Suppression of arbuscular mycorrhizal fungi increased lead uptake in maize leaves and loss via surface runoff and interflow from polluted farmland.

Arbuscular mycorrhizal fungi (AMF) are ubiquitous in farmland. But the knowledge on AMF impact on lead (Pb) migration in farmland is limited. A field experiment was conducted in the rainy season (May-October) for two years in a Pb-polluted farmland. Benomyl was used to specifically suppress the native AMF growth in the farmland. The effect of benomyl-induced AMF suppression on the Pb uptake in maize, and Pb loss via surface runoff and interflows (20 cm and 40 cm depth) from the farmland was investigated. The benomyl significantly inhibited the AMF growth, resulting in decreases in the colonization rate, spore number, and contents of total and easily extractable glomalin-related soil protein (GRSP); and promoted the Pb migration into maize shoots and mainly enriched in leaves. The particulate Pb accounted for 83.2%-90.6% of Pb loss via surface runoff, while the proportion of particulate Pb loss via interflow was decreased and the proportion of dissolved Pb loss increased with the increase of soil depth. The AMF suppression led to a decrease in dissolved Pb concentration and loss, but an increase in particulate Pb concentration and loss, and enhanced the total Pb loss via surface runoff and interflows. Moreover, significant or very significant negative correlations were observed between the AMF colonization rate in roots with the Pb uptake in leaves, and the content of easily extractable GRSP with the particulate Pb loss. These results indicated the native AMF contributed to immobilizing Pb in soil and inhibited its migration to crops and the surrounding environment.

Field experiment on the effects of sepiolite and biochar on the remediation of Cd- and Pb-polluted farmlands around a Pb-Zn mine in Yunnan Province, China.

The effects of sepiolite and biochar on the contents of available nutrients (N, P, and K); the chemical forms and available contents of Cd and Pb in soils; the biomass and growth of maize; and the contents of nutrients, Cd, and Pb in maize were studied in situ in Cd- and Pb-polluted farmlands around the Lanping Pb-Zn mine in Yunnan Province, China. Results demonstrated that sepiolite did not influence the contents of available nutrients in soils, although it significantly increased the pH value and decreased available Cd (CaCl2-extractable and exchangeable) contents and exchangeable and reducible Pb. Moreover, sepiolite increased the biomass in the aboveground part of maize, resulting in the reduction of Cd contents in maize plants and grains by 25.6-47.5%. Meanwhile, the biochar increased the contents of available nutrients in soils and decreased the contents of exchangeable Pb in soils and biomass in the aboveground part of maize plants and grains; decreased the Cd contents in maize stems and grains by 26.7% and 24.6%, respectively; and decreased the Pb content in roots by 16.2%. However, neither sepiolite nor biochar had considerable influence on the Pb content in maize grains. According to a correlation analysis, soil pH has extremely significant negative correlations with available Cd content in soils, which in turn have extremely significant positive correlation with the Cd content in maize plants and grains. These results revealed that sepiolite increases soil pH and decreases Cd bioavailability in farmland soils around the Pb-Zn mine. Furthermore, biochar increases the contents of available nutrients in farmland soils and the maize yield. Sepiolite and biochar both decrease the contents and transfer coefficients of Cd in maize plants and grains and are, thus, applicable to the immobilization remediation of Cd-polluted farmlands.