Metal accumulation in the acrocarp moss Atrichum undulatum under controlled conditions

Mosses are frequently used to monitor atmospheric metal contamination but few studies on metal adsorption under controlled conditions are available. Here, the accumulation of the heavy metals copper and zinc was studied in the acrocarp moss Atrichum undulatum. An in vitro culture of A. undulatum was established and the same line, size and equally old remets were exposed to six different treatments representing various metal exposure times and washing scenarios as rain simulation. The metal treatments were done in copper and zinc salts (Cu-acetate, CuSO₄, ZnSO₄ and ZnCl₂, respectively). Energy-Dispersive X-ray microanalysis (EDX) was employed to detect bound heavy metals on the moss plantlets. Element distribution in stems and leaves was measured separately. The aqueous solution of metal salts facilitated an adsorption of both elements in the moss tissue as compared to solid medium. Furthermore, A. undulatum can tolerate pollution of zinc and copper in a distinctive extent; our data point towards a higher zinc tolerance whereas copper is rather harmful. However, semi-quantitatively, less zinc was detected within the moss tissue compared to copper. Interestingly, a strong positive correlation between the accumulation of copper/zinc and iron, and a strong negative correlation between copper/zinc and magnesium, respectively, was documented.

Population dynamics of Echinops gmelinii Turcz. at different successional stages of biological soil crusts in a temperate desert in China

The effects of biological soil crusts (BSC) on vascular plant growth can be positive, neutral or negative, and little information is available on the impacts of different BSC successional stages on vascular plant population dynamics. We analysed seedling emergence, survival, plant growth and reproduction in response to different BSC successional stages (i.e. habitats: bare soil, cyanobacteria, lichen and moss crusts) in natural populations of Echinops gmelinii Turcz. in the Tengger Desert of northwest China. The winter annual E. gmelinii is a dominant pioneer herb after sand stabilisation. During the early stages of BSC succession, the studied populations of E. gmelinii were characterised by high density, plant growth and fecundity. As the BSC succession proceeded beyond moss crusts, the fecundity decreased sharply, which limited seedling recruitment. Differences in seedling survival among the successional stages were not evident, indicating that BSC have little effect on survival in arid desert regions. Moreover, E. gmelinii biomass allocation exhibited low plasticity, and only reproductive allocation was sensitive to the various habitats. Our results further suggest that the negative effects of BSC succession on population dynamics are primarily driven by increasing topsoil water-holding capacity and decreasing rain water infiltration into deeper soil. We conclude that BSC succession drives population dynamics of E. gmelinii, primarily via its effect on soil moisture. The primary cause for E. gmelinii population decline during the moss-dominated stage of BSC succession is decreased fecundity of individual plants, with declining seed mass possibly reducing the success of seedling establishment.

Moss facilitating mercury, lead and cadmium enhanced accumulation in organic soils over glacial erratic at Mt. Gongga, China

Moss is usually as an initial colonizer in alpine glacier retreated regions. We hypothesized that moss can significantly facilitate the toxic metals accumulation in alpine ecosystems based on its strong ability of absorption and the role in soil development. Hence, we investigated the trace element pool sizes and enrichment factors, especially for mercury (Hg) by using the Hg isotopic compositions to determine the source contributions in a moss-dominated ecosystem over glacial erratic in Eastern Tibetan Plateau. Results show that Hg, lead (Pb) and cadmium (Cd) are highly enriched in organic soils. Specifically, Cd concentration is 5-20 times higher than the safety limit of the acid soil (pH ≤ 5.5) in China. Atmospheric depositions dominantly contribute to the Pb and Cd sources in organic soils, and followed by the moraine particles influences. The lowering pH in organic soils increasing with glacial retreated time results in the desorption of Cd in organic soils. Atmospheric Hg⁰ uptake by moss predominantly contributes to the Hg sources in organic soils. The average Pb accumulation rate over last 125-year is about 5.6 ± 1.0 mg m^-2 yr^-1, and for Cd is 0.4 ± 0.1 mg m^-2 yr^-1, and for Hg⁰ is 27.6 ± 3.2 μg m^-2 yr^-1. These elevated accumulation rates are caused by the high moss biomass and elevated atmospheric Hg, Pb and Cd pollution levels in China and neighbouring regions. Our study indicates that the moss not only as the bioindicator, but also plays an important role in the hazardous metal biogeochemical cycling in alpine regions.

