Effects of leaf hair points of a desert moss on water retention and dew formation: implications for desiccation tolerance

Enhancing fog harvesting efficiency with a multi-object-coupled bio-inspired surface

The global freshwater crisis poses a substantial threat to sustainable development, driving urgent demand for advanced atmospheric water harvesting technologies. While bio-inspired fog collectors have shown potential, conventional single-scale architectures often exhibit suboptimal performance due to inadequate coordination between droplet nucleation and transport. Here we present a multi-object-coupled venation-shaped patterned surface (MVSS) fabricated through laser-etching of filter paper/polydimethylsiloxane composite films. By synergistically integrating three bio-inspired mechanisms: (i) heterogeneous wettability patterns mimicking desert beetle elytra, (ii) conical spine arrays inspired by Opuntia histophysiology, and (iii) hierarchical venation networks derived from plant leaf, we establish a multi-stage phase-transition process that enhances fog harvesting efficiency through coordinated surface energy gradients and Laplace pressure modulation. The wettability contrast enables selective droplet nucleation, while the conical geometry generates asymmetric contact line pinning that drives directional transport. The hierarchical branching network minimizes hydraulic resistance through optimized flow path partitioning, achieving rapid drainage while suppressing edge water accumulation. This multi-scale synergy yields a record water collection rate of 1033 ± 28.2 mg cm-2 h-1. Our findings elucidate the critical role of structure-property coordination in fog water collection, providing a generalized design paradigm for developing high-efficiency atmospheric water harvesters. The fabrication strategy combining scalable laser processing with bio-composite materials suggests promising pathways for arid region deployment.

Insights into the adaptive response of extremotolerant desert moss Syntrichia caninervis to extreme high temperature

Moss has remarkable abilities to survive harsh environmental conditions, making it a key species in habitat restoration following disturbances such as fire, exploring these abilities informs efforts to improve stress tolerance in other plants and enhances our understanding of the evolution of stress tolerance. Here, we report a new record of thermal tolerance for the dried moss Syntrichia caninervis. Dry moss cuttings survived 60 min at 120 °C, exceeding the previous record of 30 min at 120 °C. We also investigated the morphology and gene expression profile of the shoots from dried S. caninervis shoots exposed to 80, 100, 110, and 120 °C for 10, 20, 30, or 60 min, using 20 °C as the control temperature. Shoots were allowed to regenerate on native sand under recovery conditions, after which we examined them daily for 56 days. Over this period, our observations indicated that lethal time-temperature combinations abolished shoot regeneration potential, whereas sub-lethal combinations lengthened the emergence time of protonema and new shoots, and led to decreased protonema emergence area. In addition, we determined that the transcript levels of nine genes (ScHSP70-3, ScHSP70-12, ScHSP70-15, ScELIP1, ScELIP2, ScABA1, ScABA3, ScNCED, and ScDREB) were induced upon temperature stress, as assessed following 120 °C 30 min of heat stress exposure. Few extant desert mosses encounter temperatures this high in nature, suggesting that the observed tolerance is unlikely to be the result of adaptation to current or recent climate conditions. We hope that the results of this study will help us understand the mechanisms by which organisms such as mosses survive thermal stress and how these mechanisms evolved.

Phenotypic plasticity of Eurohypnum leptothallum in degraded karst ecosystems: Adaptative mechanisms and ecological functions driven by warming temperatures

Phenotypic plasticity is a critical mechanism for plants to adapt to rapid climate change and other global change drivers. Eurohypnum leptothallum is widely distributed in fragile subtropical karst ecosystems, exhibiting strong drought tolerance, water retention, and soil stabilization capabilities, playing a vital ecological role in nutrient cycling and ecological restoration. Our study investigated the specific manifestations of phenotypic plasticity in epilithic E. leptothallum within degraded karst ecosystems. Results showed that E. leptothallum exhibited high phenotypic plasticity in the heterogeneous environments of degraded karst ecosystems. In the temperature range of 21.5 °C-59.5 °C, E. leptothallum developed a set of adaptive mechanisms in response to warming temperatures through the trade-offs and combinations in most morphological traits (increasing in shoot height, stem cortical ratio and leaf middle cell lumen area, decreasing in stem diameter and stem central strand ratio, making leaf shape, cell shape and lumen shape tend to ellipse) and physiological traits (increasing in C, Ca, C:N, C:P, N:P, Fv/Fm and Y(NO), decreasing in qP). Furthermore, these phenotypic variations may confer certain ecological benefits to the degraded karst ecosystems and are expected to contribute to the maintenance and sustainable development of structural stability and species diversity in degraded karst ecosystems and even global ecosystems in the early stages of global warming. The findings provide a new perspective for exploring the response of bryophytes to environmental changes, a theoretical basis for predicting the adaptive strategies of E. leptothallum and its potential ecological functions to degraded karst ecosystems under global warming.

