Effects of the Dark Septate Endophyte (DSE) Exophiala pisciphila on the Growth of Root Cell Wall Polysaccharides and the Cadmium Content of Zea mays L. under Cadmium Stress

This paper aims to investigate the mechanism by which dark septate endophytes (DSEs) enhance cadmium (Cd) tolerance in there host plants. Maize (Zea mays L.) was inoculated with a DSE, Exophiala pisciphila, under Cd stress at different concentrations (0, 5, 10, and 20 mg·kg⁻¹). The results show that, under 20 mg/kg Cd stress, DSE significantly increased maize biomass and plant height, indicating that DSE colonization can be utilized to increase the Cd tolerance of host plants. More Cd was retained in DSE-inoculated roots, especially that fixed in the root cell wall (RCW). The capability of DSE to induce a higher Cd holding capacity in the RCW is caused by modulation of the total sugar and uronic acid of DSE-colonized RCW, mainly the pectin and hemicellulose fractions. The fourier-transform spectroscopy analysis results show that carboxyl, hydroxyl, and acidic groups are involved in Cd retention in the DSE-inoculated RCW. The promotion of the growth of maize and improvement in its tolerance to Cd due to DSEs are related to restriction of the translocation of Cd from roots to shoots; resistance of Cd uptake Cd inside cells; and the increase in RCW-integrated Cd through modulating RCW polysaccharide components.

Arbuscular mycorrhizal fungi reduce cadmium leaching from polluted soils under simulated heavy rainfall

Cadmium (Cd)-polluted soils were collected from wasteland, farmland, and slopeland surrounding a lead-zinc mine in Yunnan Province, Southwest China. Maize plants (the host) were inoculated with arbuscular mycorrhizal fungi (AMF) in a dual-compartment cultivation system that included mycorrhizal and hyphal compartments as part of an AMF inoculation treatment and root and soil compartments as part of a the non-inoculation treatment. The effects of AMF on maize biomass and Cd uptake, soil aggregate composition, and Cd concentration in the interflow within two soil layers (0-20 and 20-40 cm) as well as the Cd leaching from these three Cd-polluted soils under simulated heavy rainfall (40 and 80 mm/h) were investigated. The results demonstrated that AMF led to increased maize biomass and Cd uptake. There were greater contents of total glomalin-related soil protein (T-GRSP) and >2.0 mm aggregates and lower Cd concentrations in the interflow and lower dissolved Cd leaching in the mycorrhizal and hyphal compartments than in the soil compartment. A two-way analysis of variance revealed that AMF significantly increased the contents of T-GRSP and >2.0 mm aggregates and reduced both Cd concentrations in the interflow and dissolved Cd leaching. Moreover, AMF interacted extensively with the roots and affected soil aggregate composition and Cd concentrations in the interflow. Under 40 mm/h of rainfall, the contents of T-GRSP and >2.0 mm aggregates were significantly negatively correlated with both Cd concentrations in the interflow and dissolved Cd leaching. In addition, the Cd concentrations in the interflow were significantly positively correlated with the amount of dissolved Cd leaching. Therefore, both AMF-reduced Cd concentrations in the interflow and Cd leaching from Cd-polluted soils were closely related to increased T-GRSP contents and macroaggregate proportion in the soils.

Effect of root exudates of intercropping Vicia faba and Arabis alpina on accumulation and sub-cellular distribution of lead and cadmium

A field experiment in which a hyperaccumulator (Arabis alpina) was intercropped with winter crop (Vicia faba), was conducted to understand effect of the root exudates on the content and accumulated amounts, sub-cellular distribution of Cd and Pb of the intercropped plants during the ripening period of V. faba (120 d after sowing). The results showed that contents of soluble sugars exuded from the roots of intercropped A. alpina were 67.6% less than that of the monocropped plant, whereas contents of free amino acids was 57.9% greater. The total contents of organic acids exuded from roots of intercropped A. alpina and V. faba were 578.8% and 37.8% greater than that of monocropped plants, respectively. The contents of tartaric acid and malic acid exuded by roots of intercropped A. alpina were greater 31.9 times and 15.9 times than those of monocropped A. alpina, respectively. The contents and accumulated amounts of Cd and Pb in intercropped A. alpina were greater than those of monocropped A. alpina. The contents of Pb bound to organic matter in cell walls, cytoplasm and organelles of intercropped plants were greater than those of monocropped plants. These results demonstrate that increases in accumulated amounts of Pb and Cd caused by intercropping were closely related to migration of Cd and Pb in plants mediated by the composition and content of the root exudates.

[Source Apportionment of Heavy Metals in Farmland Soils Around Mining Area Based on UNMIX Model]

Forty-two farmland soil samples were collected from the mining area of Huize City, Yunnan Province, to identify the sources of metals in the farmland soils, and 14 selected elements in farmland soils were detected. The UNMIX model was applied to identify the sources of the metals. The inverse distance weighted interpolation method of statistical analysis in ArcGIS was used to develop a spatial distribution map of the six severely polluted metals to validate the source apportionment results of the UNMIX model. The results indicated that:① the metals, Pb, Zn, and Cd, in the studied farmland soils were seriously polluted according to the soil background values of Yunnan Province and the Chinese environmental quality standard; ② there were three potential sources of metals according to UNMIX model:source 1 was the anthropogenic sources caused by industrial activities with a source contribution rate of 16.32%; source 2 was the anthropogenic sources caused by coal combustion and fertilization with a source contribution rate of 68.26%; and source 3 was the combined sources caused by mining related activities and soil parent materials with a source contribution rate of 15.42%; and ③ the spatial distribution of selected metals was in accordance with the local land-use and the results of the UNMIX model. Therefore, the UNMIX model can be effectively applied to the source apportionment of heavy metals in farmland soils around the mining area.