To investigate the effect of fertilization on the rhizosphere microorganisms of the barley-pea mixed cropping system in the Sanjiangyuan region， this study took barley （Avena sativa） and forage pea （Pisum sativum） as the research objects. A randomized block experiment including nitrogen application （A₁）， phosphorus application （A₂）， nitrogen-phosphorus combined application （A₃）， and no fertilization （CK） was set up. Soil nutrients and root morphology were measured at the milk stage， and microbial communities were analyzed using high-throughput sequencing. The results showed that under the A₂ treatment， the ratio of root volume to rhizobacteria was 11.15% and 9.49% higher than that under the CK treatment （P<0.05）； under the A₃ treatment， the root surface area was 63.37% higher than that under the CK treatment （P<0.05）. The Venn diagram results indicated that the number of soil fungi under the A₁ treatment significantly increased， accounting for 28.89%， compared to 19.12% under the CK treatment； the α diversity index and β diversity index of the A₂ treatment indicated that phosphorus fertilizer significantly increased the number of fungi in the soil， and the ecosystem tended to be stable； the fungal functional group prediction results showed that after adding nitrogen and phosphorus， the structure and quantity of soil fungi shifted towards saprophytic type. In conclusion， nitrogen and phosphorus fertilization improved the root morphology parameters and soil microbial quantity and structure， and phosphorus fertilizer was more conducive to optimizing the root morphology and microbial community structure of the artificial grassland in the Sanjiangyuan region.

The Sanjiangyuan region  /  Addition of exogenous fertilizers  /  Artificial grassland  /  Mixed sowing of legumes and grasses  /  Root system ecosystem