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.

The dynamics of external water conduction in the dryland moss Syntrichia

Syntrichia relies on external water conduction for photosynthesis, survival, and reproduction, a condition referred to as ectohydry. Capillarity spaces are abundant in Syntrichia, but the link between function and morphology is complex. The aim of this study was to provide a better understanding of species-specific morphological traits underlying the functions of water conduction and storage. We used an environmental scanning electron microscope and confocal microscopy for observing anatomical characters in the leaves of Syntrichia species. We also measured hydration/dehydration curves to understand the rate of conduction and dehydration by experimental approaches. Syntrichia is an ectohydric moss that can externally transport and store water from the base of the stem using capillary action. We propose a new framework to study ectohydric capabilities, which incorporates three morphological scales and the timing of going from completely dehydrated to fully hydrated. Characters of interest in this model include cell anatomy (papillae development, hyaline basal cells and laminar cells), architecture of the stem (concavity and orientation) and whole clump characteristics (density of stems). We report significant variations in the speed of conduction, water holding capacity and hydration associated with each species studied (11 in total). All Syntrichia species are capable of external water conduction and storage, but the relevant traits differ among species. These results help to understand potential evolutionary and ecological trade-offs among speed of water conduction, water holding capacity, ontogeny, and differing habitat requirements. An integrative view of ectohydry in Syntrichia contributes to understanding the water relationships of mosses.

Diversity, phylogeny, and adaptation of bryophytes: insights from genomic and transcriptomic data

Bryophytes including mosses, liverworts, and hornworts are among the earliest land plants, and occupy a crucial phylogenetic position to aid in the understanding of plant terrestrialization. Despite their small size and simple structure, bryophytes are the second largest group of extant land plants. They live ubiquitously in various habitats and are highly diversified, with adaptive strategies to modern ecosystems on Earth. More and more genomes and transcriptomes have been assembled to address fundamental questions in plant biology. Here, we review recent advances in bryophytes associated with diversity, phylogeny, and ecological adaptation. Phylogenomic studies have provided increasing supports for the monophyly of bryophytes, with hornworts sister to the Setaphyta clade including liverworts and mosses. Further comparative genomic analyses revealed that multiple whole-genome duplications might have contributed to the species richness and morphological diversity in mosses. We highlight that the biological changes through gene gain or neofunctionalization that primarily evolved in bryophytes have facilitated the adaptation to early land environments; among the strategies to adapt to modern ecosystems in bryophytes, desiccation tolerance is the most remarkable. More genomic information for bryophytes would shed light on key mechanisms for the ecological success of these 'dwarfs' in the plant kingdom.

Ecology and responses to climate change of biocrust-forming mosses in drylands

Interest in understanding the role of biocrusts as ecosystem engineers in drylands has substantially increased during the past two decades. Mosses are a major component of biocrusts and dominate their late successional stages. In general, their impacts on most ecosystem functions are greater than those of early-stage biocrust constituents. However, it is common to find contradictory results regarding how moss interactions with different biotic and abiotic factors affect ecosystem processes. This review aims to (i) describe the adaptations and environmental constraints of biocrust-forming mosses in drylands, (ii) identify their primary ecological roles in these ecosystems, and (iii) synthesize their responses to climate change. We emphasize the importance of interactions between specific functional traits of mosses (e.g. height, radiation reflectance, morphology, and shoot densities) and both the environment (e.g. climate, topography, and soil properties) and other organisms to understand their ecological roles and responses to climate change. We also highlight key areas that should be researched in the future to fill essential gaps in our understanding of the ecology and the responses to ongoing climate change of biocrust-forming mosses. These include a better understanding of intra- and interspecific interactions and mechanisms driving mosses' carbon balance during desiccation-rehydration cycles.

