Pteris vittata coupled with phosphate rock effectively reduced As and Cd uptake by water spinach from contaminated soil

Arsenic-Hyperaccumulator Pteris vittata Effectively Uses Sparingly-Soluble Phosphate Rock: Rhizosphere Solubilization, Nutrient Improvement, and Arsenic Accumulation

Sparingly-soluble phosphate rock (PR), a raw material for P-fertilizer production, can be effectively utilized by the As-hyperaccumulator Pteris vittata but not most plants. In this study, we investigated the associated mechanisms by measuring dissolved organic carbon (DOC) and acid phosphatase in the rhizosphere, and nutrient uptake and gene expression related to the As metabolism in P. vittata. The plants were grown in a soil containing 200 mg kg-1 As and/or 1.5% PR for 30 days. Compared to the As treatment, the P. vittata biomass was increased by 33% to 4.6 g plant-1 in the As+PR treatment, corresponding to 27% decrease in its frond oxidative stress as measured by malondialdehyde. Due to PR-enhanced DOC production in the rhizosphere, the Ca, P, and As contents in P. vittata fronds were increased by 17% to 9.7 g kg-1, 29% to 5.0 g kg-1, and 57% to 1045 mg kg-1 in the As+PR treatment, thereby supporting its better growth. Besides, PR-induced rhizosphere pH increase from 5.0 to 6.9 promoted greater P uptake by P. vittata probably via upregulating low-affinity P transporters PvPTB1;1/1;2 by 3.7-4.1 folds. Consequently, 29% lower available-P induced the 3.3-fold upregulation of high-affinity P transporter PvPht1;3 in the As+PR treatment, which was probably responsible for the 58% decrease in available-As content in the rhizosphere. Consistent with the enhanced As translocation and sequestration, arsenite antiporters PvACR3/3;3 were upregulated by 1.8-4.4 folds in the As+PR than As treatment. In short, sparingly-soluble PR enhanced the Ca, P, and As availability in P. vittata rhizosphere and improved their uptake via upregulating genes related to As metabolism, suggesting its potential application for improving phytoremediation in As-contaminated soils.

Improved efficiency of Sedum lineare (Crassulaceae) in remediation of arsenic-contaminated soil by phosphate-dissolving strain P-1 in association with phosphate rock

The selection of appropriate plants and growth strategies is a key factor in improving the efficiency and universal applicability of phytoremediation. Sedum lineare grows rapidly and tolerates multiple adversities. The effects of inoculation of Acinetobacter sp. phosphate solubilizing bacteria P-1 and application of phosphate rock (PR) as additives on the remediation efficiency of As-contaminated soil by S. lineare were investigated. Compared with the control, both the single treatment and the combination of inoculation with strain P-1 and application of PR improved the biomass by 30.7-395.5%, chlorophyll content by 48.1-134.8%, total protein content by 12.5-92.4% and total As accumulation by 45.1-177.5%, and reduced the As-induced oxidative damage. Inoculation with strain P-1 increased the activities of superoxide dismutases and catalases of S. lineare under As stress, decreased the accumulation of reactive oxygen species in plant tissues and promoted the accumulation of As in roots. In contrast, simultaneous application of PR decreased As concentration in S. lineare tissues, attenuated As-induced lipid peroxidation and improved As transport to shoots. In addition, the combined application showed the best performance in improving resistance and biomass, which significantly increased root length by 149.1%, shoot length by 33%, fresh weight by 395.5% and total arsenic accumulation by 159.2%, but decreased the malondialdehyde content by 89.1%. Our results indicate that the combined application of strain P-1 and PR with S. lineare is a promising bioremediation strategy to accelerate phytoremediation of As-contaminated soils.

Remediation of uranium-contaminated alkaline soil by rational application of phosphorus fertilizers: Effect and mechanism

