phytotoxicity

thumb|300x300px|Phytotoxic effects of the fungus Rhytisma acerinum on a Maple leaf. Phytotoxicity describes any adverse effects on plant growth, physiology, or metabolism caused by a chemical substance, such as high levels of fertilizers, herbicides, heavy metals, or nanoparticles. General phytotoxic effects include altered plant metabolism, growth inhibition, or plant death. Changes to plant metabolism and growth are the result of disrupted physiological functioning, including inhibition of photosynthesis, water and nutrient uptake, cell division, or seed germination.

== Fertilizers == High concentrations of mineral salts in solution within the plant growing medium can result in phytotoxicity, commonly caused by excessive application of fertilizers. For example, urea is used in agriculture as a nitrogenous fertilizer. However, if too much is applied, phytotoxic effects can result from urea toxicity directly or ammonia production from hydrolysis of urea. Organic fertilizers, such as compost, also have the potential to be phytotoxic if not sufficiently humified, as intermediate products of this process are harmful to plant growth.