Copper uptake, physiological response, and phytoremediation potential of Brassica juncea under biochar application.

Biochar can enhance the phytoremediation of copper-contaminated soils by improving soil quality and increasing plant growth. However, the impact of biochar varies with the biomass feedstock and soil condition. Our study investigated the effect of biochar from orange bagasse-OBB and coconut husk-CHB and two copper concentrations (0.17 mg kg-1-CLS soil; 100 mg kg-1- CTS soil) on plant growth, copper uptake, and physiological response of Brassica juncea. The low- and high-Cu soils were also tested without biochar. We evaluated plant biomass, plant Cu, N and P, chlorophyll content, and chlorophyll's transient fluorescence. Plant growth was meager without biochar, indicating that the high Cu concentration was not the only limiting factor. Biochar (OBB and CHB) increased shoot mass by 300-574% and root mass by 50-2900%, and improved chlorophyll content and photosynthetic activity by 6-16%. Both biochars were efficient in the low-Cu soil as they increased plant biomass, shoot copper concentration, and translocation factor. In the high-Cu soil, both biochars increased plant biomass and copper uptake and reduced shoot copper concentration and translocation factor. The CHB and OBB removed 342% and 783% more Cu from the contaminated soil than the Control; therefore, the OBB was proven to be the best choice for phytoremediation.Novelty statement Our study showed that the orange bagasse biochar can be successfully applied for the phytoremediation of copper-contaminated soils using Brassica juncea. The orange bagasse biochar was effective regardless of the copper level in the soil, removing twice as much copper as the coconut biochar; therefore, it can speed up the process and reduce the time needed to clean up the site. HighlightsBiochar significantly improved the plant's physiological responseBiochar increased plant growth and copper uptake in the contaminated soilTranslocation factor was increased in the clean soil and reduced in the contaminated soilBiochar from orange bagasse is more effective than coconut husk for phytoremediation.

Aged biochar changed copper availability and distribution among soil fractions and influenced corn seed germination in a copper-contaminated soil.

Biochar has been recommended as a multi-beneficial amendment for the in situ remediation of heavy metals contaminated soils due to its high recalcitrance, stability, specific surface area and retention capacity, which leads to a long-lasting influence on the immobilization of soil contaminants. The influence of biochar on the availability of heavy metals such as copper is not fully understood and may be related to a change in copper association with soils fractions. Therefore, a long-time laboratory incubation study was set up as a completely randomized design to test the effect of biochar from different sources (coconut husks-CHB, orange bagasse-OBB and sewage sludge-SSB) at two rates of application (30 and 60 t ha-1) on the distribution of copper in a copper-contaminated soil after 24 months incubation. Copper distribution was evaluated through a sequential extraction procedure that fractionated copper into five fractions: F1 (soluble and exchangeable), F2 (specifically bound), F3 (organic matter bound), F4 (Fe and Mn oxide bound) and F5 (residual). Copper availability, soil pH and organic matter were also evaluated. Corn seeds were germinated in the incubated biochar soil to investigate the effect of biochar on seed germination and plantlets characteristics. All biochars increased soil pH and the concentration of oxidizable organic matter, and reduced copper availability after the 24 months incubation. CHB caused a discrete influence on copper distribution among soil fractions. OBB30 increased F1 (54.5%), F3 (24.0%), F4 (32.2%) and F5 (64.1%), and reduced F2 (39.8%); OBB60 reduced F1 (61.8%), F2 (16.5%) and F3 (16.0%) and increased F4 (18.0%) and F5 (84.4%). SSB30 strongly reduced Cu concentration in F1 (96.2%), F2 (34.0%), and F3 (22.2%), and increased F4 (54.4%); SSB60 reduced F1 (57.5%) and F3 (59.4%). Considering the high stability of biochar, the association of copper to the organic fraction leads to a long-time reduction in copper availability in the contaminated soil, which can reduce the cost and increase the efficiency of the remediation process. SSB reduced seed germination but produced vigorous and well-developed plantlets. Therefore, with proper production procedure to reduce the volatile matter content, SSB may not interfere with seed germination and has the greatest potential to be used for the remediation of copper-contaminated sites.

Nitrogen and phosphorus uptake efficiency in Indian mustard cultivated during three growth cycles in a copper contaminated soil treated with biochar / Eficiência de absorção de nitrogênio e fósforo em mostarda indiana cultivada por três ciclos sucessivos em um solo contaminado com cobre e tratado com biocarvão

ABSTRACT: Biochar has been used worldwide as an efficient soil amendment due to its beneficial interaction with soil particles and nutrients; however, studies on the effect of biochar on the availability of nutrients such as N and P in tropical soils are still missing. The objective of the study was to evaluate the effect of different types and doses of biochars on the concentration and uptake of N and P in Indian mustard plants (Brassica juncea L.) grown in a Cu contaminated soil during three successive growth cycles. The greenhouse experiment was set up as randomized block design in a 3x3 factorial scheme, with 3 types of biochars (coconut shell, orange bagasse and sewage sludge) and three rates of application (0, 30 and 60t ha-1), and 4 replicates. Biochar increased plant growth by approximately 30 to 224%; however, the orange bagasse biochar was the most effective. Biochar reduced plant N concentration in approximately 15-43%, regardless of the rate of application, indicating the need to carefully adjust N fertilization. In the last growth cycle, biochar from coconut shell and orange bagasse improved the N uptake efficiency suggesting a better amelioration effect with ageing in soil. Biochar did not affect P nutrition in Indian mustard to a great extent; however, it significantly decreased the N:P ratio in the plant.