Impacts of nitrogen deposition on carbon and nitrogen cycling in alpine Racomitrium heath in the UK and prospects for recovery

Deposition of reactive nitrogen (N) is a major threat to terrestrial ecosystems associated with impacts on ecosystem properties and functions including carbon (C) and nutrient stocks, soil water quality and nutrient retention. In the oceanic-alpine Racomitrium heath habitat, N deposition is associated with moss mat degradation and a shift from bryophyte to graminoid dominance. To investigate the effects of moss mat decline on C and N stocks and fluxes, we collected Racomitrium heath vegetation/soil cores from sites along a gradient of N deposition in the UK. Cores were maintained under controlled conditions and exposed to scenarios of current (8-40 kg N ha^-1 y^-1), reduced (8 kg N ha^-1 y^-1) and elevated (50 kg N ha^-1 y^-1) N deposition. Cores from high N deposition sites had smaller aboveground C and N stocks and, under current conditions, leached large amounts of inorganic N and had low soil water pH compared with low N deposition sites. With reduced N deposition there was evidence for rapid recovery of soil water quality in terms of reduced N leaching and small increases in pH. Under high N deposition, cores from low N deposition sites retained much of the applied N while those with a history of high N deposition leached large amounts of inorganic N. Carbon fluxes in soil water and net CO₂ fluxes varied according to core source site but were not affected by the N deposition scenarios. We conclude that C and N stocks and cycling in Racomitrium heath are strongly affected by long-term exposure to N deposition but that soil water quality may improve rapidly, if N deposition rates are reduced. The legacy of N deposition impacts on moss mat cover and vegetation composition however, mean that the ecosystem remains sensitive to future pulses in N input.

Minimal auxin sensing levels in vegetative moss stem cells revealed by a ratiometric reporter

Efforts to reveal ancestral functions of auxin, a key regulator of plant growth and development, and its importance for evolution have been hampered by a fragmented picture of auxin response domains in early-diverging land plants. We report the mapping of auxin sensing and responses during vegetative moss development using novel reporters. We established a moss-specific ratiometric reporter (PpR2D2) for Auxin Response Element- and AUXIN RESPONSE FACTOR-independent auxin sensing in Physcomitrella patens, and its readout during vegetative development was compared with new promoter-based GmGH3::GFPGUS and DR5revV2::GFPGUS auxin response reporters. The ratiometric reporter responds rapidly to auxin in a time-, dose- and TRANSPORT INHIBITOR RESISTANT1/AUXIN F-BOX-dependent manner and marks known, anticipated and novel auxin sensing domains. It reveals proximal auxin sensing maxima in filamentous tissues and sensing minima in all five vegetative gametophytic stem cell types as well as dividing cells. PpR2D2 readout is compliant with an ancestral function of auxin as a positive regulator of differentiation vs proliferation in stem cell regions. The PpR2D2 reporter is a sensitive tool for high-resolution mapping of auxin sensing, which can increase our knowledge of auxin function in early-diverging land plants substantially, thereby advancing our understanding of its importance for plant evolution.

Genome-wide identification of GhAAI genes reveals that GhAAI66 triggers a phase transition to induce early flowering

Plants undergo a phase transition from vegetative to reproductive development that triggers floral induction. Genes containing an AAI (α-amylase inhibitor) domain form a large gene family, but there have been no comprehensive analyses of this gene family in any plant species. Here, we identified 336 AAI genes from nine plant species including122 AAI genes in cotton (Gossypium hirsutum). The AAI gene family has evolutionarily conserved amino acid residues throughout the plant kingdom. Phylogenetic analysis classified AAI genes into five major clades with significant polyploidization and showing effects of genome duplication. Our study identified 42 paralogous and 216 orthologous gene pairs resulting from segmental and whole-genome duplication, respectively, demonstrating significant contributions of gene duplication to expansion of the cotton AAI gene family. Further, GhAAI66 was preferentially expressed in flower tissue and as responses to phytohormone treatments. Ectopic expression of GhAAI66 in Arabidopsis and silencing in cotton revealed that GhAAI66 triggers a phase transition to induce early flowering. Further, GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis of RNA sequencing data and qRT-PCR (quantitative reverse transcription-PCR) analysis indicated that GhAAI66 integrates multiple flower signaling pathways including gibberellin, jasmonic acid, and floral integrators to trigger an early flowering cascade in Arabidopsis. Therefore, characterization of the AAI family provides invaluable insights for improving cotton breeding.

