Non-mining Ecotype Research Articles

Differences in Physiological Metabolism and Antioxidant System of Different Ecotypes of Miscanthus floridulus under Cu Stress

To reveal the similarities and differences in the resistance mechanisms of different ecotypes to Cu stress, a pot experiment was used to systematically compare the physiological responses of non-mining ecotype Miscanthus floridulus (collected from Boluo County, Huizhou City) and mining ecotype Miscanthus floridulus (collected from Dabaoshan mining area) under different Cu concentrations. The results showed that chlorophyll a, chlorophyll b and total chlorophyll in the leaves of the two ecotypes of M. floridulus were negatively correlated with Cu stress concentration (p < 0.01), but the extent of decrease for the ecotypes in the mining area was lower than that for the ecotypes in the non-mining area. The values of chlorophyll a/b for both ecotypes increased with increasing Cu treatment concentration, indicating that Cu is more harmful to chlorophyll b than to chlorophyll a for M. floridulus. Cu stress can lead to the accumulation of malondialdehyde (MDA) in the leaves of M. floridulus with the amount of MDA accumulation observed being greater in the non-mining ecotype than in the mining ecotype (p < 0.05). The content of antioxidant substances (ascorbic acid and reduced glutathione) in the mining ecotype M. floridulus was significantly higher than that in the non-mining ecotype. The activity of SOD in the leaves of non-mining ecotypes was inhibited by Cu stress and the activity of POD was increased by Cu stress. However, the increase in POD in the mining ecotypes was greater than that in the non-mining ecotypes and the activities of the two enzymes in the mining ecotypes were significantly higher than those in the non-mining ecotypes at the highest concentration of Cu. Cu had different effects on PPO activity in the leaves of the two ecotypes of M. floridulus. The plant leaves of the non-mining ecotype at 400 and 800 mg·kg−1 were significantly fewer than those of the control group (p < 0.05), which were 87.1% and 65.2% of the control group, respectively. The PPO activity in the plant leaves of the mining ecotype was higher than that in the leaves of the non-mining ecotype and was significantly higher at 400 and 800 mg·kg−1 than that of the control group (p < 0.05), at 226.5% and 268.1% of the control group, respectively. These results indicate that the mining ecotype M. floridulus is more resistant to copper stress, that resistant ecotypes have been formed, and that small-molecule antioxidant substances play an important role in increasing resistance levels.

The Difference of Lead Accumulation and Transport in Different Ecotypes of Miscanthus floridulus

Miscanthus floridulus is a plant with a high biomass and heavy metal tolerance, which is a good candidate for phytoremediation. Pot experiments were conducted to compare the growth response, Pb enrichment ability, and the effect on Pb speciation of two ecotypes of M. floridulus from the Dabaoshan Mining Area and the non-mining area of Boluo County, Huizhou, in soils with different Pb contents. The results showed that two ecotypes of M. floridulus had different growth responses to Pb concentrations in soil. Under a low concentration of Pb (100 mg·kg−1) treatment, the aboveground biomass of the non-mining area plant ecotype was significantly affected, while the plants with the mining area ecotype were not significantly affected. When the concentration of Pb increased, the aboveground biomass of the non-mining ecotype was 30.2–41.1% of the control, while that of the mining ecotype was 57.8–65.0% of the control. The root biomass of the non-mining ecotype decreased with the increase of treatment concentration, accounting for 57.8–64.2% of the control, while that of the mining ecotype increased significantly, accounting for 119.5–138.6% of the control. The Pb content in the shoots and roots of the mining ecotype M. floridulus increased rapidly with the increase of the Pb treatment concentration in the soil, and the increase in speed was obviously faster than that of the non-mining ecotype. The total amount of Pb accumulated in the roots of the ecotype from the mining area was much greater than that of the ecotype from the non-mining area, and increased significantly with the increase of Pb concentration in the soil (p < 0.05). With the aggravation of Pb stress, the transfer coefficient and tolerance index of the two ecotypes decreased by different degrees. The transfer coefficient and tolerance index of the mining ecotype were significantly higher than those of the non-mining ecotype. Pearson correlation analysis showed that root biomass was positively correlated with shoot biomass, and shoot biomass was negatively correlated with Pb content in both root and shoot, indicating that Pb accumulation in root and shoot was toxic to plants and inhibited the growth of M. floridulus. The mining ecotypes showed stronger tolerance to and enrichment of Pb.