Measuring volatile emissions from moss gametophytes: A review of methodologies and new applications

Mosses inhabit nearly all terrestrial ecosystems and engage in important interactions with nitrogen-fixing microbes, sperm-dispersing arthropods, and other plants. It is hypothesized that these interactions could be mediated by biogenic volatile organic compounds (BVOCs). Moss BVOCs may play fundamental roles in influencing local ecologies, such as biosphere-atmosphere-hydrosphere communications, physiological and evolutionary dynamics, plant-microbe interactions, and gametophyte stress physiology. Further progress in quantifying the composition, magnitude, and variability of moss BVOC emissions, and their response to environmental drivers and metabolic requirements, is limited by methodological and analytical challenges. We review several sampling techniques with various analytical approaches and describe best practices in generating moss gametophyte BVOC measures. We emphasize the importance of characterizing the composition and magnitude of moss BVOC emissions across a variety of species to better inform and stimulate important cross-disciplinary studies. We conclude by highlighting how current methods could be employed, as well as best practices for choosing methodologies.

Biocrust Research in China: Recent Progress and Application in Land Degradation Control

Desert ecosystems are generally considered lifeless habitats characterised by extreme environmental conditions, yet they are successfully colonised by various biocrust nonvascular communities. A biocrust is not only an important ecosystem engineer and a bioindicator of desert ecological restoration but also plays a vital role in linking surficial abiotic and biotic factors. Thus, extensive research has been conducted on biocrusts in critical dryland zones. However, few studies have been conducted in the vast temperate deserts of China prior to the beginning of this century. We reviewed the research on biocrusts conducted in China since 2000, which firstly focused on the eco-physiological responses of biocrusts to species composition, abiotic stresses, and anthropological disturbances. Further, research on the spatial distributions of biocrusts as well as their succession at different spatial scales, and relationships with vascular plants and soil biomes (especially underlying mechanisms of seed retention, germination, establishment and survival of vascular plants during biocrust succession, and creation of suitable niches and food webs for soil animals and microorganisms) was analysed. Additionally, studies emphasising on the contribution of biocrusts to ecological and hydrological processes in deserts as well as their applications in the cultivation and inoculation of nonvascular plants for land degradation control and ecological restoration were assessed. Finally, recent research on biocrusts was evaluated to propose future emerging research themes and new frontiers.

Freeze-thaw cycles change the physiological sensitivity of Syntrichia caninervis to snow cover

Spring, especially the freeze-thaw season, is considered the key period for the growth and carbon sequestration of desert mosses. It is not clear how the change in environment water and temperature affects the physiological characteristics of desert mosses in freeze-thaw season. In this study, the effects of water and freeze-thaw cycles on the physiological characteristics of Syntrichia caninervis were assessed by manipulating the increase or removal of 65% snow and changes in the freeze-thaw cycles. The results showed that the changes in snow depth, freeze-thaw cycles, and their interaction significantly affected the plant water content, osmoregulatory substances content, antioxidant substance, and antioxidant enzyme activities. The contents of free proline, soluble sugar, ascorbic acid (AsA), reduced glutathione (GSH), and malondialdehyde (MDA), and superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities increased significantly with the decrease in snow depth and freeze-thaw cycles. POD and free proline were the most sensitive to the snow depth and freeze-thaw cycles, while SOD and CAT were the least sensitive. Therefore, compared with the increase in freeze-thaw cycles, the reduction in freeze-thaw cycles weakened the physiological sensitivity of S. caninervis to snow depth changes.