Evolution of coumaroyl conjugate 3-hydroxylases in land plants: lignin biosynthesis and defense

Multiple adaptations were necessary when plants conquered the land. Among them were soluble phenylpropanoids related to plant protection and lignin necessary for upright growth and long-distance water transport. Cytochrome P450 monooxygenase 98 (CYP98) catalyzes a rate-limiting step in phenylpropanoid biosynthesis. Phylogenetic reconstructions suggest that a single copy of CYP98 founded each major land plant lineage (bryophytes, lycophytes, monilophytes, gymnosperms and angiosperms), and was maintained as a single copy in all lineages but the angiosperms. In angiosperms, a series of independent gene duplications and losses occurred. Biochemical assays in four angiosperm species tested showed that 4-coumaroyl-shikimate, a known intermediate in lignin biosynthesis, was the preferred substrate of one member in each species, while independent duplicates in Populus trichocarpa and Amborella trichopoda each showed broad substrate ranges, accepting numerous 4-coumaroyl-esters and -amines, and were thus capable of producing a wide range of hydroxycinnamoyl conjugates. The gymnosperm CYP98 from Pinus taeda showed a broad substrate range, but preferred 4-coumaroyl-shikimate as its best substrate. In contrast, CYP98s from the lycophyte Selaginella moellendorffii and the fern Pteris vittata converted 4-coumaroyl-shikimate poorly in vitro, but were able to use alternative substrates, in particular 4-coumaroyl-anthranilate. Thus, caffeoyl-shikimate appears unlikely to be an intermediate in monolignol biosynthesis in non-seed vascular plants, including ferns. The best substrate for CYP98A34 from the moss Physcomitrella patens was also 4-coumaroyl-anthranilate, while 4-coumaroyl-shikimate was converted to lower extents. Despite having in vitro activity with 4-coumaroyl-shikimate, CYP98A34 was unable to complement the Arabidopsis thaliana cyp98a3 loss-of-function phenotype, suggesting distinct properties also in vivo.

Giberellic Acid-Stimulated Transcript Proteins Evolved through Successive Conjugation of Novel Motifs and Their Subfunctionalization

Gibberellic Acid Stimulated Transcript (GAST)-like genes encode small polypeptides, some of which have been implicated in diverse biological processes regulating plant growth and development. However, the occurrence of GASTs among plants, their protein structures, and the mechanisms by which they evolved remain elusive. Here, using a customized workflow, we report genes encoding GAST proteins, identify novel motifs and evolutionary patterns contributing to the subfunctionalization of GAST domains, and explore functional conservation across diverse plant groups. We show that GAST-like sequences evolved initially in the vascular plant Selaginella moellendorffii, after the divergence from bryophytes, and later emerged in gymnosperms and angiosperms. GASTs in angiosperms are characterized by four conserved novel motifs; however, relatively fewer conserved motifs exist in pteridophytes and gymnosperms. Phylogenetic analysis revealed that the GAST-Cysteine Rich1 motif evolved early in the S. moellendorffii GAST, which further acquired subfunctionalization through successive conjugation of other motifs and remained conserved across plants, as supported by their collinearity. Functional characterization of two orthologs from the dicot Arabidopsis (Arabidopsis thaliana; Gibberellic Acid-Stimulated Arabidopsis 10) and the monocot rice (Oryza sativa; Gibberellic Acid Stimulated Transcript-Related 9) suggests hormonal regulation, novel roles in seed germination, and functional conservation among diverse plant groups. Computational modeling predicts that these GAST genes are regulated by several factors, including the phytohormones gibberellin and abscisic acid, through conserved cis-motifs present in their promoters, and that they might act as signaling molecules in a complex feedback loop. Thus, our study identifies GASTs and their encoded proteins, uncovers their structure, novel motifs, and evolutionary pattern among plants, and suggests their functional conservation.

Mercury isotopic compositions of mosses, conifer needles, and surface soils: Implications for mercury distribution and sources in Shergyla Mountain, Tibetan Plateau

Understanding the distribution and sources of mercury (Hg) in the Tibetan Plateau is of great value to study the long-range transport of Hg. Herein, the total Hg (THg) concentrations and the isotopic compositions of mosses, conifer needles, and surface soils collected from both slopes of the Shergyla Mountain of Tibetan Plateau were analyzed. The contents of THg in samples (except mosses on the eastern slope) were significantly positively correlated with altitude in both the western and eastern slopes, possibly caused by topographic factors. In contrast, Δ¹⁹⁹Hg in samples was significantly negatively correlated with altitude. On the basis of Hg isotopic compositions, atmospheric Hg⁰ uptake was indicated as the primary accumulation pathway of Hg in mosses (Δ¹⁹⁹Hg: -0.12 ± 0.09‰, -0.26 - 0.00‰, 1 SD, n = 10) and conifer needles (Δ¹⁹⁹Hg: -0.21 ± 0.08‰, -0.36 - -0.11‰, 1 SD, n = 9). Moreover, the contributing fractions of atmospheric Hg⁰ to Hg in surface soils (Δ¹⁹⁹Hg: -0.20 ± 0.07‰, -0.31 - -0.06‰, 1 SD, n = 17) increased with altitude and accounted for an average of 87 ± 9% in atmospheric sources. Due to the special geographic positions and environmental conditions of the Tibetan Plateau, the results of this study were essential for further understanding the long-range transport and global cycling of Hg.