Indigenous rhizosphere microbial community characteristics of the phytostabilizer Athyrium wardii (Hook.) grown in a Pb/Zn mine tailing

Plant rhizosphere microbiome usually changes dramatically in adaptation to the mine environment to endure high heavy metal concentration, which in turn improves the process of revegetation and phytostabilization of mine tailing and deserves deep investigation. A field study was conducted to investigate the indigenous microbial community of a mining ecotype (ME) of the phytostabilizer Athyrium wardii (Hook.) grown in a Pb/Zn mine tailing and a corresponding non-mining ecotype (NME) grown in an uncontaminated adjacent site. Our study found a slight difference in microbial α-diversity between the ME and NME, and no significant difference between the rhizosphere and bulk soil. Both bacterial and fungal community compositions differed between the ME and NME, for which the differences were mainly driven by pH and metal contaminants. The ME harbored a unique microbial community in the rhizosphere soils different from the bulk soil and NME counterparts. The dominant phyla in the ME rhizosphere were Proteobacteria, Chloroflexi, Actinobacteria, Nitrospirae, and Ascomycota. Several genera from Proteobacteria, Acidobacteria, and Ascomycota were more abundant in the ME rhizosphere than in the NME rhizosphere. Network analysis revealed that keystone taxa were different in the two sites. Some keystone taxa from Gemmatimonadaceae, and Burkholderiaceae and Ascomycota played a critical role in microbial interactions within the mine tailing network. The unique microbial community with high tolerance in the rhizosphere soils of ME may show great benefit for plant growth and metal tolerance of the ME and thereby contributing to the process of revegetation and phytostabilization of mine tailings.

Sufficient nitrogen promoted high phosphorus tolerance and phosphorus-accumulating capability of Polygonum hydropiper in relation to changes of phytohormones and phenols

Nitrogen (N) application is efficient to enhance phosphorus (P)-phytoextraction efficiency of P-accumulating plants. However, there is little available information on growth, P uptake and physiological changes of P-accumulating plants in high P media with different N application, and that whether the improved growth or P uptake is related with changes of phytohormones and phenols. This study investigated growth, P-accumulating capability, phytohormones and phenols of a mining ecotype (ME) and a non-mining ecotype (NME) of Polygonum hydropiper in high P media (400 mg L−1) with sufficient N (SN, 50 mg L−1) and low N (LN, 12.5 mg L−1) supply. SN supply greatly increased tissue biomass, P-accumulating capability of P. hydropiper in high P media, and the ME showed higher P bioaccumulation coefficient, and tissue P accumulation than the NME. The greatest tissue biomass and P accumulation was found at 5 weeks. At 5 weeks, SN supply greatly decreased concentrations of indole-3-acetic acid (IAA), zeatin, abscisic acid (ABA), total phenolic and flavonoid in tissues of P. hydropiper, compared with LN supply. The ME produced lower concentrations of IAA, zeatin, ABA, total phenolic and flavonoid than the NME in leaf and stem in high P media with N supply. Significantly negative correlations were found between IAA, zeatin, ABA, flavonoid concentrations and biomass as well as P accumulation in leaf. Thus, SN supply promoted high P tolerance and P-accumulating capability of the ME in relation to modulating phytohormones and phenols to suitable concentrations, ultimately improving P-phytoextraction ability.

Characterization of dissolved organic matter in the rhizosphere of phytostabilizer Athyrium wardii (Hook.) involved in enhanced metal accumulation when exposed to Cd and Pb co-contamination

