Intercropping can enable more efficient resource use and increase yield. Most current studies focus on the correlation between soil nutrients and crop yield under intercropping conditions. However, the mechanisms related to root exudates and soil nutrients remain unclear. Therefore, this study explored the correlation between rhizosphere soil nutrients and root exudates in sugarcane/peanut intercropping. Root extracts, root exudates, rhizosphere soil enzyme activities, and soil nutrients were analyzed and compared in monocultured and intercropped peanut and sugarcane at different growth stages. The root metabolites were annotated using the Kyoto Encyclopedia of Genes and Genomes pathways to further identify the connection between soil nutrients and root exudates. The effects of intercropping differed in peanut and sugarcane at different growth stages, and the difference between podding and pod-filling stages was significant. Intercropping generally had a great effect on peanut; it not only significantly increased the organic acid, soluble sugars, and phenolic acids in root exudates and extracts from peanuts, but also significantly increased rhizosphere soil enzyme activities and soil nutrient levels. Intercropping peanuts promoted fumaric acid secretion from roots and significantly affected the metabolic pathways of alanine, aspartate, and glutamate. Sugarcane/peanut intercropping can increase root exudates and effectively improve soil nutrients. The changes in soil nutrients are closely related to the effects of fumaric acid on alanine, aspartate, and glutamate metabolism.

The intercropping of peanuts and sugarcane is a sustainable planting model that deserves in-depth research. For this study, two variables, i.e., intercropping status (peanut monocropping or sugarcane/peanut intercropping) and the level of nitrogen fertilization (low, medium, or high), were evaluated to analyze the effects of intercropping and nitrogen application on soil fertility and microbial communities in peanut rhizosphere soil. These analyses revealed that higher nitrogen application led to increased total nitrogen (TN), available nitrogen (AN), and soil organic matter (OM) levels in rhizosphere soil for both monocropped and intercropped peanuts, with a decrease in pH. Monocropped peanuts had higher TN, total phosphorus (TP), and total potassium (TK) levels compared to intercropped peanuts at the same nitrogen level but lower AN content and pH levels. The diversity of microbial communities in the rhizosphere soil of intercropped peanuts was significantly higher than that of monocropped peanuts under high levels of nitrogen fertilizer application. Higher levels of Gemmatimonadetes abundance were observed in intercropping rhizosphere soil, compared to that associated with peanut monocropping under low, middle, and high levels of nitrogen fertilizer application, whereas the opposite trend was observed for Chloroflexi abundance. Nitrospira abundance levels rose gradually in the monocropping treatment group, whereas the opposite trend was evident under intercropping conditions. Further analyses of nitrogen cycle-related genes demonstrated higher levels of nitrogen conversion cycle activity in intercropping peanut rhizosphere soil under low nitrogen levels, whereas nitrogen transformation cycle activity levels were higher in monocropping peanut rhizosphere soil under high levels of nitrogen amendment. It can be concluded that intercropping and nitrogen fertilizer application change the physical and chemical properties of soil, thus affecting the diversity and function of soil microbial communities in the peanut rhizosphere. These results offer a theoretical foundation for more efficient sugarcane/peanut intercropping systems.

Wild peanut species Arachis correntina (A. correntina) had a higher continuous cropping tolerance than peanut cultivars, closely correlating with the regulatory effects of its root exudates on soil microorganisms. To reveal the resistance mechanism of A. correntina to pathogens, we adopted transcriptomic and metabolomics approaches to analyze differentially expressed genes (DEGs) and differentially expressed metabolites (DEMs) between A. correntina and peanut cultivar Guihua85 (GH85) under hydroponic conditions. Interaction experiments of peanut root exudates with Ralstonia solanacearum (R. solanacearum) and Fusarium moniliforme (F. moniliforme) were carried out in this study. The result of transcriptome and metabolomics association analysis showed that there were fewer up-regulated DEGs and DEMs in A. correntina compared with GH85, which were closely associated with the metabolism of amino acids and phenolic acids. Root exudates of GH85 had stronger effects on promoting the growth of R. solanacearum and F. moniliforme than those of A. correntina under 1 and 5 percent volume (1% and 5%) of root exudates treatments. Thirty percent volume (30%) of A. correntina and GH85 root exudates significantly inhibited the growth of two pathogens. The exogenous amino acids and phenolic acids influenced R. solanacearum and F. moniliforme showing concentration effects from growth promotion to inhibition as with the root exudates. In conclusion, the greater resilience of A. correntina) to changes in metabolic pathways for amino acids and phenolic acids might aid in the repression of pathogenic bacteria and fungi.