Effect of nitrogen fertilization and herbivory on pea plants and the preference of the aphid Acyrthosiphon pisum

The pea (Pisum sativum L.) is one of the most significant legumes in the world. This species is rich in proteins, vitamins, minerals and bioactive compounds that benefit human health. Although the symbiosis between atmospheric nitrogen-fixing bacteria (Rhizobium) and legume plants is well known, farmers apply nitrogen fertilizers to pea crops. It should be noted that imbalances due to excess nitrogen in plants cause population increases of insect pests. The aim of the study was to evaluate the effect of three levels of nitrogen [(N0= unfertilized, 0 Kg N ha^-1), (N1= medium level, 30 Kg N ha^-1), (N2= High level, 60 Kg N ha^-1)] and two infestation status (control and herbivory) on pea plants (dry weight) and its influence on the aphid Acyrthosiphon pisum. Our results indicate that high levels of nitrogen significantly increased the biomass of the aerial parts and its pods, unlike to others. However, root nodule biomass decreased significantly by increasing nitrogen. On the other hand, the aphid population was higher in plants at medium nitrogen level, in contrast to the rest. Whereas, A. pisum was mainly attracted to leaflets from plants over-fertilized (N2). Thus, the excess of nitrogen promoted the growth of pea plants, increasing the attraction and reproduction of the aphid A. pisum, due to the greater availability of food. However, the Rhizobium–legume interaction was inhibited by nitrogen applied. Therefore, further studies of the effect of inorganic nitrogen fertilization on symbiotic bacteria and plant defenses are required, to develop suitable minimum fertilization programs for crops, avoiding the loss of inputs, increases in pest populations, and inhibition of growth-promoting microorganisms, within the context of clean and sustainable agriculture.