The characterization of DOM and its effect on heavy metal solubility in soils have been widely concerned, while few concerns on the phytostabilization of multi-metal contaminated soils. A pot experiment was performed to characterize dissolved organic matter (DOM) in the rhizosphere of the mining ecotype (ME) and non-mining ecotype (NME) of Athyrium wardii (Hook.) when exposed to Cd and Pb simultaneously, and investigate its effect on Cd and Pb solubility in soils. The ME presented more DOM in the rhizosphere when exposed to Cd and Pb simultaneously than that exposed to single Cd or Pb, and also than the NME. The acid fractions (hydrophilic acid, hydrophobic acid) and hydrophilic fractions (hydrophilic acid, hydrophilic neutral, and hydrophilic base) were the dominant parts of DOM in the ME rhizosphere. The ME presented more acid and hydrophilic fractions in the rhizosphere when exposed to Cd and Pb simultaneously. Meanwhile, there were more O–H, C–O, N–H and C–H, assigned to carboxylic groups, phenolic groups, hydroxyl groups, and/or amino groups, present in DOM from the rhizosphere of ME when exposed to Cd and Pb simultaneously. These results highlighted the acid characteristics of DOM in the rhizosphere of ME when exposed to Cd and Pb simultaneously. DOM in the rhizosphere of ME thereby showed greater complexation degree for Cd (68%) and Pb (77%), thus showing greater ability to enhance Cd and Pb solubility in soils when exposed to Cd and Pb simultaneously. This is thereby considered to be one of the key processes for enhancing Cd and Pb uptake by the ME when exposed to Cd and Pb simultaneously.

Characteristics of bacterial community in root-associated soils of the mining ecotype of Polygonum hydropiper, a P-accumulating herb

Polygonum hydropiper is a phosphorus (P)-accumulating herb used for P-phytoextraction, with higher P-accumulating capability in the mining ecotype (ME) than the non-mining ecotype (NME). This difference might result from the variation in root-associated soil (rhizoplane, rhizosphere) bacterial characteristics. Thus, characteristics and influence factors of bacterial community were investigated in root-associated soils and bulk soils of both ecotypes of P. hydropiper in situ using high-throughput sequencing technique. Bacterial community diversity and richness were independent with ecotypes; rather it positively correlated with soil organic matter concentration. Forty-nine phyla were identified, with Proteobacteria being the most dominated phylum. Soil bacterial community compositions were primarily separated into clusters by ecotypes, simultaneously with great influence by soil groups and chemical properties. Rhizoplane and rhizosphere bacterial communities showed more similarity compared with those in bulk soil. Soil pH, available P, available nitrogen and available potassium played major roles in shaping the bacterial community compositions. The genera Halomonas, Flavisolibacter, Blastocatella, Thiobacillus, Sphingomonas and Bacillus in ME root-associated soils showed higher abundance than in NME root-associated soils, positively with soil available P concentration, suggesting these genera might be important in mobilizing soil mineral-P and facilitating P uptake for the ME of P. hydropiper.

The combined effects of Cd and Pb enhanced metal binding by root cell walls of the phytostabilizer Athyrium wardii (Hook.)

Cell wall acts as a major metal sink in plant roots, while a few studies focused on root cell wall binding in plants for the phytostabilization of multi-metal contaminated soils. A pot experiment was performed to characterize root cell wall properties of the mining ecotype (ME) and non-mining ecotype (NME) of Athyrium wardii (Hook.) in response to Cd and Pb. The cell wall was found to be the major sink for Cd (41.3–54.3%) and Pb (71.4–73.8%) accumulation in roots of the ME when exposed to Cd and/or Pb. The ME showed more Cd and Pb accumulation in root cell walls when exposed to Cd and Pb simultaneously, compared with those exposed to single Cd or Pb as well as the NME, suggesting some modifications for cell walls. The uronic acid contents of pectin and hemicellulose 1 (HC1) in root cell walls of the ME increased significantly when exposed to Cd and Pb simultaneously, suggesting enhanced cell wall binding capacity, thus resulting in more Cd and Pb bound to pectin and HC1. In particular, pectin was found to be the predominant binding site for Cd and Pb. Greater pectin methylesterase activity along with a lower degree of methylesterification were observed in the cell walls of the ME when exposed to Cd and Pb simultaneously. Furthermore, the ME present more O–H, N–H, C–OH, C–O–C, C–C and/or Ar–H in root cell walls when exposed to Cd and Pb simultaneously. These changes of root cell wall properties of the ME lead to enhanced cell wall binding ability in response to the co-contamination of Cd and Pb, thus could be considered a key process for enhanced Cd and Pb accumulation in roots of the ME when exposed to Cd and Pb simultaneously.

