Which suffix is related to the treatment or specialty of a field?

The suffix that signifies treatment or a specialty in a specific field is -iatry. This suffix is derived from the Greek word "iatreia," which means healing or medical treatment. It is commonly used in medical terminology to denote various medical specialties focused on the treatment of diseases and disorders. For instance, "psychiatry" pertains to the treatment of mental illnesses, and "podiatry" refers to the treatment of conditions affecting the feet.

The other suffixes mentioned do not signify treatment in the same manner. The suffix -logist refers to a specialist in a particular field (as in "biologist"), while -plasty indicates a surgical repair or reconstruction (as in "rhinoplasty" for reshaping the nose). Meanwhile, -itis typically denotes inflammation (as in "arthritis"), rather than focusing on treatment or specialization. Therefore, -iatry is the appropriate choice when discussing a suffix related to the treatment or specialty of a field.