Impact of changing climate on bryophyte contributions to terrestrial water, carbon, and nitrogen cycles.

Bryophytes, including the lineages of mosses, liverworts, and hornworts, are the second-largest photoautotroph group on Earth. Recent work across terrestrial ecosystems has highlighted how bryophytes retain and control water, fix substantial amounts of carbon (C), and contribute to nitrogen (N) cycles in forests (boreal, temperate, and tropical), tundra, peatlands, grasslands, and deserts. Understanding how changing climate affects bryophyte contributions to global cycles in different ecosystems is of primary importance. However, because of their small physical size, bryophytes have been largely ignored in research on water, C, and N cycles at global scales. Here, we review the literature on how bryophytes influence global biogeochemical cycles, and we highlight that while some aspects of global change represent critical tipping points for survival, bryophytes may also buffer many ecosystems from change due to their capacity for water, C, and N uptake and storage. However, as the thresholds of resistance of bryophytes to temperature and precipitation regime changes are mostly unknown, it is challenging to predict how long this buffering capacity will remain functional. Furthermore, as ecosystems shift their global distribution in response to changing climate, the size of different bryophyte-influenced biomes will change, resulting in shifts in the magnitude of bryophyte impacts on global ecosystem functions.

Phenology and foraging bias contribute to sex-specific foraging patterns in the rare declining butterfly Argynnis idalia idalia.

Variation in pollinator foraging behavior can influence pollination effectiveness, community diversity, and plant-pollinator network structure. Although effects of interspecific variation have been widely documented, studies of intraspecific variation in pollinator foraging are relatively rare. Sex-specific differences in resource use are a strong potential source of intraspecific variation, especially in species where the phenology of males and females differ. Differences may arise from encountering different flowering communities, sex-specific traits, nutritional requirements, or a combination of these factors. We evaluated sex-specific foraging patterns in the eastern regal fritillary butterfly (Argynnis idalia idalia), leveraging a 21-year floral visitation dataset. Because A. i. idalia is protandrous, we determined whether foraging differences were due to divergent phenology by comparing visitation patterns between the entire season with restricted periods of male-female overlap. We quantified nectar carbohydrate and amino acid contents of the most visited plant species and compared those visited more frequently by males versus females. We demonstrate significant differences in visitation patterns between male and female A. i. idalia over two decades. Females visit a greater diversity of species, while dissimilarity in foraging patterns between sexes is persistent and comparable to differences between species. While differences are diminished or absent in some years during periods of male-female overlap, remaining signatures of foraging dissimilarity during implicate mechanisms other than phenology. Nectar of plants visited more by females had greater concentrations of total carbohydrates, glucose, and fructose and individual amino acids than male-associated plants. Further work can test whether nutritional differences are a cause of visitation patterns or consequence, reflecting seasonal shifts in the nutritional landscape encountered by male and female A. i. idalia. We highlight the importance of considering sex-specific foraging patterns when studying interaction networks, and in making conservation management decisions for this at-risk butterfly and other species exhibiting strong intraspecific variation.

Species-specific interactions in avian-bryophyte dispersal networks.

Studies from seed plants have shown that animal dispersal fundamentally alters the success of plant dispersal, shaping community composition through time. Our understanding of this phenomenon in spore plants is comparatively limited. Though little is known about species-specific dispersal relationships between passerine birds and bryophytes, birds are particularly attractive as a potential bryophyte dispersal vector given their highly vagile nature as well as their association with bryophytes when foraging and building nests. We captured birds in Gifford Pinchot National Forest to sample their legs and tails for bryophyte propagules. We found 24 bryophyte species across 34 bird species. We examined the level of interaction specificity: (i) within the overall network to assess community level patterns; and (ii) at the plant species level to determine the effect of bird behaviour on network structure. We found that avian-bryophyte associations are constrained within the network, with species-specific and foraging guild effects on the variety of bryophytes found on bird species. Our findings suggest that diffuse bird-bryophyte dispersal networks are likely to be common in habitats where birds readily encounter bryophytes and that further work aimed at understanding individual bird-bryophyte species relationships may prove valuable in determining nuance within this newly described dispersal mechanism.

Species-specific effects of passive warming in an Antarctic moss system.