RESUMO: O biocarvão tem sido usado mundialmente como um eficiente insumo agrícola devido à sua interação benéfica com as partículas e os nutrientes do solo. Contudo, seu efeito na disponibilidade de nutrientes como N e P em solos tropicais tem sido pouco investigado. O objetivo do estudo foi avaliar o efeito de diferentes tipos e doses de biocarvão na concentração e na eficiência de absorção de N e P em plantas de mostarda indiana (Brassica juncea L.) cultivadas em solo contaminado com cobre, em três ciclos sucessivos de cultivo. O estudo foi desenvolvido em delineamento de blocos casualizados, em esquema fatorial 3x3, em casa de vegetação, com três tipos de biocarvão (casca de coco, bagaço de laranja e lodo de esgoto) e três doses (0, 30 e 60t ha-1). Todos os biocarvões aumentaram o crescimento das plantas, com variação de 30 a 224%. No entanto, o biocarvão de bagaço de laranja foi o mais eficiente. A presença de biocarvão reduziu a concentração de N nas plantas em torno de 14 a 43%, independente da dose aplicada, indicando a necessidade de monitoramento mais cuidadoso da fertilização nitrogenada. Os biocarvões de casca de coco e bagaço de laranja melhoraram a eficiência da planta na absorção de N no terceiro ciclo de cultivo, indicando melhor efeito com o tempo de contato como o solo. O uso de biocarvão teve pouca influência na nutrição fosfatada na mostarda indiana, mas diminuiu significativamente a relação N:P.

Assessing biochar applications and repeated Brassica juncea L. production cycles to remediate Cu contaminated soil.

Copper contamination and toxicity in soils is a worldwide problem, especially in areas where copper-based fungicides are applied. Indian mustard (Brassica juncea L.) plants are used in phytoremediation and are also edible crops commonly cultivated in organic agricultural areas. Application of biochar to Cu contaminated soils may reduce Cu availability and uptake, thereby allowing for greater Indian mustard production. A (3 × 2) + 1) experiment in a randomized complete block design was used to evaluate the effect of three different biochars (coconut shell, orange bagasse and sewage sludge) and two application rates (30 and 60 t ha-1) on Cu uptake by Indian mustard during three successive growth cycles and Cu immobilization in soil, under greenhouse conditions. Coconut husk biochar did not influence available soil Cu; however, its presence increased shoot Cu uptake by 117% and 38% in the two last growth cycles. Orange bagasse biochar, at the 60 t ha-1 application rate, reduced Cu availability, but it was not effective in reducing Cu uptake. Sewage sludge biochar did not affect Cu availability and caused an approximated 100% increase in shoot Cu uptake at the highest application rate. Therefore, the orange bagasse biochar is the most effective whereas the sewage sludge biochar is the least in Cu immobilization. None of the biochars was shown to be suitable as soil amendment to reduce the uptake of Cu by Indian mustard. However, coconut shell and sewage sludge biochar can be effectively applied to soil as an auxiliary tool to remediate Cu-contaminated soils.

Predicting arsenic bioavailability to hyperaccumulator Pteris vittata in arsenic-contaminated soils.

Using chemical extraction to evaluate plant arsenic availability in contaminated soils is important to estimate the time frame for site cleanup during phytoremediation. It is also of great value to assess As mobility in soil and its risk in environmental contamination. In this study, four conventional chemical extraction methods (water, ammonium sulfate, ammonium phosphate, and Mehlich III) and a new root-exudate based method were used to evaluate As extractability and to correlate it with As accumulation in P. vittata growing in five As-contaminated soils under greenhouse condition. The relationship between different soil properties, and As extractability and plant As accumulation was also investigated. Arsenic extractability was 4.6%, 7.0%, 18%, 21%, and 46% for water, ammonium sulfate, organic acids, ammonium phosphate, and Mehlich III, respectively. Root exudate (organic acids) solution was suitable for assessing As bioavailability (81%) in the soils while Mehlich III (31%) overestimated the amount of As taken up by plants. Soil organic matter, P and Mg concentrations were positively correlated to plant As accumulation whereas Ca concentration was negatively correlated. Further investigation is needed on the effect of Ca and Mg on As uptake by P. vittata. Moreover, additional As contaminated soils with different properties should be tested.

Rhizosphere characteristics of two arsenic hyperaccumulating Pteris ferns.

Better understanding of the processes controlling arsenic bioavailability in the rhizosphere is important to enhance plant arsenic accumulation by hyperaccumulators. This greenhouse experiment was conducted to evaluate the chemical characteristics of the rhizosphere of two arsenic hyperaccumulators Pterisvittata and Pterisbiaurita. They were grown for 8 weeks in rhizopots containing arsenic-contaminated soils (153 and 266 mg kg(-1) arsenic). Bulk and rhizosphere soil samples were analyzed for water-soluble As (WS-As) and P (WS-P), pH, and dissolved organic carbon (DOC). Comparing the two plants, P.vittata was more tolerant to arsenic and more efficient in arsenic accumulation than P.biaurita, with the highest frond arsenic being 3222 and 2397 mg kg(-1). Arsenic-induced root exudates reduced soil pH (by 0.74-0.92 units) and increased DOC concentrations (2-3 times) in the rhizosphere, resulting in higher WS-P (2.6-3.8 times higher) compared to the bulk soil. Where there was no difference in WS-As between the rhizosphere and bulk soil in soil-153 for both plants, WS-As in the rhizosphere was 20-40% higher than those in bulk soil in soil-266, indicating that the rate of As-solubilization was more rapid than that of plant uptake. The ability to solubilize arsenic via root exudation in the rhizosphere and the ability to accumulate more P under arsenic stress may have contributed to the efficiency of hyperaccumulator plants in arsenic accumulation.