Lead accumulation and soil microbial activity in the rhizosphere of the mining and non-mining ecotypes of Athyrium wardii (Hook.) Makino in adaptation to lead-contaminated soils.

Better understanding of microbial activity in the rhizosphere soils associated with lead (Pb) uptake by plants may help with the phytoremediation of Pb-contaminated soils. In this work, the effects of Pb exposure (0, 200, 400, 600, 800 mg kg-1) on Pb accumulation and soil microbial activity in the rhizosphere of the mining ecotype (ME) and corresponding non-mining ecotype (NME) of Athyrium wardii (Hook.) Makino were investigated through a pot experiment. Although the plant growth of the two ecotypes was inhibited under Pb stress, the ME showed a less biomass decrease (12.6-44.0%) for aboveground than the NME, showing a greater tolerance to Pb stress. Pb concentrations as well as Pb accumulation in the two ecotypes showed an increasing trend with increasing soil Pb concentrations. The ME presented greater Pb accumulation ability than the NME, especially in underground parts. Pb availability in the rhizosphere soils of the two ecotypes after harvest decreased compared with those before transplantation. Available Pb in the rhizosphere of the ME was 1.4-4.8 times higher than that of the NME under exposure to 200-800 mg kg-1 Pb. The ME shows a greater ability to mobilize Pb in the rhizosphere soils. Pb exposure resulted in an inhibition of microbial activity in the rhizosphere of the two ecotypes. The ME demonstrated greater soil respiration and microbial biomass carbon (MBC) in the rhizosphere than the NME when treated with 200-800 mg kg-1 Pb. The ME showed a less decrease for MBC and a less increase for metabolic quotient in the rhizosphere soils than the NME when exposed to Pb generally. Microorganisms in the rhizosphere soils of the ME seem to be much more adapted to Pb stress, thus showing a great benefit for Pb accumulation and the phytostabilization of Pb-contaminated soils by the ME.

Subcellular distribution and chemical forms involved in manganese accumulation and detoxification for Xanthium strumarium L.

Xanthium strumarium L. is a candidate species for manganese (Mn)-phyto-remediation. To reveal the mechanism of this species adaptive to Mn stress, the growth, Mn subcellular distribution, chemical forms, as well as micro-structure and ultra-structure responses of the mining ecotype (ME) of X. strumarium to Mn stress were studied with the non-mining ecotype (NME) as the reference by a hydroponic experiment. The results showed the ME demonstrated a higher tolerance to Mn stress with a superior growth and a higher tolerance index (TI) when compared with the NME. The concentrations of Mn in leaves, stems, and roots of the ME were 1.1–1.8, 1.2–1.9, and 1.3–1.9 times higher than those in the corresponding organs of the NME, respectively. The micro-structure and ultra-structure showed abnormal alterations, such as shrunken ducts and sieve canals, round-shaped chloroplasts, increased starch and osmiophilic granules, as well as expanded and non-compact granum thylakoids in the NME, compared to the ME. More than 83% of Mn was localized in cell wall and soluble fraction, while the Mn concentration in all fractions had a direct linear relationship with Mn treatment in the ME. The proportions of pectates and protein integrated-Mn, phosphate-Mn, and oxalate-Mn forms were dominant in leaves and stems of the ME, whereas, in the NME the relative proportions of inorganic Mn and water-soluble Mn forms in the roots was higher than the other forms. Altogether, the combination of preferential distribution of Mn in the cell wall and soluble fraction, and storage of Mn in low toxicity forms, such as phosphate-Mn, pectates and protein-bound Mn, and oxalate-Mn, might be responsible for alleviating Mn toxicity in the ME.

Changes in P accumulation, tissue P fractions and acid phosphatase activity of Pilea sinofasciata in poultry manure-impacted soil

