Relationship between metal and pigment concentrations in the Fe-hyperaccumulator moss Scopelophila ligulata

Synergistic effects of zinc and cadmium on phytoremediation potential of Christmas moss (Vesicularia montagnei)

The hyperaccumulation potential of zinc (Zn) and cadmium (Cd) and their synergistic effects were examined in relation to Christmas moss (Vesicularia montagnei (Bél) Broth., Hypnaceae), an aquatic and terrestrial moss, dosed with Cd (Cd1 and Cd2), Zn (Zn1 and Zn2) and combined Zn and Cd (Cd1Zn1 and Cd2Zn2). Zinc promoted plant growth and development, particularly in the highest Zn and combined Zn/Cd treatments (Zn2 and Cd2Zn2). The Zn treatment resulted in substantial moss chlorophyll content and highest percentage relative growth rate in biomass value (0.23 mg L-1 and 106.8%, respectively); however, the Cd2Zn2 treatment achieved maximal production of chlorophyll a and total chlorophyll (0.29 and 0.51 mg L-1, respectively) due to synergistic effects. These findings suggest that Christmas moss is a highly metal-tolerant and adaptable bryophyte species. Zinc was essential for reducing the detrimental effects of Cd while simultaneously promoting moss growth and biomass development. Furthermore, Christmas moss exhibited hyperaccumulation potential for Cd and Zn in the Cd2Zn2 and Zn alone treatments, as evidenced by highest Cd and Zn values in gametophores (1002 and 18,596 mg per colony volume, respectively). Using energy dispersive X-ray fluorescence (EDXRF) spectrometry, atomic percentages of element concentrations in moss gametophores in the Zn2, Cd2 and combined Zn/Cd treatments were generally in the order: K > Ca > P > Zn > Cd. When comparing the atomic percentages of Zn and Cd in gametophores, it is likely that the higher atomic percentage of Zn was because this element is essential for plant growth and development.

Effects of copper accumulation on growth and development of Scopelophila cataractae grown in vitro

Scopelophila cataractae was cultured in vitro for 16 weeks to assess the contrasting effects of Cu on growth and reproduction, as well as gametophore stage. To induce buds and gametophores of S. cataractae, ten treatments (tr 1 to tr 10) of culture media were prepared using a combination of mineral salts, sugar, vitamin B complex, CuSO₄, and exogenous hormones. Highest numbers of gametophores and buds were formed in media containing 500 µM CuSO₄ in co-application with auxin and cytokinin, as shown in the modest Cu treatments (tr 6 and tr 7, 26 per cushion and 255 per 25 mm², respectively). A 5000 µM CuSO₄ concentration inhibited development of protonema, possibly due to Cu toxicity, resulting in chloronema forming contorted filaments or short cells containing lipid bodies, and brood body diaspores but no gametophore or bud formation. In this study, S. cataractae Cu accumulation in tissue was substantial (up to 2843.1 mg kg^-1; tr 6) with no or minimal adverse effects, reflecting its potential for phytoremediation of Cu in terrestrial and aquatic ecosystems. The highest atomic percentages of Cu and Zn were detected in the stem surfaces of gametophores treated with 500 µM CuSO₄ (11% atomic Cu and 7% atomic Zn), which served as a primary heavy metal storage site, ultimately protecting cells from metal toxicity. The success of this in vitro study on S. cataractae should also aid ex situ conservation efforts for a variety of rare moss taxa in the wild.

Distribution and dispersion of heavy metals in the rock-soil-moss system of the black shale areas in the southeast of Guizhou Province, China

Black shales are easily exposed due to human activities such as mining, road construction, and shale gas development, which results in several environmental issues including heavy metal (HM) pollution, soil erosion, and the destruction of vegetation. Mosses are widely used to monitor metal pollution in the atmosphere, but few studies on the distribution and dispersion of HMs in the rock-soil-moss system are available. Here, mosses (Pohlia flexuosa Harv. in Hook), growing soils, and corresponding parent rocks were collected from black shale areas. After appropriate pretreatment, samples were analyzed for multiple elemental concentrations by ICP-AES and ICP-MS. The results show that black shale parent rocks have elevated HM concentration and act as a source of multiple metals. The overlying soil significantly inherits and accumulates heavy metals released from black shale. Significant positive correlations between HMs in P. flexuosa and the growing soils indicate that HMs are mainly originating from geological source rather than atmospheric deposition. Differential accumulation of HMs is observed between rhizoids and stems in our study. Moreover, P. flexuosa is able to cope with high concentrations of toxic metals without any visible negative effect on its growth and development. Finally, the bioconcentration factor (BCF) for all the HMs in P. flexuosa is less than 1, indicating that it has a tolerance and exclusion mechanism for these metals, especially for the non-essential elements As and Pb. Therefore, the luxuriant and spontaneous growth of P. flexuosa could be used as a phytostabilization pioneer plant in the black shale outcrop where vascular plants are rare.

Is Your Moss Alive during Active Biomonitoring Study?

