Intercropping efficiency of four arsenic hyperaccumulator Pteris vittata populations as intercrops with Morus alba

Intercropping of Pteris vittata and maize on multimetal contaminated soil can achieve remediation and safe agricultural production

Soil contamination by multimetals is widespread. Hyperaccumulator-crop intercropping has been confirmed to be an effective method for arsenic (As)- or cadmium (Cd)-contaminated soil that can achieve soil cleanup and agricultural production. However, the influencing factors and response of hyperaccumulator-crop intercropping to multimetal-contaminated soil are still unclear. In this study, intercropping of the As hyperaccumulator Pteris vittata and maize was conducted on two typical types of multimetal-contaminated soil, namely, Soil A contaminated by As, Cd, and lead (Pb) and Soil B contaminated by As, Cd, and chromium (Cr). Intercropping reduced As, Cd, and Pb in the maize grains by 60 %, 66.7 %, and 20.4 %, respectively. The concentrations of As, Cd, Pb, and Cr in P. vittata increased by 314 %, 300 %, 447.3 %, and 232.6 %, respectively, relative to their concentrations in the monoculture plants. Two soils with different levels of contamination showed that higher heavy metal content might diminish the ability of intercropping to reduce soil heavy metal risk. No notable difference in soil microbial diversity was found between the intercropped and monocultured plants. The composition of microbial communities of intercropping groups were more similar to those of monoculture P. vittata on two different soils (Soils A and B). An imbalance between the amount of As taken up by the plants and the reduction in As in the soil was observed, and this imbalance may be related to watering, As leaching, and heterogeneity of soil As distribution. Reducing the risk resulting from As leaching and enhancing the efficiency of phytoextraction should be emphasized in remediation practices.

Influence of biochar on the arsenic phytoextraction potential of Pteris vittata in soils from an abandoned arsenic mining site

Biochar (BC) has a strong potential for activating arsenic (As) in soil; thus, the phytoremediation efficiency of As-polluted soils is enhanced with Pteris vittata L. A pot experiment was conducted to investigate the potential of BC to assist in phytoremediation with P. vittata. The effects of BC on physicochemical properties, available As, enzyme activities, and the bacterial community in the rhizosphere soil were investigated, and the biomass, physiology, and As uptake of P. vittata were analyzed. The results indicated that applying BC facilitated available As in the P. vittata rhizosphere soil, and the phytoremediation efficiency percentage increased in the As-polluted soils, such as 3.80% and 8.01% under the 2% and 5% BC treatments compared to the control, respectively. Phytoremediation with P. vittata and BC significantly improved soil organic matter content, available N, P, and K, enzyme activities, and the bacterial community. BC promoted Streptomyces (26.6-54.2%) and Sphingomonas (12.3-30.8%) abundance which regulated the growth and As uptake by P. vittata. Moreover, applying BC increased the biomass, and As uptake by P. vittata. Overall, BC strengthened the phytoremediation of As-polluted soils by improving soil pH, nutrient concentrations, enzyme activities, bacterial community structure, and soil arsenic activation, growth, and absorption by P. vittata.

The effect of exogenous plant growth regulators on elevated Cd phytoremediation by Solanum nigrum L. in contaminated soil

Maximizing amendment potential is an emphasis in the HM-contaminated field of phytoremediation by hyperaccumulators due to the low bioavailability of HMs in soils and small biomass yields of plants. This study investigated the influence of different types and concentrations of plant growth regulators on Cd phytoremediation by Solanum nigrum in contaminated soil. Our conclusions showed that the shoot Cd extractions (μg plant-1) and the root and shoot biomasses at all the treatments remarkedly increased compared with that of the CK (p < 0.05), while the Cd concentrations at root and aboveground parts by S. nigrum, the extractable Cd concentrations, and pH value of soils did not change significantly compared with the CK (p < 0.05). Furthermore, correlation analysis showed that the shoot Cd phytoaccumulation and the root and aboveground biomasses of S. nigrum were particularly dependent upon the application of CTK and GA3 concentration gradient (p < 0.05). Moreover, some related physicochemical indexes were determined for supervising the growth conditions of plants, and these results pointed out that after exogenous PGRs treatments, the chlorophyll content and antioxidative enzymes POD and SOD activities in vivo of plants clearly advanced, while the H2O2 and MDA contents and CAT apparently declined. These consequence demonstrated that the exogenous PGR addition prominently reinforced the Cd phytoextraction capacity of S. nigrum in contaminated soil by stimulating plant growth and increasing shoot yields.