Pilea sinofasciata is a promising phytoextraction material to remove excess phosphorus (P) from manure-impacted soil. However, little information is available on its physiological response to animal manure treatments. Here, P accumulation, tissue P fractions and acid phosphatase activity were investigated in a mining ecotype (ME) and a non-mining ecotype (NME) of P. sinofasciata at different poultry manure (PM) treatments (0, 25, 50, 75, 100 and 125 g kg−1). Biomass and P accumulation of the ME increased up to 50 g kg−1, after which they significantly decreased; while P accumulation of the NME increased up to 100 g kg−1. But, shoot and root P accumulation of the ME were significantly higher than those of the NME at all PM treatments, showing 1.13–2.92 and 1.11–2.89 times higher values, respectively. Inorganic P and nucleic P dominated in tissues of both ecotypes. Besides, the ME maintained higher concentrations of inorganic P and ester P in leaves and ester P, nucleic P and residual P in roots than the NME. Acid phosphatase activity in leaves and roots increased by increasing PM treatments, except in root at 125 g kg−1. Acid phosphatase activity in leaves of the ME was positively correlated with concentrations of inorganic P, ester P and nucleic P, while that of the NME only correlated with inorganic P concentration. Probably, the optimized P fractions allocation and higher tissue acid phosphatase allow the ME to grow well and efficiently accumulate P in PM-impacted soil.

Cd and Pb accumulation characteristics of phytostabilizer Athyrium wardii (Hook.) grown in soils contaminated with Cd and Pb.

Interactions between heavy metals in soil could affect soil heavy metal availability and plant uptake. Thus, in this study, Cd and Pb accumulation as well as plant growth of the mining ecotype (ME) and non-mining ecotype (NME) of Athyrium wardii (Hook.) in response to the exposure of Cd and Pb was investigated by a pot experiment. Although the exposure of Cd in combination with Pb further inhibited the growth of the two ecotypes in comparison with the exposure of single Cd or Pb, the ME presented lower biomass decline for the whole plant (22.0%-70.0%) than the NME among most treatments. The presence of Pb promoted Cd accumulation both in above-ground and under-ground parts of the ME. Cd concentrations in under-ground parts of the ME decreased when exposed to higher concentrations of Pb (> 600mgkg-1). Meanwhile, the presence of Cd inhibited Pb accumulation in above-ground parts of the ME and promoted Pb accumulation in under-ground parts of the ME. Pb concentrations in under-ground parts of the ME decreased when soil Cd concentrations were more than 25mgkg-1. The partial correlation analysis further demonstrated that the interactions between Cd and Pb stimulated Cd accumulation both in above-ground and under-ground parts of the ME and Pb accumulation in under-ground parts of the ME, while inhibited Pb accumulation in above-ground parts of the ME, showing great benefit for Pb phytostabilization by the ME. Among treatments, the bioaccumulation coefficients for Cd and Pb of the ME, varying from 2.71-31.05 and 20.09-78.06, were much higher than those of the NME. The translocation factors for Cd and Pb of the ME, varying from 0.26-0.52 and 0.01-0.10, were lower than those of the NME. These results indicate that the ME presented greater potential for the phytostabilization of soil contamination with Cd and Pb, especially for Pb.

Phosphorus accumulation characteristics in Polygonum hydropiper and rhizosphere properties affected by poultry manure application

Land-applied poultry manure threatens to water environments, particularly because of its high concentration of phosphorus (P). Polygonum hydropiper is efficient in extracting soil excess P, thereby reducing the risk of P runoff and leaching. Rather, little is understood about the effects of poultry manure on soil properties and the P-accumulating characteristics of this plant species. Two pot experiments were conducted to investigate P accumulation and rhizosphere properties in a mining ecotype (ME) of P. hydropiper from Shifang phosphate-mining area and the contrasting non-mining ecotype (NME), with the first experiment at different poultry manure application rates (0, 25, 50, 75, 100 g kg−1 dry soil) and the second experiment under the optimum poultry manure concentration (75 g kg−1) over three growth periods. The ME’s shoot biomass and P accumulation increased with poultry manure application rates up to 75 g kg−1 and increased with increasing growth periods. Shoot biomass and P accumulation of the ME were significantly greater than those of the NME at 75 g kg−1 in both experiments. At the optimum poultry manure rate (75 g kg−1), H2O-Pi (Pi, inorganic P), H2O–, NaHCO3− and NaOH-Po (Po, organic P) were more depleted in ME rhizosphere than NME rhizosphere whereas NaHCO3− and NaOH-Pi increased more in ME rhizosphere than NME rhizosphere, irrespective of growth periods. Soil acid and alkaline phosphatases, phosphodiesterase and phytase activities of the ME significantly increased with manure rates up to 75 g kg−1. Higher enzymatic activities were observed in poultry manure soil than the control and in the rhizospheric soil than bulk soil. The ME showed significantly greater activities of rhizospheric acid phosphatase and phytase than the NME in poultry manure soil at 8 weeks, when its P accumulation showed the largest increase. Therefore, the ME can extract much greater P than the NME from poultry manure-amended soil, probably through the changes in its rhizosphere properties.

