What additional barriers do most plants possess to defend against pests?

Most plants possess a variety of defense mechanisms to protect themselves against pests, and one significant category of these mechanisms is chemical barriers. Chemical barriers include the production of secondary metabolites such as alkaloids, terpenoids, and phenolics, which can deter herbivores or even inhibit their growth. Some plants may produce toxins that are harmful if ingested, effectively acting as a poison to prevent pest infestation. This chemical defense is often coupled with other strategies, such as physical barriers (like thorns or tough leaves), but the focus here is specifically on the chemical aspects.

While physical barriers are important, they do not encompass the full range of defenses that plants use against pests. The defense strategy of developing long roots primarily aids in water and nutrient absorption rather than directly deterring pests. Color pigments may serve various functions, including attracting pollinators or regulating temperature, but they are not specifically aimed at defending against pests in the same way that chemical compounds are. Thus, chemical barriers represent a crucial and common method by which plants fend off pests effectively.