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The information on the effects of ZnONPs on soil biological processes and the resulting changes of ecosystem function is limited in wheat straw return agricultural soil. This study investigated the effects of ZnONPs on soil heterotrophic respiration and biochemical properties in wheat straw return farmland soil. An 84-day microcosm incubation experiment was implemented after the exposure of different doses of ZnONPs (0, 100, and 500 mg kg−1 dry soil) in a greenhouse under the temperature of 25 ± 3 °C. Soil heterotrophic respiration and soil enzyme activities were detected. Microbial community composition and diversity were analyzed by Illumina MiSeq platform. Heterotrophic respiration was significantly inhibited by ZnONPs at 500 mg kg−1. The activities of β-glucosidase, cellulose, and cellobiohydrolase decreased under high-level exposure of ZnONPs. The labile Zn2+ assimilated by soil microorganism was increased by 331% and 707%, respectively. Bacterial communities in the soil are more sensitive to ZnONPs than fungal ones. The changes of heterotrophic respiration were closely correlated with soil pH values and microbial compositions, especially fungal communities. Although ascomycetes were inhibited by ZnONPs, their abundance was the highest within soil fungal community. The inhibition of heterotrophic respiration was associated with the variation of soil fungal communities, although the bacterial communities are sensitive to ZnONPs. The microbiome modulation is necessary for the management of the decomposition of returned wheat straw in the field contaminated by ZnONPs. The effects of ZnONPs on soil ecological process should be considered when the application of fertilizers and pesticides which contain ZnONPs.

Ectomycorrhizal fungus (ECMF) is one of the important plant symbiotic fungi. Their functions in enhancing the tolerance of plants to heavy metal toxicity have been widely recognized and applied. The function mechanisms of ECMF of enhancing the tolerances of plants to heavy metal toxicity have been paid much attention. However, many previous reviews have not distinguished the effects and mechanisms on the tolerance to heavy metal toxicity between ECMF and ECMF mycorrhizae symbionts. We reviewed the response mechanisms of pure cultured ectomycorrhizal fungi under heavy metal stress in vitro, the anatomical mechanisms, the physiological mechanisms, the molecular regulation mechanisms of ectomycorrhiza tolerance to heavy metal toxicity and the enhancement of plant tolerance to heavy metal. It will shed the light on the enhancement mechanism of ECMF in the plant tolerance to heavy metal. Further research directions on the application of ectomycorrhizal fungi in the remediation of contaminated sites have been indicated.

In order to investigate the effect of ZnO nanoparticles (ZnONPs) on soil ecosystem in soil with added cellulose and lignin, five treatments were set up: cellulose, cellulose + ZnONPs, lignin, lignin + ZnONPs, and no addition. The soil respiration, microbial biomass, and the activities of soil enzymes were explored during a 56-day incubation time after the addition of ZnONPs. The results showed that when cellulose and lignin were added to the soil, the CO2 efflux increased by 90.9% and 18.2%, respectively, compared with the control soil. The microbial biomass carbon and the activity of peroxidase, polyphenol oxidase, β-glucosidase and cellulase were increased. Compared with the treatment with the addition of cellulose and lignin only, the exposure of ZnONPs increased the CO2 efflux, microbial biomass carbon, β-glucosidase and cellulase activities, but decreased the peroxidase and polyphenol oxidase activities. We concluded that the addition of cellulose and lignin to farmland soil increased respiration, microbial biomass and soil enzyme activity, but the degradation degree of cellulose was higher than lignin. The ZnONPs promote soil respiration, microbial biomass, and hydrolase activity throughout the culture period, but inhibited the activity of redox enzymes.

In order to explore the phytoremediation ability of willow in heavy metal contaminated soil and water, we studied the growth response, accumulation and translocation capacity and antioxidant enzyme activities in Salix matsudana 'J172' (A7) and Salix psammophila 'Huangpi1' (A94) under the stress of Cd (0, 15 and 30 μM) by hydroponic. The results showed that the growth inhibition of A94 was greater than A7 under the stress of different concentrations of Cd. The accumulation of Cd in whole A94 plant was more than that of A7, and the leaves were the main organ that could accumulate Cd. Furthermore, the activity of superoxide dismutase (SOD) in leaves and roots of A7 and A94 is significantly increased and hydrogen peroxide (CAT) and peroxidase (POD) activities were significantly reduced under the stress of Cd. Particularly, Salix psammophila 'Huangpi1' showed better Cd tolerence and had better ability of phytor emediation in Cd contaminated water.