P uptake characteristics and root morphological responses in the mining ecotype of Polygonum hydropiper under high organic P media

ABSTRACTUnderstanding plant phosphorus (P) assimilation and its root morphological responses is important to acquire an ideal material for remediation of P-enriched environments. Pot experiments were conducted to explore P accumulation and root morphological traits in a mining ecotype (ME) and non-mining ecotype (NME) of Polygonum hydropiper under different organic P (Po) sources (G1P, AMP, ATP, IHP) and inorganic P (Pi) source (KH2PO4), and also their responses to a high level of IHP for different growth periods. Both ecotypes showed higher biomass in Pi and IHP treatments than other Po sources. P accumulation in seedlings were in the order of Pi > IHP > other Po media. Extending the growth period increased biomass and P accumulation in both ecotypes. The ME demonstrated 1.11–1.46 times higher P accumulation than the NME. Seedlings fed with IHP demonstrated significantly greater morphological parameters of fine, medium, and thick roots compared to other Po sources. Total root length, surface area, and volume of both ecotypes significantly increased with the prolonged growth period. The ME has a higher ability to develop root system and exhibits better distribution of fine roots to enhance P accumulation from high P media, and thus it is a worthy material for P-phytoextraction.

Rhizosphere characteristics of phytostabilizer Athyrium wardii (Hook.) involved in Cd and Pb accumulation

Soil contamination with Cd and Pb shows interactive effects on rhizosphere microenvironment and further uptake of Cd and Pb by plants. Thus, the rhizosphere characteristics of the mining ecotype (ME) and non-mining ecotype (NME) of Athyrium wardii in response to Cd and Pb was investigated through a pot experiment in this study. Compared with Cd or Pb alone, the contamination of Cd and Pb inhibited the growth of the two ecotypes of A. wardii, and ME presented lower decrease of 56.22% and 55.07% for above-ground part biomass than NME. The combination of Cd and Pb promoted Cd accumulation both in above-ground and under-ground parts of ME, as well as Pb accumulation in under-ground parts of ME, with the increase of 92.68%, 102.77% and 35.87%, respectively. As a result, increased bioaccumulation coefficients (BCF) for Cd and Pb and decreased translocation factors (TF) for Pb of ME were observed when exposed Cd and Pb. ME presented much greater BCF values for Cd and Pb, and much lower TF values for Cd and Pb than NME. The rhizosphere soil pH of ME with the exposure of Cd and Pb reduced by 0.12–0.13 units compared with single Cd or Pb. The dissolved organic carbon (DOC) concentrations in rhizosphere soils of ME exposed to Cd and Pb increased in comparison with single Cd or Pb, and ME showed greater increase (53.31–59.00%) than NME. These suggested that pH reduction and exudation of greater amounts of DOC may have contributed to the promotion of Cd and Pb accumulation in ME. In addition, the combination of Cd and Pb inhibited soil microbial biomass carbon (MBC) and soil respiration (SR) of A. wardii compared with Cd or Pb alone. However, greater MBC and SR, and lower metabolic quotients were found in rhizosphere soils of ME when exposed to Cd and Pb. ME showed better soil biophysical conditions in rhizosphere soils when exposed to Cd and Pb. These improvements presented great benefit for ME to phytostabilize soils co-contaminated with Cd and Pb.