Polar systems are experiencing rapid climate change and the high sensitivity of these Arctic and Antarctic ecosystems make them especially vulnerable to accelerated ecological transformation. In Antarctica, warming results in a mosaic of ice-free terrestrial habitats dominated by a diverse assemblage of cryptogamic plants (i.e. mosses and lichens). Although these plants provide key habitat for a wide array of microorganisms and invertebrates, we have little understanding of the interaction between trophic levels in this terrestrial ecosystem and whether there are functional effects of plant species on higher trophic levels that may alter with warming. Here, we used open top chambers on Fildes Peninsula, King George Island, Antarctica, to examine the effects of passive warming and moss species on the abiotic environment and ultimately on higher trophic levels. For the dominant mosses, Polytrichastrum alpinum and Sanionia georgicouncinata, we found species-specific effects on the abiotic environment, including moss canopy temperature and soil moisture. In addition, we found distinct shifts in sexual expression in P. alpinum plants under warming compared to mosses without warming, and invertebrate communities in this moss species were strongly correlated with plant reproduction. Mosses under warming had substantially larger total invertebrate communities, and some invertebrate taxa were influenced differentially by moss species. However, warmed moss plants showed lower fungal biomass than control moss plants, and fungal biomass differed between moss species. Our results indicate that continued warming may impact the reproductive output of Antarctic moss species, potentially altering terrestrial ecosystems dynamics from the bottom up. Understanding these effects requires clarifying the foundational, mechanistic role that individual plant species play in mediating complex interactions in Antarctica's terrestrial food webs.

Forest passerines as a novel dispersal vector of viable bryophyte propagules.

Animal dispersal influences the community structure and diversity of a wide variety of plant taxa, yet the potential effects of animal dispersal in bryophytes (hornworts, liverworts, and mosses) is poorly understood. In many communities, birds use bryophyte-abundant niche space for foraging and gathering nest material, suggesting that birds may play a role in bryophyte dispersal. As highly motile animals with long migratory routes, birds potentially provide a means for both local and long-distance bryophyte dispersal in a manner that differs greatly from passive, aerial spore dispersal. To examine this phenomenon, we collected and germinated bryophyte propagules from the legs, feet and tails of 224 birds from 34 species within a temperate forest community. In total we found 1512 spores, and were able to germinate 242 bryophyte propagules. In addition, we provide evidence that topical (externally-carried) spore load varies by bird species and behaviour. Tail feather spore abundance is highest in bark and foliage gleaning species and is positively correlated with tarsal length. Together, these data suggest that a variety of forest birds exhibit the potential to act as dispersal vectors for bryophyte propagules, including an abundance of spores, and that understanding the effects of animal behaviour on bryophyte dispersal will be key to further understanding this interaction.

Rapid population sex-ratio changes in the moss Ceratodon purpureus.

PREMISE OF THE STUDY: Sex-ratio variation occurs widely in dioecious plants, but the mechanisms of population sex-ratio bias are poorly understood. In bryophytes, sex ratios are often female biased, and little information is available about how and when bias forms. METHODS: To test whether population sex-ratio variation can emerge during the gametophytic phase and is not purely a product of spore sex ratios, we created artificial populations of the moss Ceratodon purpureus, with male- and female-biased sex ratios, and placed half under a stress treatment. We hypothesized that male-majority populations would become female-biased and that stress would increase this transition. After 18 mo, when sporophytes were initially forming, we used sex-specific molecular markers to determine population sex ratios. KEY RESULTS: Female-majority populations did not differ significantly from their original bias, whereas male-majority populations became significantly more female biased. The plants had only just produced their first spores, so these sex-ratio changes occurred during the gametophytic generation, as a result of sex-specific growth or survival. Sporophytes occurred only in populations with female-biased final sex ratios, which suggests that females in male-majority populations may have invested energy in ramets rather than in sporophyte production. The stress treatment was mild and had no effect on sex ratio. CONCLUSIONS: Our results suggest that female bias can be generated during the gametophytic generation, before plants reach sexual maturity. These results, combined with those of previous work, suggest that both the gametophytic and the sporophytic stages drive population sex ratios in C. purpureus, thus indicating that multiple mechanisms operate to create biased population sex ratios.