ObjectiveGreen manuring is considered to be an effective strategy to achieve sustainable development in agriculture. It plays key roles in ameliorating soil fertility, improving fruit quality, and enhancing resource use efficiency. China is the world's largest strawberry (Fragaria×ananassa Duch.) producer, with strawberry cultivation taking place mainly in greenhouses. However, many field management practices, such as long-term monoculture and irrational chemical fertilization, reduce the fruit yield and quality of strawberries. Therefore, it is important to investigate the effects and mechanisms of green manuring on strawberry yield and quality in greenhouses.MethodThree gramineous green manures, i.e., maize (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench], and sorghum-sudangrass (Sorghum×sudangrass), were selected to carry out a field experiment from 2017 to 2021. There were four treatments: fallow farmland-strawberry (control), maize-strawberry, sorghum-strawberry, and sorghum-sudangrass-strawberry. Samples were collected in the full fruit stage of strawberries to determine plant growth and physiological parameters, in addition to fruit yield and quality attributes. Rhizosphere soil chemical properties, bacterial community structure, and metabolome were also analyzed.ResultThe different green manure treatments promoted plant growth and yield formation, and improved the fruit quality of subsequent strawberry crops. The most prominent effects were observed for the corn green manure treatment, which increased strawberry plant dry weight, root growth, and leaf chlorophyll content (SPAD value) by 53.4%, 21.0% - 94.7%, and 7.8%, respectively, compared with the control treatment. Also, fruit yield per plant was markedly improved by 44.6% in the corn green manure treatment, along with the increase of nutrient contents (total sugar: by 13.9%; vitamin C: by 14.4%; and soluble solids: by 12.8%). Soil pH, cation exchange capacity, organic matter content, and nutrient availability (N, P and K) were also strongly increased under the corn green manure treatment, while sucrase, phosphatase, and urease activities were enhanced simultaneously. Green manuring mediated an increase in the diversity and abundance of rhizosphere soil bacterial communities, coupled with a distinct enrichment of potentially beneficial bacteria, such as Flavobacterium, Variovorax, and Pedobacter. The increase in the abundance of potentially beneficial bacteria might be related to a considerable increase in the relative abundance of carbohydrate metabolites (e.g., sorbose, mannose, and fructose) associated with green manuring. A remarkable decrease in the relative abundance of lipid metabolites (e.g., palmitic acid, stearic acid, and oleic acid) alleviated the autotoxicity of strawberries.ConclusionGramineous green manure-mediated shifts in specific metabolites in the rhizosphere soil improved strawberry yield and quality by recruiting potentially beneficial bacteria and alleviating allelopathic autotoxicity. Maize green manure is a better option compared to sorghum and sorghum-sudangrass green manures for greenhouse strawberry production.