In alkaline soil, abundant carbonates will mobilize uranium (U) and increase its ecotoxicity, which is a serious threat to crop growth. However, the knowledge of U remediation in alkaline soils remains very limited. In this study, U-contaminated alkaline soil (tillage layer) was collected from the Ili mining area of Xinjiang, the soil remediation was carried out by using phosphorus (P) fertilizers of different solubility (including KH₂PO₄, Ca(H₂PO₄)₂, CaHPO₄, and Ca₃(PO₄)₂), and the pathways and mechanisms of U passivation in the alkaline soil were revealed. The results showed that water-soluble P fertilizers, KH₂PO₄ and Ca(H₂PO₄)₂, were highly effective at immobilizing U, and significantly reduced the bioavailability of soil U. The exchangeable U was reduced by 70.5 ± 0.1% (KH₂PO₄) and 68.2 ± 1.9% (Ca(H₂PO₄)₂), which was converted into the Fe-Mn oxide-bound and residual phases. Pot experiments showed that soil remediation by KH₂PO₄ significantly promoted crop growth, especially for roots, and reduced U uptake in crops by 94.5 ± 1.0%. The immobilization of U by KH₂PO₄ could be attributed to the release of phosphate anions, which react with the uranyl ion (UO₂²⁺) forming a stable mineral of meta-ankoleite and enhancing the binding of UO₂²⁺ to the soil Fe-Mn oxides. In addition, KH₂PO₄ dissolution produces acidity and P fertilizer, which can reduce soil alkalinity and improve crop growth. The findings in this work demonstrate that a rational application of P fertilizer can effectively, conveniently, and cheaply remediate U contamination and improve crop yield and safety on alkaline farmland.

Geographical distribution of As-hyperaccumulator Pteris vittata in China: Environmental factors and climate changes

Understanding the distribution of hyperaccumulators helps to implement more efficient phytoremediation strategies of contaminated sites, however, limited information is available. Here, we investigated the geographical distribution of the first-known arsenic-hyperaccumulator Pteris vittata in China and the key factors under two climate change scenarios (SSP 1-2.6 and SSP 5-8.5) at two time points (2030 and 2070). Species distribution model (MaxEnt) was applied to examine P. vittata distribution based on 399 samples from field surveys and existing specimen records. Further, among 23 environmental factors, 11 variables were used in the MaxEnt model, including temperature, precipitation, elevation, soil property, and UV-B radiation. The results show that P. vittata can grow in ~23% of the regions in China. Specifically, it is mainly distributed in 11 provinces of southern China, including Hainan, Guangdong, Guangxi, Yunnan, Guizhou, Hunan, Hubei, Jiangxi, Fujian, Zhejiang, and Jiangsu. Besides, eastern Sichuan, and southern Henan, Shaanxi, and Anhui are suitable for P. vittata growth. Under two climate change scenarios, P. vittata distribution in China would decrease by ~5.76-7.46 × 10⁴ km² in 2030 and ~3.22-4.68 × 10⁴ km² in 2070, with southern Henan and most Jiangsu being unsuitable for P. vittata growth. Among the 11 environmental variables, the minimum temperature of coldest month (bio6) and temperature annual range (bio7) are the two key factors limiting P. vittata distribution. At bio6 <-5 °C and/or bio7 >33 °C, the regions are unsuitable for P. vittata growth. Based on the MaxEnt model, precipitation had limited effects, so P. vittata can probably survive under both dry and moist environments. This study helps guide phytoremediation of As-polluted soils using P. vittata and provides an example to evaluate habitat suitability of hyperaccumulators at international scales.

Influencing factors and prediction of arsenic concentration in Pteris vittata: A combination of geodetector and empirical models

Phytoextraction using hyperaccumulator, Pteris vittata, to extract arsenic (As) from soil has been applied to large areas to achieve an As removal rate of 18% per year. However, remarkable difference among different studies and field practices has led to difficulties in the standardization of phytoextraction technology. In this study, data on As concentration in P. vittata and related environmental conditions were collected through literature search. A conceptual framework was proposed to guide the improvement of phytoextraction efficiency in the field. The following influencing factors of As concentration in this hyperaccumulator were identified: total As concentration in soil, soil available As, organic matter in soil, total potassium (K) concentration in soil, and annual rainfall. The geodetection results show that the main factors that affect As concentration in P. vittata include soil organic matter (q = 0.75), soil available As (q = 0.67), total K (q = 0.54), and rainfall (q = 0.42). The predictive models of As concentration in P. vittata were established separately for greenhouse and field conditions through multivariate linear stepwise regression method. Under greenhouse condition, soil available As was the most important influencing factor and could explain 41.4% of As concentration in P. vittata. Two dominant factors were detected in the field: soil available As concentration and average annual rainfall. The combination of these two factors gave better prediction results with R² = 0.762. The establishment of the model might help predict phytoextraction efficiency and contribute to technological standardization. The strategies that were used to promote As removal from soil by P. vittata were summarized and analyzed. Intercropping with suitable plants or a combination of different measures (e.g., phosphate fertilizer and water retention) was recommended in practice to increase As concentration in P. vittata.

