Effects of continuous cucumber cropping on crop quality and soil fungal community.

Long-term continuous cropping is a common practice in facility vegetable production, which has an adverse effect on cucumber yield and quality. Soil fungi are of great significance for creating a normal soil ecological environment. However, the impact of continuous cropping on cucumber quality and soil fungal community has yet to be understood. In this study, we evaluated the effects of continuous cropping on cucumber using high-throughput sequencing technology. The results showed that the extension of continuous cropping would increase nitrate and total acidity of cucumber, while the contents of vitamin C (VC), soluble sugar, and protein were decreased. The increase of continuous cropping duration also reduced the fungal diversity of the cucumber soil. For example, the activity of three dominant fungal phylums, Ascomycota, Aphelidiomycota, and Basidiomycota, decreased with the extension of planting years. The relative abundance of the two fungi species (Remersonia_thermophila, Mortierella_oligospora) was negatively correlated with the contents of available phosphorus and available potassium (P < 0.05). Redundancy analysis (RDA) found that soil electrical conductivity (EC), available phosphorus (AP), and pH accounted for the top three major factors of fungal community structure changes. The soil fungal community was changed during the continuous cucumber cultivation, which might be the result of the combined cultivation period of cucumber and excessive application of chemical fertilizers (nitrogen fertilizer, phosphate fertilizer, etc.). Our study provides a theoretical basis for the understanding of the impact of continuous cropping in cucumber facilities.

Effects of exogenous sulfur on maize (Zea mays L.) growth and Cd accumulation in Cd-contaminated plastic shed soil.

Cadmium (Cd) pollution in plastic shed soils has become increasingly severe, posing a great threat to human health and social stability. Phytoremediation of cadmium pollution is an environmentally friendly and inexpensive remediation method. In this study, maize (Zea mays L.) was selected as the phytoremediation crop by a potted method, and the bioavailability of cadmium was investigated by adding exogenous elemental sulfur. The relationships among the sulfur content, maize growth, cadmium accumulation, and soil parameters were systematically studied. The results showed that, with the supplement of sulfur, the soil pH and activities of soil enzymes (urease, catalase, and sucrase) decreased gradually, and the available heavy metals (Cd, Cr, Zn, and Cu) in soil showed an upward trend. The optimal cadmium enrichment was achieved under T2 by increasing both the biomass of the maize plant and the cadmium concentration in roots and stems. However, T3 and T4 significantly inhibited the growth of maize roots and shoots, leading to a much lower plant biomass compared with that of CK (sulfur-free treatment) and T2. In addition, the cumulative cadmium was not increased because of the low accumulation of cadmium in some parts of the plant. Correlation analyses showed that the sulfur content was negatively correlated with soil pH and maize biomass (P < 0.01), and the cadmium content of whole maize was positively correlated with the dry weight of maize (P < 0.05) and the cadmium content in roots and stems (P < 0.01). In summary, to optimize cadmium phytoremediation of the plastic shed soil, an appropriate concentration of sulfur should be selected in practical applications to ensure that the biomass of the maize is maximized, and the cadmium concentration in different parts of the maize is increased or stabilized.