Effects Of Sowing Combination And Ratio On The Productivity Of Legume-grass Mixtures And Soil Microbial Community

The establishment of legume-grass mixture can effectively increase the yield and quality of forage and improve soil fertilization.However,due to the inappropriate mixed combination or ratio of plant species,legume-grass mixtures often suffer from poor forage growth,intense interspecific competition,and unstable community structure,resulting in insufficient productivity.In this experiment,four common plant species of legumes and grass,Dactylis glomerata,Lolium perenne,Trifolium repens,Trifolium pratense,were selected to build legume-grass mixtures at legume and grass sowing ratio at 4:6,3:7 and 5:5.The 3 cm and 30 cm soil layers were labeled by ¹⁵N stable isotopes,and the above-ground biomass,species diversity,¹⁵N uptake by different species,soil nutrient content,microbial carbon and nitrogen content,as well as microbial community diversity and community composition were determined for the legume-grass mixture.The main results are as follows:In 2020,neither the mixed combination nor the mixed ratio had significant effects on above-ground biomass.In 2021,the legume-grass mixture showed a significant overyielding effects,mostly caused by complementary effects.The productivity and species asynchrony in D.glomerata+L.perenne+T.repens+T.pratense mixtures were significantly greater than other mixed combinations and monocultures.However,the sowing ratios did not have significant effects on grassland productivity,community stability and species asynchrony.Compared to the monocultures,the legume-grass mixture increased the nitrogen tracer uptake of aboveground biomass.The nitrogen tracer uptake of aboveground biomass in D.glomerata+L.perenne+T.repens+T.pratense were 9 times and 10.5 times higher than that of monoculture T.repens and T.pratense respectively.D.glomerata and L.perenne mainly absorbed the nitrogen tracer from 3 cm soil layer,while the nitrogen fixation and nitrogen capture for T.repens and T.pratense occurred in both 3 cm and 30 cm soil layers.The L.perenne+T.repens+T.pratense mixture had the greatest soil bacterial richness and fungal diversity,while the greatest fungal richness was detected in the combination of D.glomerata+L.perenne+T.repens+T.pratense.For bacterial community,the relative abundance of acidobacteriota and verrucomicrobiota were significantly greater in the D.glomerata+L.perenne+T.repens+T.pratense mixtures than other mixtures.For fungal community,the relative abundance of ascomycetes in the D.glomerata+T.repens+T.pratense was significantly greater than other mixtures.Soil ammonium nitrogen and plant aboveground biomass were the main factors driving the soil bacterial community diversity,and the fungal community composition were most affected by plant total phosphorus,plant available phosphorus,microbial biomass carbon and nitrogen.In summary,the D.glomerata+L.perenne+T.repens+T.pratense had the greater aboveground productivity and stability,due to the multiple characteristics of 4 plant species for vertical nutrient capture and niche separation.Our results provided theoretical basis and technical support for the establishment of high productive legume-grass mixtures and ecological restoration of degraded grassland.