Characteristics of endophytic fungi from Polygonum hydropiper suggest potential application for P-phytoextraction

Effect of various phosphorus levels on the extraction of Cd, the transformation of P, and phosphorus-related gene during the phytoremediation of Cd contaminated soil

Phytoremediation has emerged as a common technique for remediating Cd pollution in farmland soil. Moreover, phosphorus, an essential element for plants, can alter the pectin content of plant cell walls and facilitate the accumulation of Cd in plant tissues, thereby enhancing phytoremediation efficiency. Therefore, pot experiments were conducted in order to investigate the effect of phosphorus levels on Cd extraction, phosphorus transformation and phosphorus-related genes during phytoremediation. The results revealed that an optimal application of suitable phosphate fertilizers elevated the soil's pH and electrical conductivity (EC), facilitated the conversion of soil from insoluble phosphorus into available forms, augmented the release of pertinent enzyme activity, and induced the expression of phosphorus cycling-related genes. These enhancements in soil conditions significantly promoted the growth of ryegrass. When applying phosphorus at a rate of 600 mg/kg, ryegrass exhibited plant height, dry weight, and chlorophyll relative content that were 1.27, 1.26, and 1.18 times higher than those in the control group (P0), while the Cd content was 1.12 times greater than that of P0. The potentially toxic elements decline ratio and bioconcentration factor were 42.86% and 1.17 times higher than those of P0, respectively. Consequently, ryegrass demonstrated the highest Cd removal efficiency under these conditions. Results from redundancy analysis (RDA) revealed a significant correlation among pH, total phosphorus, heavy metal content, phosphorus forms, soil enzyme activity, and phosphorus-related genes. In conclusion, this study suggests applying an optimal amount of suitable phosphate fertilizers can enhance restoration efficiency, leading to a reduction in soil Cd content and ultimately improving the safety of crop production in farmlands.

Recycling eutrophic lake sediments into grass production: A four-year field experiment on agronomical and environmental implications

Inefficient use of phosphorus (P) fertilizers leads to the transfer of P into water bodies, causing their eutrophication. Sediment removal is a promising lake restoration strategy that removes nutrients including P accumulated in lake sediments, and opens the opportunity to use removed nutrients in agriculture. In the present study, we investigated the effects of using a thick layer of sediment from the eutrophic Lake Mustijärv on plant growth, and estimated the environmental impacts of different sediment application methods by analyzing greenhouse gas emissions, N and P leaching, aggregate stability, and soil biota. The field experiment (2017-2020) was established on the lake shore with the following treatments: the agricultural control soil (Soil) surrounding the lake, pure sediment (Sed), biochar-treated sediment (SB), and biochar and soil mixed with sediment (SSB). The sediment-based treatments resulted in a similar grass growth performance to the Soil. The availability of most macro- and micronutrients including P (75 vs. 21 g m^-3) were far greater in the Sed compared to the Soil. The sediment-based growing media emitted more CO₂ than the Soil (579 vs. 400 mg CO₂ - C m^-2 h^-1) presumably due to the high rate of organic matter decomposition. The bacterial and fungal community structures of the Sed were strongly differentiated from those of Soil. Also, Sed had lower bacterial diversity and a higher abundance of the bacterial phyla associated with solubilizing P including Proteobacteria and Chloroflexi. Sediment-based growing media increased more than seven times the risk of mineral N and P leaching, and the biochar treatment only had a short-lived beneficial effect on reduction of the sediment's leached P concentration. The sediment application rate should be adjusted to match the crop requirements to minimize greenhouse gas emissions and nutrient leaching when upscaling the case study to larger lakes with similar sediment properties.