Manganese-modified biochar promotes Cd accumulation in Sedum alfredii in an intercropping system

Intercropping of crops with hyperaccumulators is a sustainable method to remediate contaminated soil without impeding agro-production. However, the function of engineered biochar in intercropping systems and its possible influence on cadmium (Cd) accumulation in hyperaccumulators remain unknown. A root box experiment on celery and Sedum alfredii with and without root separation was conducted in this study. Pristine and KMnO₄-modified biochar (BC_Mn) were used to investigate the effects of different biochars on plant growth and Cd uptake in an intercropping system, as well as the influence of engineered biochar on Cd accumulation in hyperaccumulators. The results demonstrated that soil pH did not significantly vary with biochar application in the root separation treatment. However, BC_Mn significantly increased soil pH and thus reduced available Cd when the plant roots were not separated. Intercropping (no separation treatment) led to a 34% higher and 24% lower aboveground biomass of celery and S. alfredii, respectively, regardless of biochar addition. Compared with aboveground plant parts, plant roots exhibited more significant responses to biochar. Interestingly, intercropping may favour the phytoextraction of Cd by S. alfredii. In particular, the Cd uptake by S. alfredii roots substantially increased (118-187%), whereas that of celery roots decreased (51-71%) with BC_Mn addition, compared with other treatments. Moreover, after BC_Mn addition the accumulation of Cd in aboveground S. alfredii in the no separation treatment was 136% higher than that in the separation treatment. This was possibly related to the interaction of manganese (Mn) with Cd as well as the roots of S. alfredii. These findings provide new insights into the application of engineered biochar for phytoextraction, which is important for the efficient remediation of Cd-contaminated soils.

Phytoremediation of arsenic contaminated soil based on drip irrigation and intercropping

A directional leaching in drip irrigation along with intercropping was developed for enhanced phytoremediation of soils contaminated with arsenic (As). Spatiotemporal variations of As levels in soil and effects of irrigation eluents on As migration were analyzed in drip irrigation. Moreover, accumulated levels of As in Zea mays L. and Brassica rapa L. ssp. chinensis (the intercropping species) under drip irrigation and flood irrigation were compared to evaluate the enhancement on phytoremediation by drip irrigation. Results showed that As exhibited a directional migration in soil under drip irrigation, in which the solution of potassium dihydrogen phosphate (PDP) as the eluent significantly promoted As directional migration in soil. Compared to the flood-irrigated intercropping treatments, the As levels in crops (Brassica rapa L. ssp. chinensis) decreased significantly and that of remediating plants (Zea mays L. seedlings) increased significantly under the drip-irrigated intercropping condition. Drip irrigation coupled with intercropping dramatically reduced the risk of As contamination in crops and improved the phytoremediation of As-contaminated soil. PDP further enhanced the disparate effect of drip irrigation on As accumulation by crops and remediation plants.

Phytoextraction potential of arsenic and cadmium and response of rhizosphere microbial community by intercropping with two types of hyperaccumulators

Intercropping with hyperaccumulators/accumulators is a promising alternative to enhance phytoextraction of heavy metal(loid)s in contaminated soil. In this research, a pot experiment was conducted to evaluate the influences of intercropping As hyperaccumulator Pteris vittata L. with Cd hyperaccumulator Sedum alfredii Hance or accumulator Hylotelephium spectabile (Boreau) H. Ohba on the plant growth, As and Cd phytoextraction, and rhizosphere bacterial microbiota. The results indicated that intercropping can promote the growth of plants. The total biomass of P. vittata, S. alfredii, and H. spectabile in intercropping systems was improved by 19.9-34.1%, 16.8%, and 11.5%, respectively, in comparison with corresponding plant monoculture. The As content in rhizoid and frond of P. vittata when intercropped with S. alfredii was significantly increased by 28.3% and 19.0% (P < 0.05), respectively, as compared with P. vittata monoculture, and this treatment acquired the maximum As and Cd accumulation with 2032 μg·pot^-1 and 397 μg·pot^-1, respectively. Intercropping enhanced the soil bacterial community diversity. The genera of Lysobacter in P. vittata rhizosphere and Massilia and Arthrobacter in S. alfredii rhizosphere had higher abundance in the intercropping system of P. vittata and S. alfredii. There were significantly positive correlation relationships between Massilia and Arthrobacter with plant Cd content and Lysobacter with plant As content, indicating that they may play important roles in As and Cd phytoextraction. The results suggested that intercropping P. vittata with S. alfredii could be a potential strategy for phytoextraction of As and Cd from co-contaminated soil.