Subcellular distribution and chemical form of phosphorus involved in alleviating phosphorus toxicity of the phosphorus-accumulator Polygonum hydropiper

Polygonum hydropiper is a dominant plant species in Shifang phosphorus (P) mine area and is a promising P-accumulator used for P-phytoextraction. To date, little information is available on the physiological response involved in alleviating P toxicity of P. hydropiper under high P. A pot experiment was carried out to investigate growth, P subcellular distribution, chemical forms in two ecotypes of P. hydropiper under high levels (1, 4, and 8 mmol P L−1) of inorganic P (Pi) and organic P (Po), supplied as KH2PO4 and myo-inositol hexaphosphoric acid dodecasodium salt, respectively. The mining ecotype (ME) showed a greater ability to tolerate high P than the non-mining ecotype (NME), as shown by its superior growth with undamaged leaf anatomical structure. The ME showed 1.3–2.2 times greater shoot P accumulation than the NME. More than 93% of P accumulated in tissue cell wall and soluble fraction. The increasing P treatments increased all tissue P forms, especially Pi form. The ME showed significantly higher ester P, nucleic P and insoluble P in tissues than the NME at 8 mmol L−1; however, it demonstrated lower Pi, expect for roots at 5 weeks. The percentages of Pi and nucleic P in roots of the ME were higher than other P forms, and the percentages of nucleic P dominated in the leaves. Probably, the combination of preferential distribution of P in cell wall and soluble fraction in tissues and storage of P in low activity as nucleic P in leaves allows the ME to adapt high P.

Rhizosphere P composition, phosphatase and phytase activities of Polygonum hydropiper grown in excess P soils

This study investigated phosphorus (P) accumulation and rhizosphere characteristics of Polygonum hydropiper under high levels (400, 800, and 1600 mg P kg−1) of inorganic P (Pi) and organic P (Po), supplied as KH2PO4 and myo-inositol hexaphosphoric acid dodecasodium salt, respectively. Mining (ME) and non-mining (NME) ecotypes were used since they differed in the capacity of nutrient acquisition. Biomass and P accumulation in shoots and roots of the ME increased by increasing Pi levels, whereas they decreased by increasing Po concentrations. Rhizosphere pH declined by 0.15–0.45 U for the ME and 0.04–0.14 U for the NME. Orthophosphate was the most abundant form, and it depleted greatly in the rhizosphere, with higher effect by the ME than by the NME. Glycerophosphate and inositol hexakisphosphate concentrations increased in the rhizosphere under high Po treatments with higher effect by the ME than by the NME. Rhizosphere acid phosphomonoesterase, alkaline phosphomonoesterase, and phytase activities of both ecotypes were higher in high P treatments than the treatment without P, whereas phosphodiesterase activity decreased. Significantly higher enzyme activities were observed in the rhizosphere soil of the ME than the NME. Probably, the ME might obtain higher shoot P than the NME from P-enriched soils through changes in rhizosphere properties.

Pb Uptake and Phytostabilization Potential of the Mining Ecotype of Athyrium wardii (Hook.) Grown in Pb‐Contaminated Soil

Phytostabilization has been proposed as a cost‐effective remediation strategy to immobilize metals in heavy metal polluted soils. A pot experiment was conducted to evaluate the Pb uptake characteristics and phytostabilization potential of the mining ecotype (ME) of Athyrium wardii and the corresponding non‐mining ecotype (NME) when exposed to the Pb contaminated soils for 40 days. The ME was more tolerant to Pb than the NME when grown in Pb contaminated soil, and the ME demonstrated a greater Pb accumulation ability in roots (30.6–175.45 mg plant−1) than the NME (0.85–25.59 mg plant−1). The bioaccumulation coefficients of ME ranging from 52.02 to 83.16 were 3.24–8.89 times higher than those of the NME under Pb treatment, and the translocation factors of ME ranging from 0.022 to 0.079 were <1. The ME showed a higher capability in absorbing available Pb in soil than the NME. Furthermore, Pb remediation factors in roots of the ME were 6.93–15.35 times higher than those of the NME, and the plant effective number in roots of the ME ranging from 5.70 to 12.74 were lower than those of the NME. These results indicated that the ME showed a greater Pb uptake and phytostabilization potential than the NME, which enabled it as a worthy candidate for Pb phytostabilization.

The influence of humic substance on Cd accumulation of phytostabilizer Athyrium wardii (Hook.) grown in Cd-contaminated soils.