Nuclear protein phylogenies support the monophyly of the three bryophyte groups (Bryophyta Schimp.)

Unraveling the phylogenetic relationships between the four major lineages of terrestrial plants (mosses, liverworts, hornworts, and vascular plants) is essential for an understanding of the evolution of traits specific to land plants, such as their complex life cycles, and the evolutionary development of stomata and vascular tissue. Well supported phylogenetic hypotheses resulting from different data and methods are often incongruent due to processes of nucleotide evolution that are difficult to model, for example substitutional saturation and composition heterogeneity. We reanalysed a large published dataset of nuclear data and modelled these processes using degenerate-codon recoding and tree-heterogeneous composition substitution models. Our analyses resolved bryophytes as a monophyletic group and showed that the nonnonmonophyly of the clade that is supported by the analysis of nuclear nucleotide data is due solely to fast-evolving synonymous substitutions. The current congruence among phylogenies of both nuclear and chloroplast analyses lent considerable support to the conclusion that the bryophytes are a monophyletic group. An initial split between bryophytes and vascular plants implies that the bryophyte life cycle (with a dominant gametophyte nurturing an unbranched sporophyte) may not be ancestral to all land plants and that stomata are likely to be a symplesiomorphy among embryophytes.

N2 fixation associated with the bryophyte layer is suppressed by low levels of nitrogen deposition in boreal forests

Biological fixation of atmospheric nitrogen (N₂) by bryophyte-associated cyanobacteria is an important source of plant-available N in the boreal biome. Information on the factors that drive biological N₂ fixation (BNF) rates is needed in order to understand the N dynamics of forests under a changing climate. We assessed the potential of several cryptogam species (the feather mosses Hylocomium splendens and Pleurozium schreberi, a group of Dicranum bryophytes, two liverworts, and Cladina lichens) to serve as associates of cyanobacteria or other N₂-fixing bacteria (diazotrophs) using acetylene reduction assay (ARA). We tested the hypotheses that the legacy of chronic atmospheric N deposition reduces BNF in the three bryophyte species, sampled from 12 coniferous forests located at latitudes 60-68° N in Finland. In addition, we tested the effect of moisture and temperature on BNF. All species studied showed a BNF signal in the north, with the highest rates in feather mosses. In moss samples taken along the north-south gradient with an increasing N bulk deposition from 0.8 to 4.4 kg ha^-1 year^-1, we found a clear decrease in BNF in both feather mosses and Dicranum group. BNF turned off at N deposition of 3-4 kg ha^-1 year^-1. Inorganic N (NH₄-N + NO₃-N) best predicted the BNF rate among regression models with different forms of N deposition as explanatory variables. However, in southern spruce stands, tree canopies modified the N in throughfall so that dissolved organic N (DON) leached from canopies compensated for inorganic N retained therein. Here, both DON and inorganic N negatively affected BNF in H. splendens. In laboratory experiments, BNF increased with increasing temperature and moisture. Our results suggest that even relatively low N deposition suppresses BNF in bryophyte-associated diazotrophs. Further, BNF could increase in northern low-deposition areas, especially if climate warming leads to moister conditions, as predicted.

Multi-element composition of soil, mosses and mushrooms and assessment of natural and artificial radioactivity of a pristine temperate rainforest system (Slavonia, Croatia)

