Cover crops are key determinants of the ecological stability and sustainability of continuous cropping soils. However, their agro-ecological role in differentially reshaping the microbiome structure and functioning under a degraded agroecosystem remains poorly investigated. Therefore, structural and metabolic changes in soil bacterial community composition in response to diverse plant species were assessed. Winter catch leafy vegetables crops were introduced as cover plants in a cucumber-fallow period. The results indicate that cover crop diversification promoted beneficial changes in soil chemical and biological attributes, which increased crop yields in a cucumber double-cropping system. Illumina high-throughput sequencing of 16S rRNA genes indicated that the bacterial community composition and diversity changed through changes in the soil properties. Principal component analysis (PCA) coupled with non-metric multidimensional scaling (NMDS) analysis reveals that the cover planting shaped the soil microbiome more than the fallow planting (FC). Among different cropping systems, spinach–cucumber (SC) and non-heading Chinese cabbage–cucumber (NCCC) planting systems greatly induced higher soil nutrient function, biological activity, and bacterial diversity, thus resulting in higher cucumber yield. Quantitative analysis of linear discriminant analysis effect size (LEfSe) indicated that Proteobacteria, Actinobacteria, Bacteroidetes, and Acidobacteria were the potentially functional and active soil microbial taxa. Rhizospheres of NCCC, leaf lettuce–cucumber (LLC), coriander–cucumber (CC), and SC planting systems created hotspots for metabolic capabilities of abundant functional genes, compared to FC. In addition, the predictive metabolic characteristics (metabolism and detoxification) associated with host–plant symbiosis could be an important ecological signal that provides direct evidence of mediation of soil structure stability. Interestingly, the plant density of non–heading Chinese cabbage and spinach species was capable of reducing the adverse effect of arsenic (As) accumulation by increasing the function of the arsenate reductase pathway. Redundancy analysis (RDA) indicated that the relative abundance of the core microbiome can be directly and indirectly influenced by certain environmental determinants. These short-term findings stress the importance of studying cover cropping systems as an efficient biological tool to protect the ecological environment. Therefore, we can speculate that leafy crop diversification is socially acceptable, economically justifiable, and ecologically adaptable to meet the urgent demand for intensive cropping systems to promote positive feedback between crop–soil sustainable intensification.

Garlic has a strong ability of selenium (Se) accumulation and is one of the best target crops for Se biofortification. Arbuscular mycorrhizal fungi (AMF) inoculation might enhance the nutritional qualities and the absorption ability of exogenous Se in plants. However, little is known about the exogenous Se application and AMF inoculation on garlic. Here, we evaluated the effects of different concentrations of exogenous Se on the growth, nutritional quality, and selenium enrichment of garlic. The results demonstrated that significantly higher Se content of garlic bulb was found in exogenous Se treated plants, and the Se accumulation was improved with the increasing of Se supply. Low application of exogenous Se appreciably improved the yield and the contents of soluble sugar and allicin in garlic bulbs, but the opposite was observed at high Se concentration. Furthermore, AMF inoculation significantly reduced the inhibition effect of high concentration Se on garlic. AMF supply was effective in improving the growth and nutritional indicators of garlic, which promoted the exogenous Se utilization rate when combined with 10 mg/L exogenous Se treatment. The results will provide a more theoretical basis for the production of high-quality selenium enrichment garlic.

Fruit shape and size are important assessment parameters to evaluate and classify accessions in cucumber breeding. Clarifying the relations of the shape and size of commodity fruits or mature fruits to that of other organs, like seed, leaf, flower and so on, is significant for multitype breeding of cucumber fruit. It can help breeders to predict the shape and size of a cucumber fruit in the early selection and shorten the breeding cycle. In this study, the dynamic morphological observation of fruit length (FL), fruit diameter (FD) and the fruit shape index (FSI) of developing cucumber fruits in different types and the correlation of fruit shape indexes between fruit and other organs were investigated. The results showed that 28 cucumber accessions with different shape and size were classified into four types, namely long fruits, medium long fruits, medium fruits and short fruits. The comparative analysis of FL and FD among different types and different development stages of cucumber fruits showed that the development of FL and FD were both consistent with the model “S” curve, slow–fast–slow, and there existed strong positive correlation between their growth. During fruit development, the shape index was highly positively correlated among ovary, commodity fruit and mature fruit. Besides, both the length and width of cotyledon, true leaf and female flower petal were positively correlated to the FL of commodity fruit. The length and width of seed, length of ovary carpopodium and pedicel length were also positively correlated to the FD of commodity fruit. For seed, cotyledon and true leaf, no correlation was found between their shape index and their FSI.