Boron (B) deficiency is a common micronutrient deficiency that has been reported to affect the phenolic metabolism of plants. Thus, it may play a role in defense against herbivorous animals. However, the role of B in a plant's resistance to herbivores has not received any particular attention from researchers. In this study, we tested the effects of B nutrition 1) on the biochemical and mechanical defenses of birches and the growth of seedlings, and 2) the resistance of seedlings to larvae of the autumnal moth, Epirrita autumnata. Boron fertilization improved the resistance of birch, which was shown as reduced pupal weight of the herbivore. However, B fertilized trees suffered from heavier defoliation than unfertilized ones due to compensation feeding of larvae. The growth of the seedlings was diminished, and several biochemical changes occurred in leaves of herbivore seedlings, and B also played a role in these changes. Polyphenoloxidases (PPOs) and peroxidases (PODs) and their substrates, chlorogenic acids, were induced by herbivory in B fertilized seedlings but not in unfertilized seedlings. The lower pupal weights and increased consumption of the herbivores were probably linked to the plants' phenoloxidase-mediated production of reactive quinones, which decrease the nutritive value. Herbivory upon new stems led to an increase in the number of resin glands that provide defense against mammalian herbivores. Herbivory also had a substantially negative effect on B concentration in leaves of B fertilized seedlings. We postulate that B nutrition of trees may play a significant role in the induced defense of birches.

Boron (B) is an essential micronutrient, whose deficiency is common in boreal forests. Our aim was to investigate the effects of the B supply on the retranslocation of micro-and macro nutrients in seedlings of Betula pendula Roth. One-year-old seedlings were grown under three different levels of B: 0%, 30% and 100% of the standard level for complete nutrient solution. Half of the seedlings were harvested after summer period and another half when leaves abscised. Boron was not resorbed in significant amounts from senescing birch leaves prior to abscission. The only micronutrients resorbed were Zn and Ni. Three macronutrients, N, P, and S, were resorbed efficiently from senescing leaves and accumulated into the stems. The resorption of nutrients was the mostly pronounced in B0 seedlings and minimal in B30 seedlings, which, however, showed the highest accumulation of nutrients during autumn period at least partly independently from the resorption from senescing leaves. Boron was shown to be an immobile element in silver birch seedlings that was not withdrawn from senescing leaves prior to abscission. This may increase the B availability for other tree species but also increase the potential for its leaching.