This study investigates multi-element composition of soil, mosses and mushrooms from a pristine temperate rainforest (Prašnik, Croatia). Additionally, the activity levels of natural (²³⁸U, ²³⁵U and ²³²Th decay chains, ⁴⁰K and ⁷Be) and anthropogenic (¹³⁷Cs and ¹³⁴Cs) radionuclides in the investigated soil samples, obtained by gamma spectrometry, provide baseline of environmental radioactivity levels in this area. The aim of investigation was to explore the uptake of metal(loid)s by bioindicator species (mosses, mushrooms) growing in a pristine environment characterized by naturally elevated concentration of metals. The calculated enrichment and bioaccumulation factors, correlations between different groups of elements and similar multi-element patterns in mosses, mushrooms and soil samples revealed the prevailing influence of the local substrate geochemistry on element concentrations in mosses and mushrooms. The results suggest atmospheric deposition of Bi, Cd and Pb, while radionuclide activities point to atmospheric fall-out (including global contamination by radiocaesium) and influence of the pedological substrate. The confined area of investigation, with limited variations in soil characteristics and geological composition, allowed clearer insight into the origin of metal(loid)s in mosses and mushrooms. On the other hand, using bioindicator species with different element uptake mechanisms enabled distinction between different sources of elements.

Phenolic compounds from different bryophyte species and cell compartments respond specifically to ultraviolet radiation, but not particularly quickly

To study the potential quick responses to ultraviolet (UV) radiation of bryophyte phenolic compounds, we cultivated two thalloid liverworts, two leafy liverworts, and two mosses under three moderate realistic UV levels in the laboratory for 22 days. At the end of the daylight period on the first and last culture days, we measured the bulk levels and individual contents of phenolic UV-absorbing compounds (UVACs) of each species, differentiating in both cases the UVACs located in the methanol-soluble (mainly vacuolar) and -insoluble (cell wall-bound) fractions (SUVACs and IUVACs, respectively). The bulk levels of SUVACs and IUVACs mostly showed linear or hyperbolic relationships with the UV dose applied. Thirteen flavones (apigenin and luteolin derivatives) and two hydroxycinnamic acids (p-coumaric and ferulic acids) were identified in the soluble and insoluble fractions, respectively. Only two compounds (p-coumaric and ferulic acids) from the insoluble fraction of the leafy liverwort Plagiochila asplenioides showed a significant quick accumulation in response to UV radiation in the first day of culture, whereas six UVACs (mainly soluble apigenin and luteolin derivatives) from different species (mainly liverworts) were significantly accumulated at the end of the culture. In conclusion, the responses of bryophyte UVACs to UV radiation were influenced by the specific compound considered, the fraction in which each UVAC was located, the global or individual way of UVACs quantification, the bryophyte species and evolutionary lineage, and the experimental conditions used. Particularly, SUVACs were more UV-responsive than IUVACs and liverworts than mosses, and responses were not especially quick.

Photoprotection enhanced by red cell wall pigments in three East Antarctic mosses

BACKGROUND

Antarctic bryophytes (mosses and liverworts) are resilient to physiologically extreme environmental conditions including elevated levels of ultraviolet (UV) radiation due to depletion of stratospheric ozone. Many Antarctic bryophytes synthesise UV-B-absorbing compounds (UVAC) that are localised in their cells and cell walls, a location that is rarely investigated for UVAC in plants. This study compares the concentrations and localisation of intracellular and cell wall UVAC in Antarctic Ceratodon purpureus, Bryum pseudotriquetrum and Schistidium antarctici from the Windmill Islands, East Antarctica.

RESULTS

Multiple stresses, including desiccation and naturally high UV and visible light, seemed to enhance the incorporation of total UVAC including red pigments in the cell walls of all three Antarctic species analysed. The red growth form of C. purpureus had significantly higher levels of cell wall bound and lower intracellular UVAC concentrations than its nearby green form. Microscopic and spectroscopic analyses showed that the red colouration in this species was associated with the cell wall and that these red cell walls contained less pectin and phenolic esters than the green form. All three moss species showed a natural increase in cell wall UVAC content during the growing season and a decline in these compounds in new tissue grown under less stressful conditions in the laboratory.

CONCLUSIONS

UVAC and red pigments are tightly bound to the cell wall and likely have a long-term protective role in Antarctic bryophytes. Although the identity of these red pigments remains unknown, our study demonstrates the importance of investigating cell wall UVAC in plants and contributes to our current understanding of UV-protective strategies employed by particular Antarctic bryophytes. Studies such as these provide clues to how these plants survive in such extreme habitats and are helpful in predicting future survival of the species studied.

