Preventative effect of crop straw-derived biochar on plant growth in an arsenic polluted acidic ultisol

Effect of iron-loaded sludge biochar amendments on phytoremediation potential of Cr-contaminated soils by Leersia hexandra swartz

In this study, the effect of iron-loaded sludge biochar (ISBC) with different amendment dosages (mass ratio of biochar to soil equal to 0, 0.01, 0.025 and 0.05) on the phytoremediation potential of Leersia hexandra swartz (L. hexandra) to Cr-contaminated soil was investigated. With increasing ISBC dosage from 0 to 0.05, plant height, aerial tissue biomass and root biomass increased from 15.70 cm, 0.152 g pot-1 and 0.058 g pot-1 to 24.33 cm, 0.304 g pot-1 and 0.125 g pot-1, respectively. Simultaneously, the Cr contents in aerial tissues and roots increased from 1039.68 mg kg-1 to 2427.87 mg kg-1 to 1526.57 mg kg-1 and 3242.62 mg kg-1, respectively. Thus, the corresponding bioenrichment factor (BCF), bioaccumulation factor (BAF), total phytoextraction (TPE) and translocation factor (TF) values were also increased from 10.52, 6.20, 0.158 mg pot-1 (aerial tissue)/0.140 mg pot-1 (roots) and 0.428 to 15.15, 9.42, 0.464 mg pot-1 (aerial tissue)/0.405 mg pot-1 (roots) and 0.471, respectively. The significant positive effect of ISBC amendment was primarily attributed to the following three aspects: 1) the root resistance index (RRI), tolerance index (TI) and growth toxicity index (GTI) of L. hexandra to Cr were increased from 100%, 100% and 0%-216.88%, 155.02% and 42.18%, respectively; 2) the bio-available Cr content in the soil was decreased from 1.89 mg L-1 to 1.48 mg L-1, while the corresponding TU (toxicity units) value was declined from 0.303 to 0.217; 3) the activities of urease, sucrase and alkaline phosphatase in soil were increased from 0.186 mg g-1, 1.40 mg g-1 and 0.156 mg g-1 to 0.242 mg g-1, 1.86 mg g-1 and 0.287 mg g-1, respectively. In summary, ISBC amendment was able to significantly improve the phytoremediation of Cr-contaminated soils by L. hexandra.

Role of biochar-based free radicals in immobilization and speciation of metals in the contaminated soil-plant environment

The structure of biochar produced at various pyrolysis temperatures influences metal geochemical behavior. Here, the impact of wheat straw-derived biochar (300, 500, and 700 °C) on the immobilization and transformation of metals in the contaminated soil-plant system was assessed. The findings of the sequential extraction revealed that biochar additives had a substantial influence on the speciation of Cr, Ni, Pb, and Zn in the contaminated soil. The lowest F1 (exchangeable and soluble fraction) + F2 (carbonate fraction) accounted for Cr (44%) in WB-300, Ni (43.87%) in WB-500, Pb (43.79%), and Zn (49.78%) in WB-700 with applied amendments of their total amounts. The characterization results indicated that high pyrolysis temperatures (300-700 °C) increased the carbon-containing groups with the potential to adsorb metals from the soil-plant environment. The bioconcentration and translocation factors (BCF and TF) were less than 1, indicating that metal concentration was restricted to maize roots and translocation to shoots. Reactive oxygen species (ROS) intracellularly influence metal interactions with plants. Electron paramagnetic resonance (EPR) was performed to determine hydroxyl radical generation (•OH) in plant segments to assess the dominance of free radicals (FRs). Consequently, the formation of •OH significantly depends on the pyrolysis temperature and the interaction with a contaminated soil-plant environment. Thus, metal transformation can be effectively decreased in the soil-plant environment by applying WB amendments.

Laboratory study of water infiltration and evaporation in biochar-amended landfill covers under extreme climate

Biochar has been used as an environment-friendly enhancer to improve the soil hydraulic properties. Previous studies focused on the effect of biochar addition for irrigation in agricultural soils. However, the understanding of the influence of biochar addition on water infiltration in compacted soils as used in landfill covers is limited. This study investigated the effects of peanut shell biochar addition on soil water infiltration with consideration of soil microstructure variations. The performance of biochar-amended soil was also explored under extreme rainfall and drought conditions. In this experiment, peanut shell biochar with particles finer than 0.25 mm was amended into compacted silty sand. Index soil properties and microstructure were observed. One-dimension (1-D) column tests and corresponding numerical modelling were carried out to investigate the performance of this cover material under different climate scenarios. The results suggested that the application of biochar can increase soil porosity, but a significant number of large pores (i.e., larger than 20 μm) was minimized. With the application of biochar, the soil covers thus become more efficient in preventing infiltration and percolation. This is also crucial to minimize the need for a relatively large thickness of soil cover. With an increase in porosity, the biochar can improve the soil water retention. Under extreme drought, the application of biochar can reduce the very low pore-water pressure (PWP) in soils by more than 50%. From all of these, peanut shell biochar can potentially be an eco-friendly and more sustainable solution for soil covers, even under extreme climate conditions.

Arsenic-Induced Oxidative Stress and Antioxidant Defense in Plants

The non-essential metalloid arsenic (As) is widely distributed in soil and underground water of many countries. Arsenic contamination is a concern because it creates threat to food security in terms of crop productivity and food safety. Plants exposed to As show morpho-physiological, growth and developmental disorder which altogether result in loss of productivity. At physiological level, As-induced altered biochemistry in chloroplast, mitochondria, peroxisome, endoplasmic reticulum, cell wall, plasma membrane causes reactive oxygen species (ROS) overgeneration which damage cell through disintegrating the structure of lipids, proteins, and DNA. Therefore, plants tolerance to ROS-induced oxidative stress is a vital strategy for enhancing As tolerance in plants. Plants having enhanced antioxidant defense system show greater tolerance to As toxicity. Depending upon plant diversity (As hyperaccumulator/non-hyperaccumulator or As tolerant/susceptible) the mechanisms of As accumulation, absorption or toxicity response may differ. There can be various crop management practices such as exogenous application of nutrients, hormones, antioxidants, osmolytes, signaling molecules, different chelating agents, microbial inoculants, organic amendments etc. can be effective against As toxicity in plants. There is information gap in understanding the mechanism of As-induced response (damage or tolerance response) in plants. This review presents the mechanism of As uptake and accumulation in plants, physiological responses under As stress, As-induced ROS generation and antioxidant defense system response, various approaches for enhancing As tolerance in plants from the available literatures which will make understanding the to date knowledge, knowledge gap and future guideline to be worked out for the development of As tolerant plant cultivars.