Endophytic Fungal Community of Stellera chamaejasme L. and Its Possible Role in Improving Host Plants' Ecological Flexibility in Degraded Grasslands

Stellera chamaejasme L. is a widely distributed poisonous plant in Chinese degraded grasslands. To investigate the role of endophytic fungi (EF) in S. chamaejasme's quick spread in grasslands, the endophytic fungal community of S. chamaejasme was studied through culture-dependent and culture-independent methods, and the plant-growth-promoting (PGP) traits of some culturable isolates were tested. Further, the growth-promoting effects of 8 isolates which showed better PGP traits were evaluated by pot experiments. The results showed that a total of 546 culturable EF were isolated from 1114 plant tissue segments, and the colonization rate (CR) of EF in roots (33.27%) was significantly higher than that in shoots (22.39%). Consistent with this, the number of specific types of EF was greater in roots (8 genera) than in shoots (1 genus). The same phenomenon was found in culture-independent study. There were 95 specific genera found in roots, while only 18 specific genera were found in shoots. In addition, the dominant EF were different between the two study methods. Cladosporium (18.13%) and Penicillium (15.93%) were the dominant EF in culture-dependent study, while Apiotrichum (13.21%) and Athelopsis (5.62%) were the dominant EF in culture-independent study. PGP trait tests indicated that 91.30% of the tested isolates (69) showed phosphorus solubilization, IAA production, or siderophores production activity. The benefit of 8 isolates on host plants' growth was further studied by pot experiments, and the results indicated that all of the isolates can improve host plants' growth. Among them, STL3G74 (Aspergillus niger) showed the best growth-promotion effect; it can increase the plant's shoot and root dry biomass by 68.44% and 74.50%, respectively, when compared with the controls. Our findings revealed that S. chamaejasme has a wide range of fungal endophytic assemblages, and most of them possess PGP activities, which may play a key role in its quick spread in degraded grasslands.

Sustainable Applications of Endophytic Bacteria and Their Physiological/Biochemical Roles on Medicinal and Herbal Plants: Review

Bacterial endophytes reside within the tissues of living plant species without causing any harm or disease to their hosts. These endophytes can be isolated, identified, characterized, and used as biofertilizers. Moreover, bacterial endophytes increase the plants' resistance against diseases, pests, and parasites, and are a promising source of pharmaceutically important bioactives. For instance, the production of antibiotics, auxins, biosurfactants, cytokinin's, ethylene, enzymes, gibberellins, nitric oxide organic acids, osmolytes, and siderophores is accredited to the existence of various bacterial strains. Thus, this manuscript intends to review the sustainable applications of endophytic bacteria to promote the growth, development, and chemical integrity of medicinal and herbal plants, as well as their role in plant physiology. The study of the importance of bacterial endophytes in the suppression of diseases in medicinal and herbal plants is crucial and a promising area of future investigation.

The dynamics of phosphorus fractions and the factors driving phosphorus cycle in Zoige Plateau peatland soil

Phosphorus (P) is an essential nutrient, limiting plant growth and microbial activity in many ecosystems. However, a few studies have been conducted to investigate P dynamics and the factors driving P dynamics in peatland soils. Therefore, this study chose Zoige Plateau peatland (the largest peatland in China) to reveal P dynamics and the possible driving factors through fractionating soil P and investigating a series of abiotic and biotic factors. It is found that season, peatland type, and soil depth could strongly affect P dynamics. H₂O-P and NaHCO₃-P (labile P) had lower content, while NaOH-P, HCl-P, Mix-P, and Residual-P (non-labile P) were the dominant fractions. Besides, the sum of P fractions was higher than the traditional measurement of total P, suggesting P storage might be underestimated in peatland soils. Moreover, it is observed that biotic factors affected P fractions more than abiotic factors, and fungi affected refractory P more than bacteria. This study provides essential information for understanding P cycling in peatland soils and emphasizes specific microbes related to P cycling, which should be paid more attention to in the future.

Arnebia euchroma, a Plant Species of Cold Desert in the Himalayas, Harbors Beneficial Cultivable Endophytes in Roots and Leaves

The endophytic mutualism of plants with microorganisms often leads to several benefits to its host including plant health and survival under extreme environments. Arnebia euchroma is an endangered medicinal plant that grows naturally in extreme cold and arid environments in the Himalayas. The present study was conducted to decipher the cultivable endophytic diversity associated with the leaf and root tissues of A. euchroma. A total of 60 bacteria and 33 fungi including nine yeasts were isolated and characterized at the molecular level. Among these, Proteobacteria was the most abundant bacterial phylum with the abundance of Gammaproteobacteria (76.67%) and genus Pseudomonas. Ascomycota was the most abundant phylum (72.73%) dominated by class Eurotiales (42.42%) and genus Penicillium among isolated fungal endophytes. Leaf tissues showed a higher richness (S_chao1) of both bacterial and fungal communities as compared to root tissues. The abilities of endophytes to display plant growth promotion (PGP) through phosphorus (P) and potassium (K) solubilization and production of ACC deaminase (ACCD), indole acetic acid (IAA), and siderophores were also investigated under in vitro conditions. Of all the endophytes, 21.51% produced ACCD, 89.25% solubilized P, 43.01% solubilized K, 68.82% produced IAA, and 76.34% produced siderophores. Six bacteria and one fungal endophyte displayed all the five PGP traits. The study demonstrated that A. euchroma is a promising source of beneficial endophytes with multiple growth-promoting traits. These endophytes can be used for improving stress tolerance in plants under nutrient-deficient and cold/arid conditions.