Abscisic acid, cold and salt stimulate conserved metabolic regulation in the moss Physcomitrella patens

Salt and cold are major abiotic stresses that have adverse effects on plant growth and development. To cope with these stresses and their detrimental effects plants have evolved several metabolic, biochemical and physiological processes that are mainly triggered and mediated by the plant hormone abscisic acid (ABA). To elucidate the metabolic responses of the moss Physcomitrella patens, which serves as a model plant for abiotic stress adaptation, we performed GC-MS-based metabolic profiling of plants challenged for 5 and 28 h with either salt, cold or ABA. Our results indicate significant changes in the accumulation of several sugars including maltose, isomaltose and trehalose, amino acids including arginine, histidine, ornithine, tryptophan and tyrosine, and organic acids mainly citric acid and malonic acid. The metabolic responses provoked by ABA, cold and salt show considerable similarities. The accumulation of certain metabolites positively correlates with gene expression data whereas some metabolites do not show correlation with cognate transcript abundance. To place our results into an evolutionary context we compared the ABA- and stress-induced metabolic changes in moss to available metabolic profiles of the seed plant Arabidopsis thaliana. We detected considerable conservation between the species, indicating early evolution of stress-associated metabolic adaptations that probably occurred at the plant water-to-land transition.

Characterization of nitrogen deposition in a megalopolis by means of atmospheric biomonitors

An increase of nitrogen deposition resulting from human activities is not only a major threat for global biodiversity, but also for human health, especially in highly populated regions. It is thus important and in some instances legally mandated to monitor reactive nitrogen species in the atmosphere. The utilization of widely distributed biological species suitable for biomonitoring may be a good alternative. We assessed the suitability of an ensemble of atmospheric biomonitors of nitrogen deposition by means of an extensive sampling of a lichen, two mosses, and a bromeliad throughout the Valley of Mexico, whose population reaches 30 million, and subsequent measurements of nitrogen metabolism parameters. In all cases we found significant responses of nitrogen content, C:N ratio and the δ15N to season and site. In turn, the δ15N for the mosses responded linearly to the wet deposition. Also, the nitrogen content (R2 = 0.7), the C:N ratio (R2 = 0.6), and δ15N (R2 = 0.5) for the bromeliad had a linear response to NOx. However, the bromeliad was not found in sites with NOx concentrations exceeding 80 ppb, apparently of as a consequence of excess nitrogen. These biomonitors can be utilized in tandem to determine the status of atmospheric nitrogenous pollution in regions without monitoring networks for avoiding health problems for ecosystems and humans.

Canopy structure affects temperature distributions and free convection in moss shoot systems

PREMISE OF THE STUDY

Nonvascular plants play important roles in exchange of water and heat at the soil-atmosphere interface. Differential evaporative cooling may cause temperature gradients within bryophyte canopies, influencing convective heat and mass transport. Understanding mechanisms that affect fluxes through moss layers should improve models of forest floor function.

METHODS

A three-dimensional thermal imaging system measured temperature distributions within moss shoot systems that were used to explore relationships among canopy structure, temperature gradients, evaporation, and conductance to water vapor (g_s ). We studied five moss species under dark and light conditions in the lab. Also, these properties were measured in two species that differed in canopy structure during drying.

KEY RESULTS

Differential evaporative cooling led to a 1.4 to 5.0°C range in shoot temperatures within canopies. Samples displayed -0.5 to -0.9°C/cm temperature gradients with cooler apical temperatures. Gradient magnitudes did not differ among species, but taller canopies expressed greater temperature differences. Light enhanced both the gradient and the temperature difference. Rates of evaporation were significantly related to canopy height in the light, but not in the dark, although g_s was positively associated with canopy height in both. Rayleigh (Ra) numbers characterize whether temperature gradients likely generate free convection. In tall canopies, Ra numbers exceeded the value indicative of free convection and turbulent flow. As plants dried, temperature gradients decreased.

CONCLUSIONS

When moss canopies are wet, cooler apical temperatures create thermal instabilities within the canopies that appear sufficient to enhance convective transport of water vapor and heat in tall canopies with low bulk density.

Computational workflow to study the seasonal variation of secondary metabolites in nine different bryophytes

In Eco-Metabolomics interactions are studied of non-model organisms in their natural environment and relations are made between biochemistry and ecological function. Current challenges when processing such metabolomics data involve complex experiment designs which are often carried out in large field campaigns involving multiple study factors, peak detection parameter settings, the high variation of metabolite profiles and the analysis of non-model species with scarcely characterised metabolomes. Here, we present a dataset generated from 108 samples of nine bryophyte species obtained in four seasons using an untargeted liquid chromatography coupled with mass spectrometry acquisition method (LC/MS). Using this dataset we address the current challenges when processing Eco-Metabolomics data. Here, we also present a reproducible and reusable computational workflow implemented in Galaxy focusing on standard formats, data import, technical validation, feature detection, diversity analysis and multivariate statistics. We expect that the representative dataset and the reusable processing pipeline will facilitate future studies in the research field of Eco-Metabolomics.