External-field-induced directional droplet transport: A review

Directional transport of fluids is crucial for vital activities of organisms and numerous industrial applications. This process has garnered widespread research attention due to the wide breadth of flexible applications such as medical diagnostics, drug delivery, and digital microfluidics. The rational design of functional surfaces that can achieve the subtle control of liquid behavior. Previous studies were mainly dependent on the special asymmetric structures, which inevitably have the problem of slow transport speed and short distance. To improve controllability, researchers have attempted to use external fields, such as thermal, light, electric fields, and magnetic fields, to achieve controllable droplet transport. On the fundamental side, much of their widespread applicably is due to the degree of control over droplet transport. This review provides an overview of recent progress in the last three years toward the transport of droplets with different mechanisms induced by various external stimuli, including light, electric, thermal, and magnetic field. First, the relevant basic theory and typical induced gradient for directional liquid transport are illustrated. We will then review the latest advances in the external-field-induced directional transport. Moreover, the most emerging applications such as digital microfluidics, harvesting of energy and water, heat transfer, and oil/water separation are also presented. Finally, we will outline possible future perspectives to attract more researchers interest and promote the development of this field.

Geographic Pattern of Bryophyte Species Richness in China: The Influence of Environment and Evolutionary History

How contemporary environment interacts with macroevolutionary processes to generate the geographic pattern of bryophyte species is still unresolved. China is very rich in bryophytes, with more than 3,000 bryophytes covering 70% of the families in the world. In this study, we assessed the effects of the contemporary environment (average temperature of the coldest season TCQ, precipitation of the warmest season PWQ, and elevational range) and the recent diversification rates (estimated as mean species number per genus, MSG) on the geographical pattern of species richness for bryophytes and two groups (i.e., liverworts and mosses) in China. We compiled the provincial level distribution of bryophyte species and estimated the geographic pattern of the recent diversification rate by MSG for species in China. Univariate, multivariate regressions and path model analyses were used to assess the relationships between species richness, MSG, and their potential environmental drivers. Species richness of all bryophytes and liverworts significantly increased with the increase of MSG, either in regressions or path analyses, indicating that provinces with high bryophyte richness were mainly inhabited by species (especially liverworts) from lineages with particularly high MSG. In contrast, the species richness of mosses was insignificantly decreased with MSG in univariate regression or insignificantly increased with MSG in path analysis. Both species richness and MSG of all bryophytes and liverworts increased with the increase in energy and water availability. In contrast, for mosses, the species richness significantly increased with the increase of energy and water availability, while MSG decreased with the increase of energy and water availability. The MSG of liverworts increase with the increase of elevational range but the MSG of mosses decrease with the increase of elevational range. Our study suggests that the humid tropical and subtropical mountains in China are not only diversity hotspots for bryophytes, but also cradles for high recent diversification of liverworts, and refuges for mosses to hold many monotypic and oligotypic genera.

Influence of secondary metabolites on surface chemistry and metal adsorption of a devitalized lichen biomonitor

Despite the broad use of lichens as biomonitors of airborne trace elements, the surface chemistry and metal adsorption parameters of these organisms are still poorly known. The current investigation is aimed at (i) quantifying the acid-base surface properties and the first-order physical-chemical parameters of Cu2+ and Zn2+ adsorption of devitalized Pseudevernia furfuracea, a lichen commonly used in biomonitoring of airborne trace elements, and (ii) comparing the results with those available for moss biomonitors. Equilibrium constants and metal-binding site concentrations were calculated with a thermodynamic model by taking into account the presence/absence of ancillary extracellular cell wall compounds, namely melanin and acetone-soluble lichen substances. An acid-base titration experiment performed in the pH range of 3-10 showed that melanised and non-melanised P. furfuracea samples have lower pHPZC (3.53-3.99) and higher metal-binding site concentrations (0.96-1.20 mmol g-1) compared to that of the mosses investigated so far at the same experimental conditions. Melanin biosynthesis increased the content of carboxyl and phosphoryl groups and reduces that of amine/polyphenols. Cu2+ and Zn2+ adsorption was unaffected by the degree of melanisation while the removal of extracellular lichen substances slightly decreased Zn2+ adsorption. Although Cu2+ and Zn2+ adsorption parameters related to P. furfuracea surfaces were 3 times lower than in the mosses, lichen samples adsorbed the same amount of Cu2+ and 30% more Zn2+. The present study contributes in understanding the role of ancillary cell wall compounds in Cu2+ and Zn2+ adsorption in a model lichen. It also provides a first comparison between the surface physico-chemical characteristics of lichens and mosses frequently used as biomonitors of trace elements.