Effect of iron plaque on antibiotic uptake and metabolism in water spinach (Ipomoea aquatic Forsk.) grown in hydroponic culture

Ferrous ion was added to the culture solution, followed by the introduction of tetracyclines (TCs), to explore the effect of iron plaque (IP) on the uptake and translocation of TCs by water spinach (Ipomoea aquatic Forsk.). The adsorption amount of TCs on the root surface positively correlated with the amount of IP, except for doxycycline and minocycline. The bioconcentration factor of TCs in roots increased and fitted well with the amount of IP. The concentration of TCs in acrial tissues was three to four orders of magnitude lower than that in roots, and the translocation factor of TCs also fitted well with the amount of IP in a negative linear relationship. Furthermore, IP significantly influenced the metabolism of TCs in water spinach. The accumulation of TC metabolites increased with the increment of IP in roots rather than in acrial tissues, which showed the significance of IP in the metabolism and accumulation of TCs in aquatic plants. Therefore, the metabolism of TCs should not be ignored if IP is induced on the root surface, and the distribution of metabolites should be taken into consideration for the risk assessment and antibiotic pollution control for aquatic plants.

Pteris vittata Arsenic Accumulation Only Partially Explains Soil Arsenic Depletion during Field-Scale Phytoextraction

Soil arsenic heterogeneity complicates our understanding of phytoextraction rates during arsenic phytoextraction with Pteris vittata, including in response to rate stimulation with nutrient treatments. In a 58-week arsenic phytoextraction field study, we determined the effects of soil arsenic concentrations, fertilizer application, and mycorrhizal fungi inoculation on P. vittata arsenic uptake rates, soil arsenic depletion, and arsenic soil–plant mass balances. Initial soil arsenic concentrations were positively correlated with arsenic uptake rates. Soil inoculation with mycorrhizal fungus Funneliformis mosseae led to 1.5–2 times higher fern aboveground biomass. Across all treatments, ferns accumulated a mean of 3.6% of the initial soil arsenic, and mean soil arsenic concentrations decreased by up to 44%. At depths of 0–10 cm, arsenic accumulation in P. vittata matched soil arsenic depletion. However, at depths of 0–20 cm, fern arsenic accumulation could not account for 61.5% of the soil arsenic depletion, suggesting that the missing arsenic could have been lost to leaching. A higher fraction of arsenic (III) (12.8–71.5%) in the rhizosphere compared to bulk soils suggests that the rhizosphere is a distinct geochemical environment featuring processes that could solubilize arsenic. To our knowledge, this is the first mass balance relating arsenic accumulation in P. vittata to significant decreases in soil arsenic concentrations under field conditions.

Phosphate: Coupling the functions of fertilization and passivation in phytoremediation of manganese-contaminated soil by Polygonum pubescens blume

Phosphate (P) fertilization is a commonly used agronomic practice. However, research on bioremediation is very limited. This study's principal objective was to evaluate the role of P in the growth and heavy metals (HMs) accumulation of Polygonum pubescens Blume cultured in Mn-contaminated soil. To this end, the effects of sodium dihydrogen phosphate (SDP) and single superphosphate (SSP) on the growth, Mn bioremediation efficiency, organ HMs, and physiological parameters related to antioxidant stress of P. pubescens were examined. The results showed that both SDP and SSP increased soil pH and available P but decreased available HMs. Phosphate significantly (P < 0.05) promoted P. pubescens height and biomass. Average height increased by 36.1% and 32.6% with SDP and SSP, respectively, with corresponding biomass increases of 71.8% and 135%. Phosphate significantly (P < 0.05) reduced Mn concentrations, especially in leaves, where the values decreased by >50.0% for DSP and SSP. Total Mn significantly (P < 0.05) decreased with DSP amendment but significantly (P < 0.05) increased by 38.5% with SSP (200 mg kg^-1) through an increase in biomass. Phosphate significantly (P < 0.05) decreased all organ HM concentrations and translocation, indicating that less HM stress occurred with P amendment. The changes in reactive oxygen species, antioxidants and non-antioxidant materials further supported these results. Pearson correlation analysis revealed negative relationships between soil available P and HMs, indicating a novel role of P in HM passivation. The uncommonly high Ca concentrations in leaves suggested that Ca plays a vital role in promoting growth and alleviating HM stress in P. pubescens, which warrants further study.