The impacts of exogenous phosphorus on Cd absorption in perennial ryegrass root cell: Kinetic and mechanism study.

Phosphorus (P) is critical to plants in metal-contaminated soils because it participates in various biochemical reactions during plant growth. However, the mechanisms of P in mitigating the toxicity of heavy metals to ryegrass root is still veiled. In this study, the physiological and biochemical dynamics of the ryegrass root under various cadmium (Cd) and P conditions were investigated in a hydroponic system. Cd stress decreased the length of the ryegrass root, but P application enhanced the root elongation to reduce the Cd concentration in the root. Both Cd and P dosages were positively correlated with hemicellulose 1 content, pectin content, and PME activity, while having a negative effect on cellulose content. Moreover, the addition of 80 mg L-1 P increased the contents of pectin and hemicellulose 1 by 2.5 and 5.8% even with 4 mg L-1 Cd. In addition, P supply increased pectin methylesterbase activity under Cd stress, which further changed the extra-cytoplasmic structures and cell wall composition. Thus, exogenous P promoted the immobilization of Cd onto the cell wall and protected protoplast primarily through indirectly regulating the binding capacity of the root cell wall for Cd.

Enhancing lead immobilization by biochar: Creation of "surface barrier" via bio-treatment.

The long-term effectiveness of heavy metal immobilization is always a concern. This study proposes a completely novel approach to enhance the stability of heavy metals by combined biochar and microbial induced carbonate precipitation (MICP) technology, to create a "surface barrier" of CaCO3 layer on biochar after lead (Pb2+) immobilization. Aqueous sorption studies and chemical and micro-structure tests were used to verify the feasibility. Rice straw biochar (RSB700) was produced at 700 °C, which shows high immobilization capacity of Pb2+ (maximum of 118 mg g-1). But the stable fraction only accounts for 4.8% of the total immobilized Pb2+ on biochar. After MICP treatment, the stable fraction of Pb2+ significantly increased to a maximum of 92.5%. Microstructural tests confirm the formation of CaCO3 layer on biochar. The CaCO3 species are predominantly calcite and vaterite. Higher Ca2+ and urea concentrations in cementation solution resulted in higher CaCO3 yield but lower Ca2+ utilization efficiency. The main mechanism of the "surface barrier" to enhance Pb2+ stability on biochar was likely the encapsulation effect: it physically blocked the contact between acids and Pb2+ on biochar, and chemically buffer the acidic attack from the environment. The performance of the "surface barrier" depends on both the yield of CaCO3 and their distribution uniformity on biochar's surface. This study shed lights on the potential application of the "surface barrier" strategy combining biochar and MICP technologies for enhanced heavy metal immobilization.

Evaluating the potential of charred bone as P hotspot assisted by phosphate-solubilizing bacteria.

The enhanced phosphorus (P) release from charred bone by microorganisms results in hotspots to alleviate P limitation in agricultural and natural systems. This study compared P release, assisted by phosphate-solubilizing bacteria (PSB), from charred bone (CB) produced at various temperatures (100-300 °C). In the absence of PSB, soluble P from CB in water was observed with fluctuation between 100 and 300 °C, with a maximum value of 8.66 mg/L at 200 °C. Similarly, kinetics of dissolution indicated that CB produced at 250 °C owned the highest solubility and dissolution rate. After the addition of PSB, soluble P from all the CB samples were all elevated. The CB produced at 100 °C incredibly showed the most significant enhancement (from 3.51 to 77.37 mg /L). ATR-IR and XPS confirmed the loss of organic matter (primarily collagen), but no significant mineralogical alternation of bioapatite in bone. Meanwhile, it demonstrated that collagen itself cannot provide soluble P. However, the collagen contributed to the substantial sorption of bacteria, which improved the efficiency of P release from CB surface. This study clarified the P release via the interaction between CB and PSB, and hence provided a new perspective on understanding P biogeochemical cycle in ecosystem.