Lloyd R. Stark

Gemma germination is known to require light in bryophytes. Water-dispersed (hydrochory) species, however, have not been tested for a light response, and one hypothesis is that hydrochory may be ecologically correlated with a burial response (dark germination of stolons capable of surfacing when buried). The eventual burial of floating propagules in muddy soil is likely to be frequent and thereby select for the ability to surface from depth. We found that the widespread often hydrochorous species Gemmabryum dichotomum produces protonemal (chloronemal) bulbils that (1) germinate in total darkness by producing negatively gravitropic or lateral rhizoidal stolons, (2) regerminate with protonemal filaments when subsequently exposed to light, (3) surface from sand burial depths of 4, 8, and 12 mm (grain size < 355 µm) and produce a surface colony of shoots and protonemal bulbils in 6–17 wk depending on burial depth, and (4) can tolerate at least 2 mos. of continuous darkness followed by regermination through protonemata when brought into the light. Prolonged darkness (2 mos.) resulted in delayed regermination, fewer protonemal filaments, and fewer shoots when brought into the light. However, such bulbils produced a greater protonemal spread than control bulbils due to protonemata arising from stolons previously produced in darkness.

El musgo recientemente descrito Gemmabryum brassicoides es común en regiones propensas a incendios en California (EE. UU.), y observaciones de campo indican que algunas poblaciones son capaces de sobrevivir al menos a ciertos incendios. Brotes desecados de esta especie, recolectados en campo, fueron expuestos a temperaturas de 100 °C a 130 °C durante 20 min y se les permitió regenerarse durante 21 días. La supervivencia de los brotes fue cercana al 100% tras la exposición a 100 °C y 110 °C, disminuyendo al 76% a 120 °C, 9% a 125 °C y 0% a 130 °C. Los brotes prehidratados se regeneraron a un nivel mucho mayor (2×) que los no prehidratados en las dos temperaturas más altas toleradas (120 y 125 °C). La disminución en el vigor regenerativo se observó únicamente en exposiciones ≥120 °C, según lo medido por los días hasta la primera regeneración, el número total de brotes regenerativos producidos y el porcentaje de superficies de brotes que regeneran. La regeneración a temperaturas más altas se produjo principalmente en las regiones subterráneas de los brotes. La capacidad de tolerar una exposición de 20 min a 125 °C convierte a G. brassicoides en la tercera especie vegetal conocida capaz de sobrevivir a una exposición de 120 °C (las otras dos son Bryum argenteum y Syntrichia caninervis) y en el primer ser vivo eucariota adulto conocido que sobrevive a una exposición de 20 min a 125 °C, lo que podría representar una adaptación para resistir los frecuentes incendios del chaparral californiano.

The desiccation tolerance of the spores of the model moss Physcomitrium patens is largely unknown. An opportunity arose to test spore longevity in P. patens capsules stored in near-darkness under laboratory conditions at low relative humidity (RH) levels for up to 11 years. Most of the capsules had slowly dried over a period of weeks as intact cultures in a growth chamber at high humidity. After this initial drying, the cultures with capsules were placed in the dark or at very dim lighting at (1) ambient relative humidity averaging 35% for periods up to 7 years, or (2) at 0% RH (one culture and a few separated sporophytic shoots) for up to 11 years. Germination was high (≥ 92%) for spores stored at ~35% for up to 5 years, dropping precipitously to 68% and < 15% in years 6 and 7, respectively. After experiencing periods of 5 and 11 years desiccation at equilibrating RHs of ~0%, spores of P. patens became nonvi­able except for a small percentage (< 2%) of spores only from closed capsules desiccated continuously for 11 years. Although spores of P. patens are on the large side for mosses with presumably greater storage reserves, toleration of dry dark periods longer than 7 years in open capsules is unlikely. Prehydration (exposing spores to humid air prior to added water), had no effect on spore germination through 7 years of desiccation, although for the oldest spores tested with open capsules (7 years), prehydration improved viability from 6 to 22%.

Premise: Mosses provide many ecosystem functions and are the most vulnerable of biocrust organisms to climate change due to their sensitive water relations stressed by summer aridity. Given their small size, moss stress resistance may be more dependent on fine‐scale habitat than macroclimate, but the sheltering role of habitat (i.e., habitat buffering) has never been compared to macroclimate and may have important implications for predicting critical biocrust moss refugia in changing climates.Methods: We located three populations of a keystone biocrust moss, Syntrichia caninervis, spanning 1200 m of altitude, which comprised three macroclimate (elevation) zones of characterized plant communities in the Mojave Desert. We stratified 92 microsites along three aridity gradients: elevation zone, topography (aspect), and microhabitat (shrub proximity). We estimated summer photosynthetic stress (F_v/F_m) and aridity exposure (macroclimate, irradiance, and shade).Results: Microsite aridity exposure varied greatly, revealing exposed and buffered microhabitats at all three elevation zones. Moss stress did not differ by elevation zone despite the extensive macroclimate gradient, failing to support the high‐elevation refugia hypothesis. Instead, stress was lowest on northerly‐facing slopes and in microhabitats with greater shrub shading, while the importance of (and interactions between) topography, irradiance, and shade varied by elevation zone.Conclusions: Fine‐scale habitat structure appears physiologically more protective than high‐elevation macroclimate and may protect some biocrust mosses from the brunt of climate change in widespread microrefugia throughout their current ranges. Our findings support a scale‐focused vulnerability paradigm: microrefugia may be more important than macrorefugia for bolstering biocrust moss resistance to summer climate stress.

