4.2. Nitrogen EffectsNitrogen fertilisation had much less effect on organ nutrient concentration than on the amount of nutrients acquired by above-ground organs reflecting a higher influence of N on plant biomass production. Nonetheless, the decrease of the concentrations of some elements in specific plant organs of N-starved plants was evident, namely, those of N, Ca, Cu, and thoroughly Mn, although only the N concentration was out of the desired nutrient concentration ranges for maize. This result had significant effects on maize physiology, mainly on carbon metabolism [12], since a greater part of N concentration in leaves is associated with the chloroplasts.

The lower amount of nutrients acquired in N-stressed plants, as in other studies [35, 36], namely, for N after silking, indicates the need of decomposition and remobilization of nitrogen compounds accumulated before flowering, a significant fact since the reproductive stage is considered the critical period for N uptake in maize [37]. Furthermore, the continuous absorption of N allows the normal development of embryo, with positive implications on hormonal balance, and the maintenance of enzymatic systems involved in starch and proteins accumulation [38]. Nitrogen application affects maize grain quality. As in other studies [36, 39], N concentration and thus crude protein concentration were lower in N-stressed plants. Meanwhile, effects of N were not observed on grain concentration of the other elements, which corroborates the findings of Ahmadi et al. [40]. As expected [35, 36, 41], NUE was higher in N-starved plants, except at high UV-B, for the reasons reported before.

Nevertheless, it is possible that the lower NUE in high N doses was also related to higher N losses by NH3 volatilization, commonly associated with higher stomatal conductance [42].5. ConclusionsThe results of this study indicated the existence of interactive effects between UV-B AV-951 radiation and nitrogen treatments on nutrient concentration and on the amount of nutrients acquired by maize shoot. In order to minimize nutritional, economical, and environmental negative consequences, fertiliser recommendations for maize based on element concentration in crop shoots or yield goals may need to be adjusted. Moreover, UV-B sensitivity in vegetative organs and grain quality in addition to sensitivity in growth and yield may become important criteria for future plant breeding programs. Table 3Interactive effects of UV-B radiation and nitrogen on P concentration (mgg?1) and P acquired (gm?2) by above-ground organs of maize.Table 4Interactive effects of UV-B radiation and nitrogen on K concentration (mgg?1) and K acquired (gm?2) by above-ground organs of maize.