Moss-biocrusts strongly decrease soil surface albedo, altering land-surface energy balance in a dryland ecosystem

Land surface albedo measures the degree to which the sun's radiation is absorbed or reflected, and thus can be highly influential in global climate trends, local weather phenomena, and biological processes. As an extensive living cover in drylands, biocrusts cover substantial land surface but their potential influences on surface albedo and energy balance are underdocumented, and its temporal dynamic is virtually unknown. We continuously measured the surface albedo, land-surface energy balance, temperature and moisture of moss-biocrust covered soil and bare soil for two years, and measured the surface color and roughness of the two land cover types. Our results showed that the surface albedo of the biocrusts was 43.4% lower than that of the bare soil, due to the increased darkness (43.7%) and roughness (90.4%) together with increased moisture (20.7%) of the biocrust layer. Through time, the albedo of the biocrusts were negatively and linearly related with surface soil temperature or moisture, which resulted in lower albedo in summer and higher albedo in other seasons. As a result of decreased albedo, biocrusts decreased outgoing short-wave radiation by 44.8% in comparison to the bare soil, and consequently they increased net short-wave radiation by 11.4% and net all-wave solar radiation by 22.9% However, the increased energy absorption by the biocrusts did not consistently increase soil temperature; instead, soil temperature increased by up to 9.3 °C under dry conditions but decreased by as much as 11.4 °C under wet conditions, resulting in a net cooling. This indicates that the temperature regimes of the biocrust-covered soil were not determined only by albedo, but also by modification of soil thermal properties by biocrusts. Because biocrusts are highly responsive to land use, it appears that altered albedo and energy balance may be one of the ways in which human activity can impact climate and weather.

The pervasive and multifaceted influence of biocrusts on water in the world's drylands

The capture and use of water are critically important in drylands, which collectively constitute Earth's largest biome. Drylands will likely experience lower and more unreliable rainfall as climatic conditions change over the next century. Dryland soils support a rich community of microphytic organisms (biocrusts), which are critically important because they regulate the delivery and retention of water. Yet despite their hydrological significance, a global synthesis of their effects on hydrology is lacking. We synthesized 2,997 observations from 109 publications to explore how biocrusts affected five hydrological processes (times to ponding and runoff, early [sorptivity] and final [infiltration] stages of water flow into soil, and the rate or volume of runoff) and two hydrological outcomes (moisture storage, sediment production). We found that increasing biocrust cover reduced the time for water to pond on the surface (-40%) and commence runoff (-33%), and reduced infiltration (-34%) and sediment production (-68%). Greater biocrust cover had no significant effect on sorptivity or runoff rate/amount, but increased moisture storage (+14%). Infiltration declined most (-56%) at fine scales, and moisture storage was greatest (+36%) at large scales. Effects of biocrust type (cyanobacteria, lichen, moss, mixed), soil texture (sand, loam, clay), and climatic zone (arid, semiarid, dry subhumid) were nuanced. Our synthesis provides novel insights into the magnitude, processes, and contexts of biocrust effects in drylands. This information is critical to improve our capacity to manage dwindling dryland water supplies as Earth becomes hotter and drier.

Rupture of a Liquid Bridge between a Cone and a Plane

In this work, a systematic experimental study of the rupture of an axially symmetric liquid bridge between a cone and a plane was performed, with focus on the volume distribution after break up. A model based on the Young-Laplace equation is presented, and its solutions are compared to experimental data. Cones and conical cavities with different aperture angles were used in our experiments. We found that this aperture influences the potential pinning of the contact line, the meniscus shape, and therefore the liquid transfer. For half aperture angles α < 70°, where no pinning was observed, the liquid bridge slips off from the cone and almost no transfer to the cone is observed. However, at α > 70°, contact line pinning on the cone induces a net liquid transfer to the cone at rupture. In the case of conical cavities, a maximum of liquid transfer is observed for at α = 110°. The distance at which the rupture of the liquid bridge occurs is also discussed. The model can fairly predict the transfer ratio and the rupture height of the liquid bridge.