Phytofiltration of arsenic by aquatic moss (Warnstorfia fluitans)

This work investigates whether aquatic moss (Warnstorfia fluitans) originating from an arsenic (As)-contaminated wetland close to a mine tailings impoundment may be used for phytofiltration of As. The aim was to elucidate the capacity of W. fluitans to remove As from arsenite and arsenate contaminated water, how nutrients affect the As uptake and the proportion of As adsorption and absorption by the moss plant, which consists of dead and living parts. Arsenic removal from 0, 1, or 10% Hoagland nutrient solution containing 0-100 μM arsenate was followed over 192 h, and the total As in aquatic moss after treatment was analysed. The uptake and speciation of As in moss cultivated in water containing 10 μM arsenate or arsenite were examined as As uptake in living (absorption + adsorption) and dead (adsorption) plant parts. Results indicated that W. fluitans removed up to 82% of As from the water within one hour when 1 μM arsenate was added in the absence of nutrients. The removal time increased with greater nutrient and As concentrations. Up to 100 μM As had no toxic effect on the plant biomass. Both arsenite and arsenate were removed from the solution to similar extents and, independent of the As species added, more arsenate than arsenite was found in the plant. Of the As taken up, over 90% was firmly bound to the tissue, a possible mechanism for resisting high As concentrations. Arsenic was both absorbed and adsorbed by the moss, and twice as much As was found in living parts as in dead moss tissue. This study revealed that W. fluitans has potential to serve as a phytofilter for removing As from As-contaminated water without displaying any toxic effects of the metalloid.

Vascular plant and bryophyte species richness in response to water quality in lowland spring niches with different anthropogenic impacts

Many freshwater ecosystems face severe threats from anthropogenic disturbances. In the field, we investigated the morphology of spring niches and the species richness of vascular plants and bryophytes in 16 springs, draining the quaternary aquifers, located in two different environments-an urban area (city of Białystok) and a protected area (Knyszyn Forest Landscape Park, NE Poland). In total, 47 vascular plant and 45 bryophyte species were recorded, representing mostly crenophytes including protected species. The most important water quality parameters that can be used to evaluate variations of the spring water chemistry in NE Poland are the mineral-related parameters (electrolytic conductivity, Ca2+, SO42-, and Cl-). The organic-related parameters (DOC) and nutrients (TP, NO3--N) were negatively involved in water quality variations. Our results show that anthropogenic activity significantly affects the biodiversity of plant communities in lowland springs. The presence or absence of crenophytes and bryophytes is indicative of the ecological status of the groundwater outflow complexes.

Diel hysteresis between soil respiration and soil temperature in a biological soil crust covered desert ecosystem

Soil respiration induced by biological soil crusts (BSCs) is an important process in the carbon (C) cycle in arid and semi-arid ecosystems, where vascular plants are restricted by the harsh environment, particularly the limited soil moisture. However, the interaction between temperature and soil respiration remains uncertain because of the number of factors that control soil respiration, including temperature and soil moisture, especially in BSC-dominated areas. In this study, the soil respiration in moss-dominated crusts and lichen-dominated crusts was continuously measured using an automated soil respiration system over a one-year period from November 2015 to October 2016 in the Shapotou region of the Tengger Desert, northern China. The results indicated that over daily cycles, the half-hourly soil respiration rates in both types of BSC-covered areas were commonly related to the soil temperature. The observed diel hysteresis between the half-hourly soil respiration rates and soil temperature in the BSC-covered areas was limited by nonlinearity loops with semielliptical shapes, and soil temperature often peaked later than the half-hourly soil respiration rates in the BSC-covered areas. The average lag times between the half-hourly soil respiration rates and soil temperature for both types of BSC-covered areas were two hours over the diel cycles, and they were negatively and linearly related to the volumetric soil water content. Our results highlight the diel hysteresis phenomenon that occurs between soil respiration rates and soil temperatures in BSC-covered areas and the negative response of this phenomenon to soil moisture, which may influence total C budget evaluations. Therefore, the interactive effects of soil temperature and moisture on soil respiration in BSC-covered areas should be considered in global carbon cycle models of desert ecosystems.

