Ultraviolet-B radiation (UV-B: 280-315 nm) has damaging effects on cellular components and macromolecules. In plants, natural levels of UV-B can reduce leaf area expansion and growth, which can lead to reduced productivity and yield. UV-B can also have important effects on herbivorous insects. Owing to the successful implementation of the Montreal Protocol, current models predict that clear-sky levels of UV-B radiation will decline during this century in response to ozone recovery. However, because of climate change and changes in land use practices, future trends in UV doses are difficult to predict. In the experiments reported here, we used an exclusion approach to study the effects of solar UV-B radiation on soybean crops, which are extensively grown in many areas of the world that may be affected by future variations in UV-B radiation. In a first experiment, performed under normal management practices (which included chemical pest control), we found that natural levels of UV-B radiation reduced soybean yield. In a second experiment, where no pesticides were applied, we found that solar UV-B significantly reduced insect herbivory and, surprisingly, caused a concomitant increase in crop yield. Our data support the idea that UV-B effects on agroecosystems are the result of complex interactions involving multiple trophic levels. A better understanding of the mechanisms that mediate the anti-herbivore effect of UV-B radiation may be used to design crop varieties with improved adaptation to the cropping systems that are likely to prevail in the coming decades in response to agricultural intensification.

The objective of this work was to compare and characterize the response to nitrogen (N) supply of a textile and an oilseed cultivar of flax (Linum usitatissimum L.). The dynamics of growth, biomass partitioning, growth rates, and leaf area evolution and duration of the cultivars Omega (oilseed) and Diane (textile) were compared under three rates of N supply. Plants were grown in pots in the field with nil (N1), 2.5 (N2), and 5 g N per pot (N3); N2 and N3 doses were divided into five applications. Shoot biomass of N2 and N3 treatments was similar in both cultivars and significantly higher than in N1. Partitioning of biomass was unaffected by N treatment but showed contrasting patterns between cultivars. The oilseed cultivar produced 30 -42% more reproductive biomass and 18-30% less stem biomass than its textile counterpart. Differences between cultivars in these traits increased with increasing N rate. Maximum growth rates per plant concentrated around 15728Cd after sowing (fructification). Faster leaf senescence after flowering contributed to the lower leaf area and leaf biomass of the textile cultivar.The availability of N at different specific moments of the plant cycle would be useful to improve the growth of organs of economic interest. Results can also provide useful information to future nutrition models and breeding programs in textile and oilseed flax.