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Afforestation is an effective approach for restoring degraded ecological functions in the dry-hot valleys of southwest China. Afforestation can affect soil carbon and nitrogen storage; however, how it affects soil P fractions, and their driving factors. is poorly understood in this region. To address these questions, we conducted a field study of Leucaena leucocephala plantations at three different stand age sites (3, 10, and 20 years) and an adjacent natural shrub-grass community control site to investigate changes in soil total phosphorus (Pt), Pi (inorganic phosphorus), Po (organic phosphorus), and phosphorus (P) fractions and their driving factors. Soil Pt, Po, labile P, and moderately labile P significantly increased in the Leucaena leucocephala plantation compared with the natural shrub grass site, and the Leucaena leucocephala plantation increased soil Pt content by significantly increasing soil Po. Soil Pt, Po, Pi, labile P, moderately labile P and non-labile P were not significantly different among the different stages of the Leucaena leucocephala plantation, and soil Pt and its fractions were all significantly higher in the middle-age forest stage of the Leucaena leucocephala plantation. These results indicate that Leucaena leucocephala plantations increased the soil P transformation ability, and soil Po played a critical role in sustaining soil P availability. The middle-age forest stage of Leucaena leucocephala plantations had the best conditions for P stocks and P conversion capacity. The abundance of actinomycetes and fungi showed significant positive relationships with soil Pi fractions (NaHCO3-Pi, NaOH-Pi, and NaOHu.s.-Pi); soil Pt and moderately labile P were significantly and directly influenced by fungal abundance. Soil organic carbon (SOC), NH4+-N, and NO3−-N showed significant and positive relationships with the soil Pi fractions (NaHCO3-Pi, NaHCO3-Po, and HCl-Po). SOC and NO3−-N were the key drivers of soil Pt, labile P, moderately labile P and non-labile fractions. These results indicate that abiotic and biotic factors differently affected the soil P fractions and Pt in Leucaena leucocephala plantations in the dry-hot valley. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) pollution in aqueous solution has caused great threat to human health. A novel chitosan and biochar supported sulfide-modified nZVI composite (CB-S-nZVI) was synthesized by liquid phase reduction method and applied to the removal of Cd2+ from wastewater. The synthesized materials were characterized by SEM, BET, XRD, FTIR, and zeta potential. Batch experiments showed that the optimum synthesis conditions of CB-S-nZVI were the S/Fe molar ratio of 0.56 and the Fe/BC mass ratio of 2. The removal capacity of Cd2+ by CB-S-nZVI increased with the increase of pH and reached the maximum of 249.92 mg/g at pH of 9. Among the competitive cations, Pb2+ and Cu2+ had a strong inhibition to the removal of Cd2+. The removal process of Cd2+ conformed to the pseudo-second-order kinetic model and the Freundlich model, and it was exothermic. XPS analysis suggested that the removal mechanism of Cd2+ was mainly through electrostatic attraction, precipitation, and complexation. Overall, these findings provide new insights into the development of new nZVI-modified material, and CB-S-nZVI is promising in removing heavy metals from wastewater. [ABSTRACT FROM AUTHOR]