Nitrogen deposition drives loss of moss cover in alpine moss-sedge heath via lowered C : N ratio and accelerated decomposition

In alpine ecosystems, nitrogen (N) deposition has been linked to plant community composition change, including loss of bryophytes and increase of graminoids. Since bryophyte growth is stimulated by increased N availability, it has been hypothesized that loss of bryophyte cover is driven by enhanced decomposition. As bryophyte mats are a significant carbon (C) store, their loss may impact C storage in these ecosystems. We used an N deposition gradient across 15 sites in the UK to examine effects of N deposition on bryophyte litter quality, decomposition and C and N stocks in Racomitrium moss-sedge heath. Increasing N deposition reduced C : N in bryophyte litter, which in turn enhanced decomposition. Soil N stocks increased significantly in response to increased N deposition, and soil C : N declined. However, depletion of the bryophyte mat and its replacement by graminoids under high N deposition was not associated with a change in total ecosystem C stocks. We conclude that decomposition processes in Racomitrium heath are very sensitive to N deposition and provide a mechanism by which N deposition drives depletion of the bryophyte mat. Nitrogen deposition did not measurably alter C stocks, but changes in soil N stocks and C : N suggest the ecosystem is becoming N saturated.

Biomonitoring chromium III or VI soluble pollution by moss chlorophyll fluorescence

We systematically compared the impacts of four Cr salts (chromic chloride, chromic nitrate, potassium chromate and potassium bichromate) on physiological parameters and chlorophyll fluorescence in indigenous moss Taxiphyllum taxirameum. Among the four Cr salts, K₂Cr₂O₇ treatment resulted in the most significant decrease in photosynthetic efficiency and antioxidant enzymes, increase in reactive oxygen species (ROS), and obvious cell death. Different form the higher plants, although hexavalent Cr(VI) salt treatments resulted in higher accumulation levels of Cr and were more toxic than Cr(III) salts, Cr(III) also induced significant changes in moss physiological parameters and chlorophyll fluorescence. Our results showed that Cr(III) and Cr(VI) could be monitored distinguishably according to the non-photochemical quenching (NPQ) fluorescence of sporadic purple and sporadic lavender images respectively. Then, the valence states and concentrations of Cr contaminations could be evaluated according to the image of maximum efficiency of PSII photochemistry (Fv/Fm) and the quantum yield of PSII electron transport (ΦPSII). Therefore, this study provides new ideas of moss's sensibility to Cr(III) and a new method to monitor Chromium contaminations rapidly and non-invasively in water.

Metal(loid) accumulation in aquatic plants of a mining area: Potential for water quality biomonitoring and biogeochemical prospecting

Aquatic bryophytes can accumulate extremely high levels of chemical elements because of their unique morphology and physiology which is markedly different from vascular plants. Four aquatic mosses-Fontinalis squamosa, Brachythecium rivulare, Platyhypnidium riparioides, Thamnobryum alopecurum-and a freshwater red alga Lemanea fluviatilis along with water samples from the streams of Góis mine region in Central Portugal were analyzed for 46 elements. Despite being below detection levels in the water samples, the elements Zr, V, Cr, Mo, Ru, Os, Rh, Ir, Pt, Ag, Ge and Bi were obtained in the plant samples. The moss T. alopecurum had the highest mean concentrations of 19 elements followed by B. rivulare (15 elements). Maximum accumulation of Rb, Ta and Au, however, was seen in the alga L. fluviatilis. Bioconcentration factors > 10⁶ were obtained for a few metals. The investigation confirms that aquatic bryophytes can be suitable for water quality biomonitoring and biogeochemical prospecting in fresh water bodies owing to their high accumulative capacity of multi-elements from their aquatic ambient.

Is the Binding Pattern of Zinc(II) Equal in Different Bryophyte Species?

Bryophytes are usually taken as good bioindicators. However, they represent a large group of terrestrial plants and they express an enormous range of peculiarities within the plant kingdom. With the aim to search for a common pattern of zinc binding, we established axenical in vitro cultures of a dozen bryophyte species that include hornworts, thallose, and leafy liverworts, as well as acrocarp and pleurocarp mosses. The species were grown free of contaminants for many years prior to the application of different treatments, i.e. offering Zn(II) from solid and liquid media and in combination with different anions. The localization and binding of zinc was detected by confocal microscopy using the zinc-specific dye FluoZin™-3. In one of the species, Hypnum cupressiforme (which is widely used for atmospheric heavy metal deposition studies in biomonitoring), semi-quantitative analyses of zinc were performed by energy dispersive X-ray microspectrometry (EDX) in a scanning electron microscope. The results suggest no common pattern of Zn(II) binding in different bryophyte species. Instead, the binding pattern seems to be species specific. Zinc is located in certain areas or cellular compartments, as clearly shown by the EDX measurements in H. cupressiforme.