assumptions, upon which the cost of sex hypothesis depends, are supported.

The moss Syntrichia caninervis is the dominant soil bryophyte in a blackbrush (Coleogyne ramosissima) community in the southern Nevada Mojave Desert, with a mean cover of 6.3%. A survey of the 10-ha study site revealed an expressed ramet sex ratio of 14 / :1 ? (N 5 890), with 85% of ramets not expressing sex over their life span, and an expressed population sex ratio of 40/ :2 ? :1 /? (female : male : mixed-sex, N 5 89), with 52% of populations not expressing sex. A greater incidence of sex expression was associated with shaded microsites, higher soil moisture content, and taller ramets. Shaded microsites had higher surface soil moisture levels than exposed microsites. In the exposed microhabitat, surface soil moisture was positively correlated with ramet height but not with sex expression. Male ramets and populations were restricted to shaded microhabitats, whereas female ramets and populations were found in both shaded and exposed microhabitats, suggesting gender specialization. The rarity of mature sporophytes, found in 0% of the ramets sampled and in only 3% of the populations, is probably due to the rarity of mixed-sex populations. We hypothesize that mixed-sex populations are rare because of factors relating to male rarity and that the differential cost of sex expression reduces the clonal growth capacity of male individuals.

The extremely skewed female-biased sex ratio in the desert moss Syntrichia caninervis was investigated by assessing the regeneration capacity of detached leaves. Juvenile, green, yellow-green, and brown leaves equating to approximately 0, 2, 6, and 12 yr of age, respectively, were detached from individuals of S. caninervis collected from 10 field populations and grown in a growth chamber for 58 d at a light intensity of 33-128 μmol · m(-2) · s(-1). Younger leaves (0-2 yr old) tended to have a greater viability, regenerate more quickly, extend their protonemal filaments farther, produce shoots (gametophores) more quickly, produce more shoots, and accumulate a greater biomass than older leaves (6 and 12 yr old). Among younger leaf classes, regenerating female leaves were more likely to produce a shoot than male leaves and produced more shoots than male leaves. The sexes did not differ significantly in time until protonemal emergence, linear extension of protonemata, or rate of biomass accumulation. However, protonemata of male leaves tended to emerge more quickly and produce a greater total biomass, ultimately consisting mostly of protonemata, than did female leaves. The more rapid proliferation of shoots by female leaf regenerants may help to explain the rarity of males in this species.

†Background and Aims Expected life history trade-offs associated with sex differences in reproductive investment are often undetected in seed plants, with the difficulty arising from logistical issues of conducting controlled experiments. By controlling genotype, age and resource status of individuals, a bryophyte was assessed for sexspecific and location-specific patterns of vegetative, asexual and sexual growth/reproduction across a regional scale. †Methods Twelve genotypes (six male, six female) of the dioecious bryophyte Bryum argenteum were subcultured to remove environmental effects, regenerated asexually to replicate each genotype 16 times, and grown over a period of 92 d. Plants were assessed for growth rates, asexual and sexual reproductive traits, and allocation to above- and below-ground regenerative biomass. †Key Results The degree of sexual versus asexual reproductive investment appears to be under genetic control, with three distinct ecotypes found in this study. Protonemal growth rate was positively correlated with asexual reproduction and sexual reproduction, whereas asexual reproduction was negatively correlated (appeared to trade-off ) with vegetative growth (shoot production). No sex-specific trade-offs were detected. Female sexexpressing shoots were longer than males, but the sexes did not differ in growth traits, asexual traits, sexual induction times, or above- and below-ground biomass. Males, however, had much higher rates of inflorescence production than females, which translated into a significantly higher (24x) prezygotic investment for males relative to females. †Conclusions Evidence for three distinct ecotypes is presented for a bryophyte based on regeneration traits. Prior to zygote production, the sexes of this bryophyte did not differ in vegetative growth traits but significantly differed in reproductive investment, with the latter differences potentially implicated in the strongly biased female sex ratio. The disparity between males and females for prezygotic reproductive investment is the highest known for bryophytes.

†Background and Aims Active growth in post-embryonic sporophytes of desert mosses is restricted to the cooler, wetter months. However, most desert mosses have perennial gametophytes. It is hypothesized that these life history patterns are due, in part, to a reduced desiccation tolerance for sporophytes relative to gametophytes. †Methods Gametophytes with attached post-embryonic sporophytes of Tortula inermis (early seta elongation phenophase) were exposed to two levels of desiccation stress, one rapid-dry cycle and two rapid-dry cycles, then moistened and allowed to recover, resume development, and/or regenerate for 35 d in a growth chamber. †Key Results Gametophytes tolerated the desiccation treatments well, with 93 % survival through regenerated shoot buds and/or protonemata. At the high stress treatment, a significantly higher frequency of burned leaves and browned shoots occurred. Sporophytes were far more sensitive to desiccation stress, with only 23 % surviving after the low desiccation stress treatment, and 3 % surviving after the high desiccation stress treatment. While the timing of protonemal production and sporophytic phenophases was relatively unaffected by desiccation stress, shoots exposed to one rapid-dry cycle produced shoots more rapidly than shoots exposed to two rapid-dry cycles. †Conclusions It is concluded that sporophytes of Tortula inermis are more sensitive to rapid drying than are maternal gametophytes, and that sporophyte abortion in response to desiccation results from either reduced desiccation tolerance of sporophytes relative to gametophytes, or from a termination of the sporophyte on the part of the gametophyte in response to stress.

Actively growing post-embryonic sporophytes of desert mosses are restricted to the cooler, wetter months. However, most desert mosses have perennial gametophytes. It is hypothesized that these life history patterns are due in part to a reduced thermotolerance for sporophytes relative to gametophytes.Gametophytes with attached embryonic sporophytes of Microbryum starckeanum were exposed whilst desiccated to thermal episodes of 35 degrees C (1 hr), 55 degrees C (1 hr), 75 degrees C (1 hr) and 75 degrees C (3 hr), then moistened and allowed to recover for 35 d in a growth chamber.All of the gametophytes survived the thermal exposures and produced protonemata, with the majority also producing shoot buds. Symptoms of gametophytic stress (leaf burning and discoloration of entire shoots) were present in lower frequencies in the 55 degrees C exposure. Sporophyte resumption of growth and maturation to meiosis were significantly negatively affected by thermal treatment. Not a single sporophyte exposed to the two higher thermal treatments (75 degrees C for 1 h and 75 degrees C for 3 h) survived to meiosis, and those sporophytes exposed to 75 degrees C that survived to the post-embryonic phenophase took significantly longer to reach this phase. Furthermore, among the thermal treatments where some capsules reached maturity (35 degrees C and 55 degrees C), maternal shoots that produced a meiotic capsule took longer to regenerate through protonemata than maternal shoots aborting their sporophyte, suggestive of a resource trade-off between generations.Either (1) the inherent sporophyte thermotolerance is quite low even in this desert moss, and/or (2) a gametophytic thermal stress response controls sporophyte viability.