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Item The inhibition of N 2 fixation by nitrogen is attenuated by the P supply, altering the plant metabolismAutores: Cabeza, Ricardo A.; Schulze, Joachim; Salinas Roco, Sebastián; Morales González, Amanda; Amigo, Ramón; Pérez Díaz, Ricardo; Carrasco, Basilio; Contreras Soto, Rodrigo; Maldonado, Carlos; Pedreschi, Romina; Espinoza, Soledad; del Pozo, AlejandroSoil nitrogen (N) acts as an inhibitor to the biological process of N 2 fixation in legumes. Conversely, the phosphorus (P) supply fosters N 2 fixation by promoting nodule formation, facilitating energy transfer, activating enzymes, and enhancing nitrogenase activity. This could help counteract the inhibitory effects that high soil N levels can have on N 2 fixation in legumes. However, there is limited knowledge regarding whether P supply can mitigate the inhibition of N 2 fixation. The objective of this work was to evaluate the effects of two levels of P and five N levels on N 2 fixation, shoot, root, and nodule biomass produced, and metabolic changes of leaves and nodules of Pisum sativum and Vicia faba . N 2 fixation was determined by measuring the natural abundance of 15 N (%Ndfa) in shoots and roots, and metabolites were evaluated using GC -MS. The results showed that increasing N levels led to a reduction of N 2 fixation at the two P levels in both species. However, P supply reduced the inhibitory effect of N addition on N 2 fixation due to higher plant biomass production, which resulted in an increased mass of nodules. Under P deficiency, N addition affected N 2 fixation due to energy production in the nodules, which led to the accumulation of sugars and organic acids, especially in P. sativum . The response of N 2 fixation to a high N supply indicates that P. sativum and V. faba downregulated N 2 fixation but maintained viable nodules to resume the process if the N supply in the soil decreases.Item N2 Fixation, N Transfer, and Land Equivalent Ratio (LER) in Grain Legume-Wheat Intercropping: Impact of N Supply and Plant DensityAutores: Salinas Roco, Sebastián Alberto; Morales González, Amanda Belén; Espinoza, Soledad; Pérez Díaz, Ricardo; Carrasco, Basilio; del Pozo Lira, Alejandro Humberto; Cabeza Pérez, Ricardo AlfonsoIntercropping legumes with cereals can lead to increased overall yield and optimize the utilization of resources such as water and nutrients, thus enhancing agricultural efficiency. Legumes possess the unique ability to acquire nitrogen (N) through both N-2 fixation and from the available N in the soil. However, soil N can diminish the N-2 fixation capacity of legumes. It is postulated that in intercropping, legumes uptake N mainly through N-2 fixation, leaving more soil N available for cereals. The latter, in turn, has larger root systems, allowing it to explore greater soil volume and absorb more N, mitigating its adverse effects on N-2 fixation in legumes. The goal of this study was to evaluate how the supply of N affects the intercropping of faba beans (Vicia faba L.) and peas (Pisum sativum L.) with wheat under varying plant densities and N levels. We measured photosynthetic traits, biomass production, the proportion of N derived from air (%Ndfa) in the shoot of the legumes, the N transferred to the wheat, and the land equivalent ratio (LER). The results revealed a positive correlation between soil N levels and the CO2 assimilation rate (An), chlorophyll content, and N balance index (NBI) in wheat. However, no significant effect was observed in legumes as soil N levels increased. Transpiration (E) increased in wheat intercropped with legumes, while stomatal conductance (g(s)) increased with N addition in all crops. Water use efficiency (WUE) decreased in faba beans intercropped with wheat as N increased, but it showed no significant change in wheat or peas. The shoot dry matter of wheat increased with the addition of N; however, the two legume species showed no significant changes. N addition reduced the %Ndfa of both legume species, especially in monoculture, with peas being more sensitive than faba beans. The intercropping of wheat alleviated N-2 fixation inhibition, especially at high wheat density and increased N transfer to wheat, particularly with peas. The LER was higher in the intercropping treatments, especially under limited N conditions. It is concluded that in the intercropping of wheat with legumes, the N-2 fixation inhibition caused by soil N is effectively reduced, as well as there being a significant N transfer from the legume to the wheat, with both process contributing to increase LER.
