Wheat-mediated Interactions Between Shoot-feeding Aphids And Cyst Nematodes Depend On Nitrate Fertilization

Fertilization is an important measure to increase grain yield.Nitrogen fertilizers can also have a negative impact on the ecosystem while increasing food production.Although increasing grain yield,at the same time nitrogen fertilizer has negative impact on the soil ecosystem.Excessive nitrogen fertilizer in farmland changes the sensitivity of crops to pests and diseases,influences other species,and changes interspecific relationships by bottom-up effect.Herbivores which feed on the plant select plant suitability by measuring different morphological and chemical cue.Herbivore feeding results in part and thorough changes in the composition of the plant secondary metabolites,and these changes have considerable effect on the performance of co-occurring or later arriving phytophages.Winter wheat(Triticum aestium)is regarded as the most important food crop in the world.Winter wheat aphids and cereal cyst nematodes are important pests on the ground and underground parts of winter wheat.Under the influence of different nitrogen fertilizers and herbivores,whether the changes in the metabolism of winter wheat alters the relationship between herbivores is still poorly understood.Two experiments included two levels of nitrogen fertilizer(FH:180kg/hm2,FL:60 kg/hm2)and two feeding on winter wheat herbivores.One experiment was set firstly to infect the aboveground aphids,and another experiment was done firstly to infect the belowground parasitic nematode.The relationship between wheat-mediated aphids and cyst nematodes was examined through the changes of primary and secondary metabolites in the plant growth process.The results enable us to better understand the relationship among winter wheat,aphids,and cyst nematodes,providing theoretical basis for rational application of nitrogen fertilizers and controlling pests,stability of grain yield,and protection of farmland environment.1?Effect of nitrogen fertilizer inoculation with nematodes on aphid.The nitrogen fertilizer was set two levels:high nitrogen(FH)and low nitrogen(FL).The herbivores included two species inoculation:The herbivores were treated with aphids and cyst nematodes(A+),aphids,and cyst nematodes(A+),for a total of four treatments.The results indicated:Aphid had no significant effect on the number of soil cysts(F=1.151,P=0.249),and nitrogen fertilizer had a significant effect onthe number of soil cysts(F=47.849,P<0.01).Low nitrogen fertilizers had no effect on cyst nematodes,but high nitrogen fertilizers inhibited growth of cyst nematodes.The above-ground and underground biomass of nitrogen-fertilized winter wheat(F=20.801,P<0.001,F=6.911,P=0.015).The negative effect of nitrogen fertilizer on total root length,root surface area and root volume of winter wheat(F=17.636,P<0.01 F=24.215,P<0.01,F=10.789,P<0.01)was significant,but there was no significant difference in root to crown ratio.The effect(F=2.204,P=0.151).Nitrogen fertilizer had significant total N content in stems and leaves and in roots(F=10.603,P<0.01;F=7.900,P=0.016),but total C content in stems and leaves and root system(F=2.057,P= 0.177;F=0.004,P=0.953)Not significant.Aphid to above ground,belowground biomass,total root length,root surface area,root volume(F=269.169,P<0.001;F=269.169,P<0.001;F=185.506,P<0.01;F=128.960,P<0.01;F=168.940,P<0.01).The effect was significant on soluble sugar content in stem and leaf(F=8.689,P=0.007)and total C content in root system(F=14.450,P<0.01).The interaction between nitrogen fertilizer and aphid significantly affected the total C content in stems and leaves of winter wheat(F=5.895,P=0.032).Among them,the number of cysts in the soil was significantly positively correlated with the total C content in the root system and C/N.2?The second experiment:the effect of the cyst nematode inoculation firstly on aphid.The nitrogen fertilizer was set two levels:high nitrogen(FH)and low nitrogen(FL).The herbivores included two species inoculation:with(A+)and without aphids(A-),with(N+)and without cyst nematode(N+).Selective experimental results showed that aphid preference was affected by nitrogen fertilizer and cyst nematode aphid preferred the plants without cyst nematode inoculation.The selection index of aphids was negatively correlated with soluble sugar content and total phenolic content in stems and leaves,and positively correlated with amino acid content.The effect of cyst nematode inoculation on aphid results indicated:The effect of nitrogen fertilizer on the number of aphids was significant(F=7.004,P=0.013).The effect of cyst nematode on the number of aphids was not significant(F=1.329,P=0.259).Nitrogen aboveground biomass of winter wheat,underground biomass(F=13.020,P<0.01),total N content in stems and leaves,and free amino acid content in leaves(F=5.843,P=0.026;F=40.493,P<0.01)The effect is significant.The underground biomass and root/shoot ratio of cyst nematode on winter wheat reduced the content of soluble sugar in stem and leaf,but the effect was not significant,and had a significant effect on the content of free amino acids in leaves(F=4.650,P=0.040).The results of regression analysis showed that the increase in the number of aphids was most strongly correlated with the soluble sugar,amino acid and total C content of winter wheat,and both were positively correlated.Conclusions:Aphids and cyst nematodes can affect each other through changes in plants,and aphids affect nematodes by altering the growth of wheat roots and the proportion of carbon and nitrogen in the plant.Cyst nematodes affect aphids by affecting the amount of primary and secondary metabolites in wheat.Nitrogen fertilizer can change the relationship between aphids and cyst nematodes by changing the growth and nutritional status of wheat.Aphids have no effect on cyst nematodes at low nitrogen levels,while cyst nematodes reduce the number of aphids;aphid energy at high nitrogen levels.The growth of cyst nematodes was inhibited,whereas cyst nematodes did not have a significant effect on aphids.