Characterization of siderophore-producing microorganisms associated to plants from high-Andean heavy metal polluted soil from Callejón de Huaylas (Ancash, Perú)

Endophytic and rhizospheric microorganisms associated with six native plants adapted to heavy metal polluted soil from Punta Olímpica and Chahuapampa, located in Callejón de Huaylas mountains, were evaluated as potential candidates for technologies to clean polluted ecosystems. It was selected 14 bacteria and 9 fungi strains by their iron and/or aluminum siderophore production trait, where BEP17-Dm showed higher production. According to the 16S rDNA analysis, bacteria belong to Pseudomonas, Bacillus, and Achromobacter genera, whereas by ITS analysis fungi belong to Talaromyces, Hypoxylon, Tolypocladium, and Penicillium. All bacteria strains tolerated lead (2-8 mM) and eigth tolerated cadmium (1-6 mM); also all fungi tolerated lead (9-70 mM) and cadmium (3-10 mM). Two bacteria and six fungi solubilized cadmium carbonate, while eleven bacteria and two fungi solubilized tricalcium phosphate, where P. japonica BEP18-Dm and B. subtilis BRU16-Sr exhibited higher solubilization index. None strains solubilized lead carbonate. BEP18-Dm produced higher concentration of IAA (53.42 μgml^-1); while six bacteria and all fungi strains produced a low concentration of auxins. Medicago sativa seedlings inoculated with BEP17-Dm, BEP18-Dm, or BRU16-Sr showed more surviving percentage under in vitro culture in presence of Cd, Pb (0.5-1.0 mM), or Al (2.5-5.0 mM). Finally, it is the first report of siderophore-producing microorganisms from polluted soil of Callejón de Huaylas highlands, interestedly they displayed metabolic properties useful to enhance phytoremediation and biotechnology application.

Influence of phosphorus on copper phytoextraction via modulating cellular organelles in two jute (Corchorus capsularis L.) varieties grown in a copper mining soil of Hubei Province, China

Soil in mining areas is typically highly contaminated with heavy metals and lack essential nutrients for plants. Phosphorus reduces oxidative stress, improves plant growth, composition, and cellular structure, as well as facilitates the phytoremediation potential of fibrous crop plant species. In this study, we investigated two jute (Corchorus capsularis) varieties HongTieGuXuan and GuBaChangJia cultivated in copper (Cu)-contaminated soil (2221 mg kg^-1), under different applications of phosphorus (0, 30, 60, and 120 kg ha^-1) at both anatomical and physiological levels. At the same Cu concentration, the tolerance index of HongTieGuXuan was higher than that of GuBaChangJia, indicating that HongTieGuXuan may be more tolerant to Cu stress. Although the normal concentration of P (60 kg ha^-1) in the soil improved plant growth, biomass, chlorophyll content, fibre yield and quality, and gaseous exchange attributes. However, high concentration of P (120 kg ha^-1) was toxic to both jute varieties affected morphological and physiological attributes of the plants under same level of Cu. Moreover, Cu toxicity increased the oxidative stress in the leaves of both jute varieties was overcome by the activities of antioxidant enzymes. Furthermore, the high concentration of Cu altered the ultrastructure of chloroplasts, plastoglobuli, mitochondria, and many other cellular organelles in both jute varieties. Thus, phytoextraction of Cu by both jute varieties increased with the increase in P application in the Cu-contaminated soil. This suggests that P application enhanced the phytoremediation potential jute plants and can be cultivated as fibrous crop in Cu-contaminated sites.