The application of organic amendments into heavy metal contaminated soil is considered as an environmentally friendly technique to promote the potential of phytoremediation. A pot experiment was carried out to evaluate the effect of humic substances on growth, cadmium (Cd) accumulation and phytostabilization potential of the mining ecotype (ME) and the corresponding non-mining ecotype (NME) of Athyrium wardii (Hook.) grown in Cd-contaminated soils. The addition of the humic substances demonstrated great promotion for the growth and Cd uptake of ME. Both plant biomass and Cd concentration significantly increased with the increasing application of the humic substances up to 100gkg(-1), beyond which no significant change of underground part biomass and Cd concentrations in underground part of A. wardii was observed. The maximum Cd concentration in underground part of ME was 180mgkg(-1) when 150gkg(-1) humic substances were applied. The ME showed greater Cd accumulation capability in underground part (0.47-0.68mgplant(-1)) than that of NME (0.27-0.45mgplant(-1)). Increasing bioaccumulation coefficient (BCF) values of A. wardii was observed with increasing application of the humic substances. The BCF values of ME were higher than those of NME. However, the use of the humic substances exhibited little impact on translocation factors (TFs) of ME, and the TF values of ME were less than NME. Furthermore, the application of the humic substances improved the remediation factors (RFs) of A. wardii. The RF values in underground part of ME ranging from 0.73 to 0.91% were apparently higher than those of NME. These results indicated that the humic substances can be a potential candidate for enhancing the phytostabilization of A. wardii grown in Cd-contaminated soils.

Rhizosphere characteristics of Pb phytostabilizer Athyrium wardii (Hook.) involved in Pb accumulation

A pot experiment was conducted to evaluate the rhizosphere characteristics of the mining ecotype (ME) of Athyrium wardii and the non-mining ecotype (NME) with rhizobags when exposed to Pb-contaminated soils for 40 days. The results showed that the ME was more tolerant to Pb and more efficient in Pb uptake than the NME. Available Pb concentrations in the rhizosphere of ME and NME increased by 1.2–2.3 times and 1.7–2.7 times when compared to those in the bulk soil, whereas available Pb concentrations in rhizosphere of ME were lower than those of NME. Significant depletion of exchangeable Pb, Pb bound to carbonate and Pb bound to organic matter was observed in the rhizosphere of ME. No statistical change of Pb bound to Fe–Mn oxides was observed in the rhizosphere of both ecotypes. pH values in the rhizosphere of ME decreased by 0.02–0.16 units compared to the bulk soil, and the dissolved organic carbon concentrations in the rhizosphere of ME were 1.1–1.5 times higher than those in the bulk soil. Microorganism numbers in rhizosphere of both ecotypes reduced with increasing Pb treatments, and the sensitivity order of microbial community to Pb was: bacteria > fungi > actinomycetes. Microorganism number in the rhizosphere of ME was higher than that of NME and bulk soil. In conclusion, the ME was more effective in Pb uptake and showed greater capability in mobilizing Pb from non-mobile fraction to mobile fractions likely due to its specific rhizosphere characteristics.

Enhanced P accumulation characteristics and P removal potentials of Pilea sinofasciata grown under P enriched soils supplied with nitrogen

Phytoextraction is an attractive method to extract excess soil P. However, most of the potential P accumulators have relatively low P removal potential when used for extracting excess soil P. An important question then is how can we improve the P uptake capability of P accumulators? This study was conducted to investigate the effects of different nitrogen (N) treatments (0–350mgNkg−1) on growth, P accumulation characteristics, and P removal potentials of P. sinofasciata. A mining ecotype (ME) and a non-mining ecotype (NME) were grown for 9 weeks in P enriched soils affected by different N treatments. The pot survey revealed that two ecotypes of P. sinofasciata showed significant increases in shoot biomass and P accumulation with ascending N supplied up to a level of 140mgNkg−1, beyond which a notable decrease was found. The ME demonstrated greater shoot biomass and P accumulation than the NME. The P extraction ratio in shoot of the ME reached 15.92% under 140mgNkg−1, and increased by 30.08% compared with that of NME. Shoot P removal of the ME reached 29.58mgkg−1 under 140mgNkg−1 which was higher than the NME. The ME and NME both showed high levels of P removal from soil, maximum potential yield, and P removal potential after the addition of N. In conclusion, both ecotypes of P. sinofasciata show high P accumulation and P removal from N impacted soils, and thus P. sinofasciata is a potential and worthy candidate for phytoextraction.