The effects of organic fertilizer application on the soil microbial community in grassland systems have been extensively studied. However, the effects of organic fertilizers on the structure of rhizosphere microbial communities are still limited. In this study, the diversity and composition of rhizosphere microbial communities of a gramineous grass Elymus nutans under organic fertilizer treatment were studied in an artificial pasture on Qinghai–Tibet Plateau. After a growing season, the application of organic fertilizer not only increased the height and biomass of Elymus nutans, but also changed the rhizosphere microbial compositions. In particular, organic fertilizer increased the diversity of rhizosphere bacterial community and inhibited the growth of pathogenic bacteria such as Acinetobacter, but the opposite trend was observed for the diversity of fungal community. The assembly process of fungal community was changed from a stochastic process to a deterministic process, indicating that selection was strengthened. Additionally, both the infection rate of arbuscular mycorrhizal fungi (AMF) toward host plants and the development of AMF-related structures were significantly increased after the application of organic fertilizer. Our study demonstrated that the addition of organic fertilizer to artificial pasture could improve the growth of grass through the alteration of the rhizosphere microbial communities. Organic fertilizer had a greater selectivity for the bacterial and the fungal communities that enhanced the niche filtration in this community, further benefiting the yield of forages.

Chemical fertilizers are gradually being replaced with new biological fertilizers, which can improve the soil and soil microorganisms. In this experiment, leguminous forage (Medicago sativa cv. Beilin 201) was used as the research object. By measuring alfalfa root systems and soil properties and using high-throughput sequencing technology, we investigated the effect of biological (rhizobial) fertilizer at different concentrations on soil fertility and alfalfa rhizosphere microbiota in alpine grasslands. The results demonstrated that the treatment with biofertilizer significantly reduced total nitrogen (TN) and total organic carbon (TOC) content in soils, increased root densities, and significantly increased the number of root nodules in alfalfa. There were differences in the response of rhizosphere microorganisms to different concentrations of biofertilizer, and the treatment with biofertilizer led to pronounced changes in the microbial community structure. The abundance of beneficial bacteria such as Rhizobium, Arthrobacter, and Pseudomonas was significantly increased. The Pearson correlation analysis showed that soil moisture and soil conductivity were significantly positively correlated with the observed richness of rhizosphere microbiota (p < 0.05). Meanwhile, Actinobacteria showed a significantly positive correlation with nitrate, TOC, and TN (p < 0.01). These results indicated that biofertilizers enhanced soil fertility and altered the rhizosphere microbiota of alfalfa in alpine grassland.

The establishment of artificial grassland is crucial in restoring degraded grassland and resolving the forage–livestock conflict, and the application of organic fertilizer and complementary seeding of grass–legume mixture are effective methods to enhance grass growth in practice. However, its mechanism behind the underground is largely unclear. Here, by utilizing organic fertilizer in the alpine region of the Qinghai–Tibet Plateau, this study assessed the potential of grass–legume mixtures with and without the inoculation of Rhizobium for the restoration of degraded grassland. The results demonstrated that the application of organic fertilizer can increase the forage yield and soil nutrient contents of degraded grassland, and they were 0.59 times and 0.28 times higher than that of the control check (CK), respectively. The community composition and structure of soil bacteria and fungi were also changed by applying organic fertilizer. Based on this, the grass–legume mixture inoculated with Rhizobium can further increase the contribution of organic fertilizer to soil nutrients and thus enhance the restoration effects for degraded artificial grassland. Moreover, the application of organic fertilizer significantly increased the colonization of gramineous plant by native mycorrhizal fungi, which was ~1.5–2.0 times higher than CK. This study offers a basis for the application of organic fertilizer and grass–legume mixture in the ecological restoration of degraded grassland.

The biological mechanisms through which faba bean–oat intercropping coordinates interspecific competition, belowground responses, and system productivity remain poorly understood in alpine environments. A field experiment was conducted in the alpine region surrounding Qinghai Lake, with six treatments comprising faba bean monoculture (F), oat monoculture (O), and four faba bean–oat intercropping patterns with row ratios of 1:1 (FO), 2:1 (F2O), 2:2 (F2O2), and 1:2 (FO2). Agronomic traits, root morphology, soil physicochemical properties, and rhizosphere bacterial communities were measured to clarify above- and below-ground coordinated responses of the two crops to varying row ratios. The 2:1 faba bean–oat intercropping yielded the optimal performance, with a land equivalent ratio of 1.479 and a 29.3% higher dry matter yield (6795.4 kg ha⁻¹) than faba bean monoculture, as well as the highest system crude protein production. Dominant oat compensatory growth primarily boosted system productivity. Compared with the corresponding monocultures, the 2:1 intercropping treatment increased the total root length, root surface area, and root tip number of faba bean by 23.9%, 33.9%, and 54.3%, respectively, while increasing the total root length of oat by 110.3%. Under this treatment, soil alkali-hydrolyzable nitrogen reached 167.17 mg kg⁻¹, 39.9% higher than that under oat monoculture, whereas soil available phosphorus and catalase activity increased by 13.2% and 54.4%, respectively. Rhizosphere bacterial communities exhibited host-specific responses, with stronger treatment-associated differentiation in the oat rhizosphere and enrichment of Bacteroidia, Chitinophagales, and Chitinophagaceae under F2O. Partial least squares path modeling (PLS-PM) further revealed crop-specific pathways linking row configuration, belowground properties, bacterial α-diversity, and crop performance. Collectively, these findings demonstrate that the productivity advantage of faba bean–oat intercropping at a 2:1 row ratio is jointly mediated by competitive compensation of oat, enhanced root proliferation, improved soil nitrogen and phosphorus availability, and restructuring of rhizosphere bacterial communities.