Potential evaluation of different intercropping remediation modes based on remediation efficiency and economic benefits - a case study of arsenic-contaminated soil

Hyperaccumulator-cash crop intercropping remediation is a research hotspot for heavy metal contaminated farmland, but few studies evaluated its feasibility based on practice. Field experiments and survey statistics were conducted to obtain parameters of Pteris vittata-Citrus reticulata/Zea mays intercropping, and potential of intercropping remediation was evaluated based on remediation efficiency and economic benefits. The results showed that intercropping hyperaccumulator with cash crop (especially herbs) had a certain negative effect on remediation efficiency because of the influence on planting density and harvest times of hyperaccumulator; while trees could partly alleviate this effect. Until achieving the predetermined target, the net remediation cost of P. vittata-Z. mays was 18.2 $/g As, followed by P. vittata monoculture (13.3 $/g) and P. vittata-C. reticulata (8.6 $/g). Based on the proposed evaluation model, nealy half of the P. vittata intercropping modes had low economic benefits, insufficient to compensate the cost of sacrificing remediation efficiency. Based on the data from two soil remediation projects, when net income of cash crops intercropped with As-hyperaccumulators exceeded 5865/1607 $/hm² (herbs/trees), the economic benefit of intercropping will be relatively obvious. Therefore, cash crops should be considered from three aspects: planting conditions, spatial allocation and economic benefits. Novelty statement: This work analyzed remediation efficiency and economic benefits of intercropping remediation. An economic benefit evaluation model was established to evaluate intercropping remediation modes. The selection principle and net income threshold of cash crops in intercropping was put forward for the first time.[Figure: see text]HighlightsThe selection principle of cash crops in intercropping remediation was put forward.An evaluation model of P. vittata intercropping remediation was established.The net cost of extracting 1.0 g of soil As in each remediation mode was proposed.Net income of herb/tree intercropped with P. vittata should exceed 5865/1607 $/hm².

Phytoremediation of a Highly Arsenic Polluted Site, Using Pteris vittata L. and Arbuscular Mycorrhizal Fungi

Phytoremediation is a promising green technique for the restoration of a polluted environment, but there is often a gap between lab and field experiments. The fern, Pteris vittata L., can tolerate a high soil arsenic concentration and rapidly accumulate the metalloid in its fronds. Arbuscular mycorrhizal fungi (AMF) are mutualistic fungi that form a symbiosis with most land plants' roots, improve their growth, and induce stress tolerance. This paper reports the results obtained using P. vittata inoculated with AMF, to extract Arsenic (As) from an industrial site highly contaminated also by other pollutants. Two experiments have been performed. In the first one, AMF colonized ferns were grown for two years under controlled conditions in soil coming from the metallurgic site. Positive effects on plant health and As phytoextraction and accumulation were detected. Then, considering these results, we performed a three year in situ experiment in the industrial site, to assess the remediation of As at two different depths. Our results show that the colonization of P. vittata with AMF improved the remediation process of As with a significant impact on the depth 0-0.2 m.

Heavy metal pollution in the environment and their toxicological effects on humans

Environmental pollution of heavy metals is increasingly becoming a problem and has become of great concern due to the adverse effects it is causing around the world. These inorganic pollutants are being discarded in our waters, soils and into the atmosphere due to the rapidly growing agriculture and metal industries, improper waste disposal, fertilizers and pesticides. This review shows how pollutants enter the environment together with their fate. Some metals affect biological functions and growth, while other metals accumulate in one or more different organs causing many serious diseases such as cancer. The pharmacokinetics and toxicological processes in humans for each metal is described. In summary, the review shows the physiological and biochemical effects of each heavy metal bioaccumulation in humans and the level of gravity and disquieting factor of the disease.