Impacts of the removal of shrubs on the physiological and biochemical characteristics of Syntrichia caninervis Mitt: in a temperate desert

Moss crusts play important roles in biological soil crusts biomass and soil surface stabilization. However, because of increasingly intensive human activities, especially grazing, the growth and survival of shrubs are seriously threatened. This study aimed to test whether the presence of shrubs affects the physiological state of the bryophyte Syntrichia caninervis Mitt. in this desert ecosystem. We simulated animal-grazed shrubs at three levels in the Gurbantunggut Desert and compared these simulations to exposed areas, measuring the indicators of growth and stress tolerance exhibited by bryophytes. The results showed that the removal of shrubs significantly decreased chlorophyll fluorescence activity and soluble protein content in S. caninervis, especially under the total shrub removal treatment. The ratio between the total removal of shrubs and other treatments in antioxidative enzymes and in osmotic adjustment substances of S. caninervis exhibited two types of responses. With the exception of malonyldialdehyde (MDA) and superoxide dismutase (SOD), the variables examined fitted as downward parabolic then upward parabolic temporal dynamics. The removal of shrubs is harmful to the survival of S.caninervis. In resource-constrained conditions, SOD is an important antioxidant enzyme that of peroxidase (POD), catalase (CAT) and osmotic adjustment substances, for S. caninervis survival.

Transcriptome-Wide Identification, Classification, and Characterization of AP2/ERF Family Genes in the Desert Moss Syntrichia caninervis

APETALA2/Ethylene Responsive Factor (AP2/ERF) is a large family of plant transcription factors which play important roles in the control of plant metabolism and development as well as responses to various biotic and abiotic stresses. The desert moss Syntrichia caninervis, due to its robust and comprehensive stress tolerance, is a promising organism for the identification of stress-related genes. Using S. caninervis transcriptome data, 80 AP2/ERF unigenes were identified by HMM modeling and BLASTP searching. Based on the number of AP2 domains, multiple sequence alignment, motif analysis, and gene tree construction, ScAP2/ERF genes were classified into three main subfamilies (including 5 AP2 gene members, 72 ERF gene members, and 1 RAV member) and two Soloist members. We found that the ratio for each subfamily was constant between S. caninervis and the model moss Physcomitrella patens, however, as compared to the angiosperm Arabidopsis, the percentage of ERF subfamily members in both moss species were greatly expanded, while the members of the AP2 and RAV subfamilies were reduced accordingly. The amino acid composition of the AP2 domain of ScAP2/ERFs was conserved as compared with Arabidopsis. Interestingly, most of the identified DREB genes in S. caninervis belonged to the A-5 group which play important roles in stress responses and are rarely reported in the literature. Expression profile analysis of ScDREB genes showed different gene expression patterns under dehydration and rehydration; the majority of ScDREB genes demonstrated a stronger response to dehydration relative to rehydration indicating that ScDREB may play an important role in dehydrated moss tissues. To our knowledge, this is the first study to detail the identification and characterization of the AP2/ERF gene family in a desert moss. Further, this study will lay the foundation for further functional analysis of these genes, provide greater insight to the stress tolerance mechanisms in S. caninervis and provide a reference for AP2/ERF gene family classification in other moss species.

The upside-down water collection system of Syntrichia caninervis

Desert plants possess highly evolved water conservation and transport systems, from the root structures that maximize absorption of scarce ground water(1-5), to the minimization of leaf surface area(6) to enhance water retention. Recent attention has focused on leaf structures that are adapted to collect water and promote nucleation from humid air(7-9). Syntrichia caninervis Mitt. (Pottiaceae) is one of the most abundant desert mosses in the world and thrives in an extreme environment with multiple but limited water resources (such as dew, fog, snow and rain), yet the mechanisms for water collection and transport have never been completely revealed. S. caninervis has a unique adaptation: it uses a tiny hair (awn) on the end of each leaf to collect water, in addition to that collected by the leaves themselves. Here we show that the unique multiscale structures of the hair are equipped to collect and transport water in four modes: nucleation of water droplets and films on the leaf hair from humid atmospheres; collection of fog droplets on leaf hairs; collection of splash water from raindrops; and transportation of the acquired water to the leaf itself. Fluid nucleation is accomplished in nanostructures, whereas fog droplets are gathered in areas where a high density of small barbs are present and then quickly transported to the leaf at the base of the hair. Our observations reveal nature's optimization of water collection by coupling relevant multiscale physical plant structures with multiscale sources of water.

