The Effects Of Ratio Of Nitrogen To Phosphorus Application On Interaction Of AMF-Wheat-Aphid

Chemical fertilizers and pesticides are critical for improvement of crop yield.However,abuse of fertilizers and pesticides could aggravate environmental pollution and pose threat to soil health.Understanding the effects of chemical fertilizers on the interactions of crops,pests and arbuscular mycorrhizal fungi(AMF)is important for reducing the applications chemical of fertilizers and pesticides,because AMF as a common symbiotic microorganism in terrestrial plants,can promote crop growth and improve resistance to pest insects.AMF colonization is known to be affected by the concentration of phosphorus in soil,less phosphorus improves its colonization.Meanwhile,the increase of AMF colonization rate can improve the nitrogen resorption efficiency and save nitrogen resource.In this study,we examined the effects of different concentrations of phosphorus and nitrogen(low,medium,high)on wheat growth,AMF,and wheat aphids,Sitobion avenae and Rhopalosiphum padi.We aimed to explore a best combination of phosphorus and nitrogen which would increase the AMF colonization rate,enhance the wheat yield and quality and the plant resistance to aphids,as well as reduce the application of pesticides.The results are as followed: 1.The effects of nitrogen and phosphorus on AMF colonizationThe AMF colonization rate on wheat root was increased significantly when plants were treated with low phosphorus content in nitrogen-phosphorus combination.The optimal combination of nitrogen and phosphorus was at low ratio of phosphorus and medium nitrogen or higher nitrogen,which increased the AMF colonization rate by 50% comparing to medium phosphorus and medium nitrogen in the combination.2.The effects of nitrogen andphosphorus on wheat growthIn the commom-garden test,the aboveground biomass and height of wheat plant treated with low phosphorus and medium nitrogen were significantly higher than those treated with medium nitrogen and medium phosphorus.The application with medium phosphorus and low nitrogen increased the belowground mass significantly,but the belowground mass was decreased when treated with high nitrogen.In the field tests,there was no significant difference between the treatment with low phosphorus and medium nitrogen and treatment with medium nitrogen and medium phosphorus.However,the belowground mass was higher than those of in low nitrogen treatments significantly,and there was no difference in teatments with high nitrogen.Treatment with low phosphorus and medium nitrogen or treatment with medium phosphorus and high nitrogen increased the number of wheat tillers significantly,but treatment high phosphorus inhibited the number of wheat tiller.However,the number of wheat tiller was decreased in high phosphorus content treatments.The yield did not increase when applied with high nitrogen,but it was positive correlated with AMF significantly.3.The effects of nitrogen and phosphorus on wheat aphidsRegardlesss of phosphorus content,the number of Sitobion avenae increased in high nitrogen content treatment,and the number decreased in the treatment with low nitrogen and medium phosphorus.The number of Rhopalosiphum padi increased with increase of nitrogen and phosphorus.Meanwhile,increasing nitrogen and decreasing phosphorus increased the number of alate aphid.There was negative correlation between AMF colonization and Sitobion avenae,but no relationship between AMF and the number of R.padi in the treatment with low phosphorus and low nitrogen.4.The effects of ratios of different nitrogen-phosphorus on metabolites of wheat plantsThere was no significant difference of total soluble sugar among all treatments.But the concentration of total phenol and flavonoids were increased in the treatment of low phosphorus and medium nitrogen: they were higher than those of in treatment of medium phosphorus and medium nitrogen by 1.3 times and 30% respectively.In treatment with low phosphorus and medium nitrogen,the correlation between AMF and total phenols and total flavonoids was positive significantly.Based on the above results,we concluded that there were different effects of different combination of nitrogen and phosphorus on wheat growth and yield.The treatment of low phosphorus and mediaum nitrogen was the best combination while there was higher AMF colonization rate that could increase the wheat growth and yield,and increase the resistance to aphids.