Tuber viability was assessed in seven collections of Rosulabryum capillare from four Mojave Desert (USA) localities that had been stored desiccated in the dark for 25–30 years under conditions of low relative humidity (approximately 35% at approximately 23°C). While all 7 of the collections had at least two germinating tubers and 20% of tubers germinated overall, most of the viable tubers were from three collections, with one 25-year old set of tubers exhibiting 100% germination. The maximum duration dry found was 30 years and 6 months for six tubers from the Eldorado Mts, Nevada, USA. Tubers 28 years old were cultured to mature female plants in single clone cultures that produced germinable tubers of G. capillare after a year. Germination of tubers after 30 years of desiccation is consistent with earlier longevity reports, and may be near the ceiling of survival for bryophyte tubers.

Tubers are described for the first time in the moss genus Timmiella (Pottiaceae). Using uniclonal cultures, tubers were produced after at least 3 months, were spherical, often occurred in groups (“nests”), ranged in size from 10–600 µm in diameter, and had a water content of ∼4% (dry wt basis) while yet retaining an oil-like residue. On a per individual shoot basis, belowground biomass in cultures equaled aboveground biomass. Tubers germinated in ∼3 days from planting by producing multiple protonemal filaments, similar to detached shoot tips and rhizoids, but much more rapidly than detached leaves. Germinated tubers eventually formed a colony (producing 50 protonemal shoots and extending horizontally 11 mm) in ∼30 days, measures very similar to detached shoot tips, and faster than rhizoids and detached leaves. The presence of Timmiella crassinervis in frequently burned regions of chaparral suggests fire frequency in California may have selected for greater belowground allocation.

Collections of 36 species of predominantly low elevation Mojave Desert bryophytes from the mid-1990s were assessed for shoot and spore viability. Adult shoots of 16 (of 36) and spores of 14 (of 25) desert species were capable of germination or regeneration after 28 years of continuous desiccation (dark storage) under conditions of ∼23°C and 25–45% relative humidity. Most of the species found viable were in the families Pottiaceae and Grimmiaceae, but also included species of Bryum, Funaria and Ptychostomum. Both shoots and spores from the same collection (patch) of 9 species were viable, including Funaria hygrometrica, regarded in other habitats as an annual species. The oldest collection found viable was from shoots of Grimmia anodon, 29 yr 3 mos. Based on the vigor of shoot and spore regeneration/ germination observed in several species, the records presented here for desiccation longevity should be exceeded in the future.

Premise: Mosses provide many ecosystem functions and are the most vulnerable of biocrust organisms to climate change due to their sensitive water relations stressed by summer aridity. Given their small size, moss stress resistance may be more dependent on fine-scale habitat than macroscale (climate and community), but this sheltering role of habitat (i.e. habitat buffering) has never been compared to macroclimate and may have important implications for predicting critical biocrust refugia in changing climates. Methods: We located three populations of a keystone biocrust moss, Syntrichia caninervis , spanning 1200-m of altitude comprising three plant communities (elevation-plant zones) in the Mojave Desert. We stratified 96 microsites along three habitat aridity gradients: elevation-zone, topography (aspect), and microhabitat (shrub proximity). We estimated summer photosynthetic stress (F _v /F _m ) and aridity exposure (macroclimate, irradiance, and shade). Results: Microsite aridity exposure varied greatly revealing exposed and buffered microhabitats in all elevation-zones. Moss stress did not differ by elevation zone despite the extensive macroclimate gradient, failing to support the high-elevation refugia hypothesis. Instead, stress was lowest on N-facing slopes and microhabitats with higher shrub shading, while the importance of (and interactions between) topography, irradiance, and shade varied by elevation zone. Conclusions: We demonstrate fine-scale habitat buffering is physiologically more protective than high-elevation climate, and thus, may allow some mosses to hide from the brunt of climate change in widespread microrefugia throughout their current ranges. Our findings support a scale-focused vulnerability paradigm: microrefugia may be more important than macrorefugia for bolstering biocrust moss resistance to summer climate stress.

Premise: In dioicous mosses, sex is determined by a single U (female, ♀) or V (male, ♂) chromosome. Although a 1 : 1 sex ratio is expected following meiosis, phenotypic sex ratios based on the production of gametangia are often female‐biased. The dryland moss Syntrichia caninervis (Pottiaceae) is notable for its low frequency of sex expression and strong phenotypic female bias. Here we present a technique to determine genotypic sex in a single shoot of S. caninervis, and report results of a case study examining genotypic and phenotypic sex ratios.Methods: We reanalyzed 271 non‐expressing gametophyte shoots from a previous study on S. caninervis sex expression across microhabitats using a restriction fragment length polymorphism (RFLP) method.Results: We recovered a genotypic sex ratio in non‐expressing shoots of 18.4♀ : 1♂, which exceeds the female bias of the phenotypic ratio (5.3♀ : 1♂; P = 0.013). We also found that the distribution of male and female genotypes across microsites with different levels of sun exposure was not predicted by patterns of sex expression in these microsites.Discussion: These findings contribute to our understanding of how the environment may modulate sex ratios in S. caninervis, either through its direct influence on sex expression or through selection on genotypes with particular sex expression phenotypes.