Biomass and nitrogen fixation dataset of Pisum sativum L. and Vicia faba L. cultivated under elevated CO2 and nitrogen addition.

It is expected that CO2 concentration will increase in the air, thereby stimulating the photosynthesis process and, hence, plant biomass production. In the case of legumes, increased biomass due to higher CO2 concentration can stimulate atmospheric nitrogen (N2) fixation in the nodules. However, N2 fixation is inhibited by external N supply. Thus, biomass production and N2 fixation were analysed in two legumes (Pisum sativum L. and Vicia faba L.) grown at two levels of CO2 and three N levels. P. sativum reduces fixation with high soil N (facultative), while V. faba maintains high fixation regardless of soil N levels (obligate). The N2 fixation and plant and nodule biomass of the two species were evaluated in a pot experiment under controlled conditions using growth chambers with artificial CO2 supply and N addition. The proportion of N derived from the air (%Ndfa) present in the plants' biomass was calculated from the natural abundance of 15N and the N concentration of plant tissues using nonlegumes reference plants. Additionally, N content data are presented for both species growing at two levels of air CO2. The data may be useful for plant physiologists, especially those working on biological N2 fixation with non-model legumes at elevated CO2.

N2 Fixation, N Transfer, and Land Equivalent Ratio (LER) in Grain Legume-Wheat Intercropping: Impact of N Supply and Plant Density.

Intercropping 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 N2 fixation and from the available N in the soil. However, soil N can diminish the N2 fixation capacity of legumes. It is postulated that in intercropping, legumes uptake N mainly through N2 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 N2 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 (gs) 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 N2 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 N2 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.