Parameter Tree:
EARTH SCIENCE > BIOSPHERE > VEGETATION > NITROGEN

Definition:
Nitrogen is a plant nutrient that is a component of proteins, nucleic
acids, coenzymes, and chlorophylls. Plants that are deficient in nitrogen
have stunted growth, and light-green older leaves.  


Reference:
Starr, C. and R.Taggart. 1998. Biology: the unity and diversity of life.
Wadsworth Publishing Company. Belmont, California.