Deficiency or excess of nitrogen (N) supply can promote formation of reactive oxygen species in plants, inducing oxidative stress. Otherwise, plants may enhance phenolics biosynthesis and antioxidant capacity under N deficiency, but this effect is plant species-dependent. There is no information about influence on phenolics and antioxidant activity in highbush blueberry (Vaccinium corymbosum L.), in which quality and commercial importance depend on high phenolics concentration. We studied the effect of variable N supply (0 to 38 mM) on N uptake and antioxidant responses in two highbush blueberry cultivars (Legacy and Bluegold) hydroponically grown at the long-term. Nitrogen leaves concentration was enhanced for both cultivars at increasing N supply. Bluegold decreased CO 2 assimilation at 0 N treatment, possibly due to both, insufficient N concentration and a decline in superoxide dismutase (SOD) activity. In contrast, SOD was activated in Legacy at 0 N, and interestingly only this cultivar maintained CO 2 assimilation rates across all N treatments. Both cultivars showed higher phenolics and antioxidant activity levels at 9 mM. Despite the differential responses among the cultivars, we propose a threshold of 15 g N kg-1 DW to ensure high antioxidant activity and quality in blueberry leaves.

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E. Yañez-Mansilla, P. Cartes, M. Reyes-Díaz, A. Ribera-Fonseca, and M. Alberdi. 2014. Photosynthetic and antioxidant performance are differentially affected by short-term nitrogen supply in highbush blueberry cultivars. Cien. Inv. Agr. 41(1): 61-70. Nitrogen (N) is an essential nutrient for photosynthesis and may influence phenolic compound synthesis in higher plants. The effect of different amounts of N (0 to 38 mM) provided on a short-term (4 d) basis on the photosynthetic and antioxidant performance of highbush blueberry cultivars (Legacy and Bluegold) grown in a nutrient solution was studied. In both cultivars, the N concentration of leaves slightly increased in response to the N supply, with Bluegold frequently showing higher N concentrations than Legacy. Photosynthesis was reduced in Bluegold at the highest N dose, whereas in Legacy, a decrease of CO 2 assimilation occurred under N starvation. This decrease in photosynthesis was accompanied by enhanced lipid peroxidation but only in Bluegold. In both cultivars superoxide dismutase (SOD) was activated with an increasing N supply. Legacy also showed increased SOD activity to counteract oxidative stress at higher N levels. Radical scavenging activity was not affected by the N supply. However, the total phenols and anthocyanins steadily declined in the leaves of Legacy, and flavonoids were significantly increased in the roots of both cultivars with increasing N treatments. Thus, our findings indicate that blueberry cultivars exhibit differential sensitivity to short-term N stress, and SOD appears to be more involved than phenolic compounds in the amelioration of N-induced oxidative stress. Further studies are required to confirm the sensitivity to either N starvation in Legacy or N excess in Bluegold under long-term conditions.