| Intercropping is widely used in agricultural production as a planting method to improve land use efficiency,which has the characteristics of increasing productivity and resource utilization efficiency.The yield and nutrient utilization advantages of intercropping systems have been extensively studied.However,the study on maize/soybean intercropping productivity,nutrient utilization efficiency and changes of soil and root microorganism diversity driven by interspecific interaction between crops under different nitrogen application rates,especially in the black soil area of Northeast China,has been rarely carried out.In the previous research,the study of two-year(2017-2018)field experiment mainly focused on contribution of complementarity and selection effects to productivity and nutrient obtain,and changes of microbial diversity in rhizosphere soil driven by interspecific interaction,especially the relationship between root AMF diversity and soil nutrient variation.The effects of nitrogen application on the productivity of maize/soybean intercropping system and the mechanism of efficient utilization of nutrient resources were studied systematically from above ground and underground,which provided reference value for reducing nitrogen application in intercropping system.The main results are as follows:(1)Grain yield of maize and soybean were both significantly affected by nitrogen(N)application,which had the highest yield under the N3(300 kg N ha-1)treatment.The grain yield of intercropping system under N0,N1(180 kg N ha-1),N2(240 kg N ha-1)and N3(300 kg N ha-1)treatments significantly increase by 25.26%,23.28%,22.65%and 12.71%compared with monoculture treatments.Under the four N application rates,LER of grain yield were both higher than 1,which indicated that intercropping had obviously productivity advantage with different N application.However,the LER was not significantly affected by N application rates.(2)Biomass of maize and soybean were significantly affected by the N application rates,which was different with the grain yield.In maturation stage,the LER of biomass in intercropping system was higher than 1 under the N0 treatment,which was lower than 1 under the other 3 treatments.LER of biomass in intercropping system was significantly affected by N application rates and decreased with the increase of N application.(3)The total N,P and K uptake of intercropping system were significantly affected by N application rates,which were highest at the N3 treatment.Compared with monoculture,the total N uptake in intercropping system increased by 10.42%,11.60%,13.81%and 10.02%respectively,under the 4 N treatments.The increase of intercropped relative to monoculture in N uptake was highest under the N2 treatments.The economic utilization efficiency of N uptake increased by 12.08%,18.70,20.05%and 16.21%respectively,under the 4 N application than monoculture,which of K were 19.67%,25.97%,29.94%and 26.54%respectively.The increase of intercropped relative to monoculture in N and K economic utilization efficiency were highest under N2 treatment,which in N and K biological yield utilization efficiency were highest under N3 treatment.The nutrient uptake and utilization efficiency of the intercropping system have different responses to cultivation method and N application rates.The nutrient uptake and difference of biological yield utilization efficiency between monoculture and intercropping are the largest under N3 treatment,while the difference of economic yield nutrient utilization efficiency between monoculture and intercropping is the largest in N2 treatment.(4)Productivity changes and nutrient uptake availability advantages of maize/soybean intercropping systems were driven by the complementarity and selection effects.The grain yield advantage in intercropping system was the result of positive complementarity and selection effects.However,the changes of biomass in the intercropping was mainly affected by the positive selection effect,which significantly increased with the increase of N application.The highest selection effect of biomass presented at the N2 treatment.In 2017,the contribution of complementarity effect to grain yield decreased with the increase of N application,but the contribution of selection effect to grain yield increased when N application increased.(5)The change of nitrogen uptake in intercropping system is the result of complementarity and selection effect.With the increase of N application rate,complementarity effect decreased,while selection effect increased.Both the complementarity and selection effect of N uptake reached their maximum values at N2 treatment,were 19.11 and 8.41,respectively.The change of P uptake in intercropping system is mainly due to the positive selection effect and the change of K uptake is the result of the combination of complementarity and selection effect.The selection effect of P and K uptake both reached the maximum under N2 treatment,which were 5.85 and 7.92 respectively.The contribution of complementarity and selection effect to different nutrient uptake of intercropping system was different.(6)N fertilization significantly decreased the AMF?diversity in maize rhizosphere soil and root,had no effect on the?diversity in soybean rhizosphere soil and root.Intercropping significantly increased the AMF?diversity of soybean rhizosphere soil,had no effect on the AMF?diversity in maize rhizosphere soil and root.On genus lever,Glomus?f?Glomeraceae was the dominant genera in maize rhizosphere soil and root,which had the highest relative abundance.Contrary to root AMF diversity,the relative abundance of Glomus?f?Glomeraceae in maize root significantly increased with the increase of N application rates.The results of Mental test showed that,AMF community structure in maize rhizosphere soil and root were significantly correlated with TN(p=0.037?p=0.006)and AN(p=0.001?p=0.001)content in rhizosphere soil,which in soybean root was significantly related to soil OM(p=0.031),AN(p=0.032)and N:P ratio(p=0.044).The interspecific interaction between maize and soybean significantly decreased the AN content of soybean rhizosphere soil,which resulting in a significant increase in AMF diversity of soybean rhizosphere soil.(7)Intercropping significantly decreased the AOA and AOB?diversity of maize rhizosphere soil,but significantly increased the AOA?diversity of soybean rhizosphere soil.When the N application rates increased,the AOB?diversity of soybean rhizosphere soil increased significantly,which was higher in N2 treatments compared with that in N0 and N1 treatments.The relative abundance of Nitrososphaera in the rhizosphere soil of maize and soybean was significantly affected by N application and increased with the increase of N application.The results of Mental test showed that,the AOA community structure of soybean rhizosphere soil was significantly correlated with the content of soil AN(p=0.050).The?diversity of AOA in soybean rhizosphere was significantly higher than that of monoculture due to the decrease of AN content in soybean rhizosphere soil caused by intercropping.The dominant genera Nitrosospira of AOB in the rhizosphere soil of maize and soybean were significantly affected by N application rate on genus level,and increased with the increase of N application.The relative abundance of Nitrosospira was significantly affected by intercropping,which were significant higher in intercropped maize and soybean rhizosphere than that in monoculture.The results of Mental test showed that,community structure of AOB in maize rhizosphere soil was significantly related to content of soil TN(p=0.021)and AN(p=0.001).Because of interspecific interaction in intercropping system,the content of TN and AN in rhizosphere soil of maize was significantly higher than that of monoculture,which resulted in the decrease of AOB diversity of intercropping treatment,and the increase of relative abundance of dominant genera.(8)Through the comprehensive analysis of structural equation model,nitrogen application had direct positive effects on rhizosphere soil nutrient,mycorrhizal colonization rate,rhizosphere soil and root AMF community structure,and direct negative effects on rhizosphere soil AOA and AOB community structure.Intercropping had significant effects on microorganism diversity and community structure in rhizosphere soil,and intercropping and rhizosphere soil AMF community structure had direct and significant effects on mycorrhizal colonization rate(p<0.05).Rhizosphere soil nutrients and AMF community structure have direct and significant effects on rhizosphere soil AOB community structure(p<0.05).The community structure of rhizosphere soil AMF and mycorrhizal colonization rate had direct positive effects on rhizosphere soil AOB community structure and negative effects on rhizosphere soil AOA community structure,the community structure of rhizosphere soil AOA had direct negative effects on rhizosphere soil AOA community structure.Maize/soybean intercropping has obvious productivity and nutrient absorption advantages.Through the analysis of complementarity and selection effects,which had been found that nitrogen application can regulate the interaction between crops.Soil nutrient changes caused by interspecific interaction affect the diversity and community structure of soil AMF?AOA and AOB,and the interaction between these microorganisms also affects each other's community structure. |
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