Characterization of reference genes for RT-qPCR in the desert moss Syntrichia caninervis in response to abiotic stress and desiccation/rehydration

Syntrichia caninervis is the dominant bryophyte of the biological soil crusts found in the Gurbantunggut desert. The extreme desert environment is characterized by prolonged drought, temperature extremes, high radiation and frequent cycles of hydration and dehydration. S. caninervis is an ideal organism for the identification and characterization of genes related to abiotic stress tolerance. Reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) expression analysis is a powerful analytical technique that requires the use of stable reference genes. Using available S. caninervis transcriptome data, we selected 15 candidate reference genes and analyzed their relative expression stabilities in S. caninervis gametophores exposed to a range of abiotic stresses or a hydration-desiccation-rehydration cycle. The programs geNorm, NormFinder, and RefFinder were used to assess and rank the expression stability of the 15 candidate genes. The stability ranking results of reference genes under each specific experimental condition showed high consistency using different algorithms. For abiotic stress treatments, the combination of two genes (α-TUB2 and CDPK) were sufficient for accurate normalization. For the hydration-desiccation-rehydration process, the combination of two genes (α-TUB1 and CDPK) were sufficient for accurate normalization. 18S was among the least stable genes in all of the experimental sets and was unsuitable as reference gene in S. caninervis. This is the first systematic investigation and comparison of reference gene selection for RT-qPCR work in S. caninervis. This research will facilitate gene expression studies in S. caninervis, related moss species from the Syntrichia complex and other mosses.

Rapid adjustment of leaf angle explains how the desert moss, Syntrichia caninervis, copes with multiple resource limitations during rehydration

Although the desert moss Syntrichia caninervis Mitt. is extremely desiccation tolerant, it still requires water and photosynthates for growth. The ecological significance of the leaf angle in maintaining a balance between water and light availability is critical to its survival. Active leaf repositioning balances water and light availability following rehydration. S. caninervis can adjust leaf angles from a steep (84-69°) to a stable level at 30° within 7s after rehydration, obtaining maximum net photosynthetic gain at a shoot relative water content of ~60%. Leaf morphological characters, (leaf hair points, surface papillae and costal anatomy) and ultrastructural changes (chloroplast reordering and loss of lipid reserves as shown by changes in osmiophilic globules) were linked to rapid leaf spreading, water gain and sunlight reflectivity of leaves during rehydration. The high 377.20±91.69 (cm2g-1) surface area to mass ratio was a major factor in facilitating the rapid response to rewetting. Hyaline cells of the leaf base absorbed water, swelled and forced the leaf away from the stem as soon as rehydration commenced. Loss of leaf hair points retards leaf angle adjustment during rehydration.

The desert moss Pterygoneurum lamellatum (Pottiaceae) exhibits an inducible ecological strategy of desiccation tolerance: effects of rate of drying on shoot damage and regeneration

PREMISE OF THE STUDY

Bryophytes include clades that incorporate constitutive desiccation tolerance, especially terrestrial species. Here we test the hypothesis that the opposing ecological strategy of desiccation tolerance, inducibility, is present in a desert moss, and address this hypothesis by varying rates of drying in a laboratory study. Desiccation tolerance is arguably the most important evolutionary innovation relevant to the colonization of land by plants; increased understanding of the ecological drivers of this trait will eventually illuminate the responsible mechanisms and ultimately open doors to the potential for the application of this trait in cultivated plants.

METHODS

Plants were cloned, grown in continuous culture (dehardened) for several months, and subjected to rates of drying (drying times) ranging from 30 min to 53 h, rehydrated and tested for recovery using chlorophyll fluorescence, leaf damage, and regeneration of protonema and shoots.

KEY RESULTS

Rate of drying significantly affected all recovery responses, with very rapid drying rates severely damaging the entire shoot except the shoot apex and resulting in slower growth rates, fewer regenerative shoots produced, and a compromised photosynthetic system as inferred from fluorescence parameters.

CONCLUSIONS

For the first time, a desert moss is shown to exhibit an ecological strategy of desiccation tolerance that is inducible, challenging the assumption that arid-land bryophytes rely exclusively on constitutive protection. Results indicate that previous considerations defining a slow-dry event in bryophytes need reevaluation, and that the ecological strategy of inducible desiccation tolerance is probably more common than currently understood among terrestrial bryophytes.