No abstract

Microcrystalline cellulose (MCC) is regarded as a potential filler in the fabrication of epoxy composites. However, MCC’s hydrophilic nature and strong hydrogen bonds caused by abundant surface hydroxyl groups greatly weaken its compatibility with the epoxy resin. In addition, it remains a challenge to efficiently and heterogeneously modify MCC surface hydroxyl groups. In this work, MCC was epoxidized heterogeneously with a phase-transfer catalyst. Results indicated that 4.48% (by mass) or 58.15% (by coverage) of the hydroxyl groups on MCC was modified. The dispersibility of epoxidized MCC (EP-MCC) in the epoxy resin was significantly improved. At the same time, EP-MCC showed the ability to interact with the epoxy network covalently, improving the interface interactions, indicating the simultaneous enhancement of the modulus and the toughness. As a result, this heterogenous epoxidation method showed high efficiency in reducing the surface hydroxyl content of MCC, endowing it with a bright future in industrial applications of epoxy composites.

Arbuscular mycorrhizal fungi (AMF) exist widely in soil polluted by heavy metals and have significant effects on plant growth and cadmium (Cd) uptake. Cd contents differ among wasteland, farmland and slopeland soils in a lead-zinc mining area in Yunnan Province, Southwest China. The effects of AMF on maize growth, root morphology, low-molecular-weight organic acid (LMWOA) concentrations and Cd uptake were investigated via a root-bag experiment. The results show that AMF increased maize growth on Cd-polluted soils, resulting in increases in root length, surface area, volume and branch number, with the effects being stronger in farmland than in wasteland and slopeland soils; increased malic acid and succinic acid secretion 1.3-fold and 1.1-fold, respectively, in roots on farmland soil; enhanced the iron- and manganese-oxidized Cd concentration by 22.6%, and decreased the organic-bound Cd concentration by 12.9% in the maize rhizosphere on farmland soil; and increased Cd uptake 12.5-fold and 1.7-fold in shoots and by 25.7% and 86.6% in roots grown on farmland and slopeland soils, respectively. Moreover, shoot Cd uptake presented significant positive correlations with root surface area and volume and LMWOA concentrations. Thus, these results indicated the possible mechanism that the increased maize Cd uptake induced by AMF was closely related to their effect on root morphology and LMWOA secretion, with the effects varying under different Cd pollution levels.

Arbuscular mycorrhizal fungi (AMF) are widely present in heavy metal-polluted soils, but their effects on straw degradation and plant growth of rotated crops are poorly understood. In this study, a pot experiment was used to simulate the return of fore-rotating crop (Brassica napus L.) straw to farmland with a subsequent planting of maize in a lead–zinc mining area on the Yunnan Plateau, Southwest China, which included four treatments: control (CK), addition of rape straw (SR), inoculation of AMF (AMF), and both AMF inoculation and straw addition (AMF + SR). The effects of AMF on the degradation and nutrient release of the fore-rotating rape straw and the growth, mineral nutrition and the cadmium (Cd) and lead (Pb) contents of the subsequent maize were investigated. Compared with the CK treatment, AMF significantly promoted the degradation of rape straw and the release of mineral nutrients (nitrogen, phosphorus and potassium) as well as the Cd and Pb, increased the content of available nutrients in soil, and improved the mineral nutrient contents in the maize. AMF + SR significantly increased the maize height and biomass by 32–35% and decreased the available Cd and Pb contents in soil and the Cd and Pb contents in the maize by 20–30% and 18–25%, respectively. Moreover, the available Cd and Pb contents in the soil presented significant positive correlations with their contents in the maize but negative correlations with the height and biomass of the maize. Thus, AMF played an important regulatory role in the nutrient cycling and heavy metal accumulation of the crop rotation.

Arbuscular mycorrhizal fungi (AMF) exist widely in soils polluted by heavy metals and have significant effects on plant growth and cadmium (Cd) uptake. There are three land-use types (wasteland, farmland and mountain) with different Cd pollution levels in a lead-zinc mining area in Huize County, Yunnan Province, Southwest China. The effects of AMF on the growth, root morphology and exudate content, rhizosphere Cd speciation and Cd uptake by maize were investigated via a root-bag experiment. The results showed that AMF increased the height and biomass of maize grown soils of the three land-use types, resulting in increases in root length, surface area, volume and branch number, and its effects were higher on maize grown on farmland soil than on wasteland and mountain soils. AMF increased the malic acid and succinic acid contents secreted by maize roots in farmland and mountain soils, enhanced the contents of iron and manganese oxidized Cd, and decreased the content of organic bound Cd in the maize rhizosphere. Moreover, AMF increased Cd uptake in shoots by 12.5 and 1.7 times, and improved Cd uptake in roots by 25.7% and 86.6%, in farmland and mountain soils, respectively. Correlation analysis showed that the Cd uptake in shoots was significantly or significantly positively correlated with the root surface area and root volume and with the contents of the tartaric acid, malic acid and succinic acid secreted by the roots. Thus, the increased maize Cd uptake promoted by AMF was closely related to its affecting root morphology and low molecular weight organic acid secretion, and its effects varied among soils of land-use types with different Cd pollution levels.