What can trigger a tree's energy allocation toward growth when nitrogen fertilization is applied?

When nitrogen fertilization is applied, it influences the energy allocation within a tree. In this context, defense mechanisms are particularly relevant because trees often allocate resources to growth and development in response to nutrient availability. Nitrogen is an essential nutrient that not only aids in the synthesis of amino acids and proteins but also plays a critical role in various physiological processes.

When nitrogen levels increase due to fertilization, the tree can enhance its growth, which includes producing new leaves, stems, and roots. However, part of this growth can also involve increased allocation to defense mechanisms such as the production of secondary metabolites and thicker bark, which help the tree defend itself against pests and diseases.

This opportunity for increased growth can sometimes conflict with the tree's need to defend itself from external threats. In essence, when nitrogen is available, trees focus on growth, but they also need to ensure that they can defend against herbivory and pathogens, thereby triggering energy allocation toward defense as well.

Root development, flower production, and wood density are also influenced by nutrient availability, but the immediate and general response of trees to increased nitrogen is more closely associated with their defensive responses, making the choice regarding defense the most fitting in this context.