Photosynthetic and antioxidant performance are differentially affected by short-term nitrogen supply in highbush blueberry cultivars
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 CO2 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.