Challenging the “resource allocation” paradigm: a meta-analysis on how nitrogen fertilization balances plant growth and defense against insects

The activation of plant defenses against pest and pathogen attack is often associated with suppression of growth. This physiological antagonism is commonly explained by limitation of resources, such as mineral nutrients, which may be allocated to defense at the expense of growth, or vice versa. Despite recent evidence questioning the simplicity of this “resource allocation” paradigm, it remains a prevalent concept in plant immune studies. Nitrogen (N) is one of the most important mineral nutrients for plant development, and studies have highlighted its involvement in plant responses to biotic factors . This wealth of evidence provides a unique tool to test the resource allocation theory: if growth and defense are limited by resource availability, are both processes promoted with an increase in N supply? Here we conducted a meta-analysis to evaluate the effects of N on plant growth and defense. Our results revealed that N fertilization increases overall plant traits associated with growth, such as plant height and biomass accumulation. However, there is little evidence for an upregulation in plant defense traits under improved N supply. In fact, our meta-analysis indicates that an increase in N availability also promoted the development of herbivorous insects, increasing larval mass and survival on plants. This data suggests that an increase in resource availability favored plant growth over defense. These findings add to growing evidence that challenges the simplicity of the resource allocation paradigm, underscoring the critical role of N in balancing plant growth and defense, particularly in agricultural systems.