Biomonitoring was proposed to assess the condition of living organisms or entire ecosystems with the use of bioindicators-species sensitive to specific pollutants. It is important that the bioindicator species remains alive for as long as possible while retaining the ability to react to the negative effects of pollution (elimination/neutralization of hazardous contaminants). The purpose of the study was to assess the survival of Pleurozium schreberi moss during exposure (moss-bag technique) based on the measurement of the concentration of elements (Ni, Cu, Zn, Cd, and Pb), chlorophyll content, and its fluorescence. The study was carried out using a CCM-300 portable chlorophyll content meter, portable fluorometer, UV-Vis spectrophotometer, and a flame atomic absorption spectrometer. As a result of the laboratory tests, no significant differences were found in the chlorophyll content in the gametophytes of mosses tested immediately after collection from the forest, compared to those drying at room temperature in the laboratory (p = 0.175 for Student's t-test results). Mosses exposed using the moss-bag technique of active biomonitoring were characterized by a drop in the chlorophyll content over 12 weeks (more than 50% and 60% for chlorophyll-a and chlorophyll-b, respectively). Chlorophyll content in mosses during exposure was correlated with actual photochemical efficiency (yield) of photosystem II (calculated value of Pearson's linear correlation coefficient was 0.94-there was a significant correlation between chlorophyll a and yield p = 0.02). The highest metal increases in mosses (RAF values) were observed for zinc, lead, and copper after the second and third month of exposure. The article demonstrates that the moss exposed in an urbanized area for a period of three months maintains the properties of good bioindicator of environmental quality.

Arbuscular mycorrhizal fungi effect growth and photosynthesis of Phragmites australis (Cav.) Trin ex. Steudel under copper stress

Arbuscular mycorrhizal fungi (AMF) is an effective way to remove heavy metals' inhibition on plants, however, few relevant research attempts have been made to determine the contribution of AMF to the physiological and biochemical changes related to the enhanced copper tolerance of Phragmites australis under metal-stressed conditions. In this study, the effects of AMF inoculation on P. australis under different concentrations of copper stress were investigated according to the changes in the parameters related to growth and development, and photosynthetic charateristics. Then, differentially expressed proteins (DEPs) were evaluated by the Isobaric Tag for Relative and Absolute Quantification (iTRAQ) system, which could accurately quantify the DEPs by measuring peak intensities of reporter ions in tandem mass spectrometry (MS/MS) spectra. It was found that AMF inoculation may relieve the photosynthesis inhibition caused by copper stress on P. australis and thus promote growth. Proteomic analysis results showed that under copper stress, the inoculation of R. irregularis resulted in a total of 459 differently-expressed proteins (200 up-regulated and 259 down-regulated) in root buds. In addition, the photosynthetic changes caused by AMF inoculation mainly involve the up-regulated expression of transmembrane protein-pigment complexes CP43 (photosystem II) and FNR (ferredoxin-NADP+ oxidoreductase related to photosynthetic electron transport). These results indicate that AMF could effectively improve the growth and physiological activity of P. australis under copper stress, and thus provides a new direction and instructive evidence for determining the mechanisms by which AMF inoculation enhances the copper tolerance of plants.

A review on global metal accumulators-mechanism, enhancement, commercial application, and research trend

The biosphere is polluted with metals due to burning of fossil fuels, pesticides, fertilizers, and mining. The metals interfere with soil conservations such as contaminating aqueous waste streams and groundwater, and the evidence of this has been recorded since 1900. Heavy metals also impact human health; therefore, the emancipation of the environment from these environmental pollutants is critical. Traditionally, techniques to remove these metals include soil washing, removal, and excavation. Metal-accumulating plants could be utilized to remove these metal pollutants which would be an alternative option that would simultaneously benefit commercially and at the same time clean the environment from these pollutants. Commercial application of pollutant metals includes biofortification, phytomining, phytoremediation, and intercropping. This review discusses about the metal-accumulating plants, mechanism of metal accumulation, enhancement of metal accumulation, potential commercial applications, research trends, and research progress to enhance the metal accumulation, benefits, and limitations of metal accumulators. The review identified that the metal accumulator plants only survive in low or medium polluted environments with heavy metals. Also, more research is required about metal accumulators in terms of genetics, breeding potential, agronomics, and the disease spectrum. Moreover, metal accumulators' ability to uptake metals need to be optimized by enhancing metal transportation, transformation, tolerance to toxicity, and volatilization in the plant. This review would benefit the industries and environment management authorities as it provides up-to-date research information about the metal accumulators, limitation of the technology, and what could be done to improve the metal enhancement in the future.

Determination of iron species, including biomineralized jarosite, in the iron-hyperaccumulator moss Scopelophila ligulata by Mössbauer, X-ray diffraction, and elemental analyses

Scopelophila ligulata is an Fe-hyperaccumulator moss growing in acidic environments, but the mechanism of Fe accumulation remains unknown. To understand the mechanism, we determined Fe species in S. ligulata samples. The moss samples were collected from four sites in Japan. The concentrations of Fe, P, S, Cl, and K in them were measured by induced coupled plasma mass spectrometry. Fe species in some of them were determined by Mössbauer spectroscopy and were confirmed by X-ray diffraction analysis. Fe species in S. ligulata samples were determined to be jarosite, ferritin, high-spin Fe(II) species, and akaganeite. To our knowledge, this is the first report on the biomineralization of jarosite in mosses. This result, combined with the fact that bacteria, a fungus, and a grass mineralize jarosite, suggests that its biomineralization is a common characteristic in a wide variety of living organisms. These findings indicate that the biomineralization of jarosite occurs not only in the region-specific species but in species adapted to a low-pH and metal-contaminated environment in different regions, provide a better understanding of the mechanism of Fe accumulation in the Fe-hyperaccumulator moss S. ligulata, and offer new insights into the biomineralization of jarosite.