| Agriecosystems are dynamic systems experiencing the frequent chemical fertilizer inputs and change in plant species.So far,extensive fertilization in agriculture has reduced soil organic matter,exacerbated nutrient losses,and destroied the structure and function of soil communities,especially inhibiting the development of beneficial microorganisms associated with crop growth.However,appropriate and balanced chemical fertilizer inputs can improve soil biological function,and thereby promoting soil health.Therefore,there are some practices improving soil biological function and soil health,.Cover crops have been shown to increase soil organic matterand nutrient retention,enhance crop nutrient use efficiency,as well as promote soil biodiversity and function,and thereby improving the stability of agriecosystems.Therefore,the cereal crop-cover crop rotation has been considered to be a sustainable agricultural practice that can steer soil organisms to promote nutrient cycling and crop growth.However,so far,there is still a lack of knowledge regarding how nitrogen(N)fertilizers interacter with phosphorus(P)fertilizers to influence soil beneficial microbial community in this rotation system,especially the lack of research on the effects of the beneficial microorganisms and N and P retention affected by cover crop on cereal crop.To explore how N interact with P fertilizer inputs to influence soil biota commutity,and especially the effects of beneficial microorganisms,soil organic carbon and nutrient return affected by the green manure stage on nutrient uptake and yield of crop crops,we performed a factorial experiment with four N input leves(0,120,240,360 kg N ha-1)and two P input levels(0 and 90 kg P2O5 ha-1),conducted in a Summer maize-Winter green manure(Vicia villosa Roth)rotation system.Plants and soil were sampled to measure plant nutrient uptakes,biomass and grain yield soil as well as chemical properties including pH,soil organic carbon,mineral N,and total P for three seasons of maize(including two green manure plantings and incorporation),importantly,arbuscular mycorrhizal fungi(AMF)and nitrogen-fixing bacteria were selected as representatives of beneficial plant microorganisms.Results as followes:(1)N and P inputs significantly impacted the mycorrhizal colonization rate,and N interacted with P to affect the OTU numbers of AMF,and both depend on the sampling time.P inputs only reduced the mycorrhizal colonization rate of the maize under N360 in the second year of study,It may be that the interaction between phosphorus and high nitrogen fertilizers in the soil pH decreases and the high nitrate nitrogen content forms a strong interaction..However,the mycorrhizal colonization rate of maize decreases across N input gradients in the third year of study.Regardless of the sampling time,the numbers of AMF decreased with increasing N inputs under no P inputs,When P inputs,the N240 significantly increased the OTU numbers in the second year of study.However,N inputs had no significant effect on it in the third year of study.This is related to the buffer effect formed by the change of the nitrogen-fixing bacteria diversity under the influence of N input and the increase of the relative abundance of Glomus of AMF in the green manure season.(2)N and P inputs significantly affected the OTU number of nitrogen-fixing bacteria(p<0.05),and N interacted with P to affect the shannon diversity of nitrogen-fixing bacteria(p<0.05).In the maize season in the third year of study,N360 significantly reduced the shannon diversity of nitrogen-fixing bacteria compared with NO under no P inputs,however,Fertilizer inputs had no significant effect on it under P inputs.Correlation analysis showed that the change of nitrogen-fixing bacteria diversity was related to the decrease of soil pH in the maize season in two years.(3)The network complexity increased and then decreased with increasing N inputs under P0 in the second year of study especially the network complexity was highest under N240 condition.But it gradually decreased with increasing N inputs under P inputs.The positive interaction between AMF and nitrogen-fixing bacteria community enhanced.In the third year of study,the network complexity decreased with increasing N inputs under P0,modularity index increased,the positive interaction between AMF and nitrogen-fixing bacteria community gradually decreasing.The network complexity gradually decreased with increasing N inputs under P inputs.But positive interaction between AMF and nitrogen-fixing bacteria community strengthened.(4)Whether or not P input,maize grain yield showed an increasing tendency with increasing N inputs in the second year of study,while it tended to increase and then reduce with increasing N inputs in 2019,especially,it was highest under N120.In both years,N use efficiency decreased with incresing N inputs under P inputs conditions,it was highest under N120.Correlation analysis shows that this is mainly related to higher soil pH,lower mineral nitrogen content,and higher colonization rate and diversity of arbuscular mycorrhizal fungi at low N.The N uptake of shoot and roots increased with increasing N inputs in both years.The increase in N uptake of shoot is closely related to the increase C:N ratio in the green manure caused by N input and the decrease in the amount of N returned.(5)The structural equation model shows that the direct effects of N input and the effects of soil properties,beneficial microbial diversity and green manure growth in the green manure season indirectly affect the soil pH,mineral nitrogen content in the maize season,further affecting the diversity of AMF,which affects the NUE of maize.The application of nitrogen fertilizer directly and indirectly improves the N uptake of maize by changing the soil properties of green manure season,beneficial microbial diversity and green manure growth.In conclusion,Our study shows that the amount and interaction of nitrogen and phosphorus are strongly buffered by green manure.By measuring the growth of green manure and soil properties,it is helpful to understand the effect mechanism of N and P input on nutrient uptake of main crops and beneficial microbial communities after planting green manure.Moreover this study provided a theoretical basis for the formulation of weight loss management measures under the crop-green manure rotation system. |
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