Strengthening role and the mechanism of optimum nitrogen addition in relation to Solanum nigrum L. Cd hyperaccumulation in soil

Solanum nigrum L. has a high potential for the remediation of Cd-contaminated soil, and nitrogen fertilizer supply is an effective method to further improve its phytoremediation potential. The soil pot culture experiment was used to explore 4 kinds of nitrogen fertilizers the best fertilizer addition concentrations and their strengthening mechanisms. The results showed that S. nigrum biomass increased with increasing N doses until 800 mg kg^-1, where the biomass reached maximum and no longer improved (p < 0.05). However, Cd concentration accumulated by S. nigrum and the extractable Cd concentration in soil did not show a significant decrease (p < 0.05). In this experiment, when N fertilizer was added at 800 mg kg^-1 (NH₄HCO₃, NH₄Cl, (NH₄)₂SO₄ and CH₄N₂O fertilizers), the biomass of the aboveground S. nigrum parts improved to the maximum under (NH₄)₂SO₄ and CH₄N₂O treatments, i.e. 5.86 g pot^-1 and 5.83 g pot^-1, increased by 5.92- and 5.89-fold, respectively (p < 0.05), compared to the controls without N fertilizers addition. At the same time, Cd phytoaccumulation in plants was elevated to 128.40 μg pot^-1 and 129.14 μg pot^-1, increased by 6.20- and 6.24-fold, respectively (p < 0.05), compared to control with no fertilizer added. The results of this experiment demonstrated that Cd phytoextraction capacity (μg pot^-1) was the strongest under (NH₄)₂SO₄ and CH₄N₂O treatments at N content of 800 mg kg^-1, when plant nutrient recovery reached the maximum, and these 2 types of nitrogen fertilizers could be utilized to remediate Cd-contaminated soil in field experiments or even in practice.

Who cares what parents think or do? Observational learning and experience-based learning through communication in rice farmers' willingness to adopt sustainable agricultural technologies in Hubei Province, China

Sustainable agricultural technologies are of great significance in fully utilizing agricultural resources and promoting agricultural production. However, the adoption rates of these technologies are often characterized as low in rural areas in China. To figure out the potential salient determinants of rice farmers' willingness to adopt sustainable agricultural technologies, this paper, by employing the multivariate probit model and ordered probit model, particularly and firstly explores the roles of observational learning and experience-based learning through communication from parents within the household on rice farmers' willingness to adopt these technologies. Results show that there are strong complementarities and substitutabilities between sustainable agricultural technologies that rice farmers are willing to adopt, and that observational learning and experience-based learning through communication within the household do have pronounced effects on rice farmers' willingness to adopt some sustainable agricultural technologies and on their intensive use intentions. Therefore, while formulating policies to improve the adoption rates and adoption intensity of these technologies, relevant government agencies should take the complementarities and substitutabilities between sustainable agricultural technologies as well as observational learning and experience-based learning through communication from parents into consideration.

Complementarity of co-planting a hyperaccumulator with three metal(loid)-tolerant species for metal(loid)-contaminated soil remediation

Co-planting with multiple plant species has great value for the remediation of soil co-contaminated with metal(loid)s. A pot experiment has been conducted to study the growth, phytoextraction of metal(loid) and complementarity by co-planting Pteris vittata L. with three metal(loid)-tolerant species with large biomass (namely Arundo donax L., Morus alba L., and Broussonetia papyrifera L.) on soil co-contaminated with As, Cd, Pb, and Zn. The results showed that the co-planting can favor the growth and uptake of As in hyperaccumulator P. vittata L., and improve comprehensive extraction of metal(loid). The total biomass and content of As in the roots of P. vittata L. under the co-planting system were significantly (p < 0.05) improved by 117.5% and 122.0%, respectively, compared with that in monoculture, while the content of As, Cd, Pb and Zn in the tissues of A. donax L., M. alba L. and B. papyrifera L. was slightly increased. The comprehensive accumulation amounts for As, Cd, Pb, and Zn by the four plants co-planting in contaminated soil were higher than that in part of plant's monoculture. Moreover, availability of As, Cd, and Zn in the contaminated soil was decreased in the co-planting system, meanwhile soil urease and acid phosphatase activities in soil significantly (p < 0.05) promoted as compared to the monocultures. The results suggested that positive interaction between hyperaccumulator and three metal(loid)-tolerant species can effectively enhance the growth of P. vittata L., regulate the comprehensive metal(loid)s accumulation capacity, and improve the environmental quality of contaminated soil, which drives high phytoremediation potential for metal(loid)s-contaminated soil by the co-planting.