In stem-changing -ir verbs in the present subjunctive, the stem change only occurs in the nosotros and vosotros forms, while in stem-changing -ar and -er verbs, the stem change occurs in all forms except nosotros and vosotros. Additionally, in stem-changing -ir verbs, the e or o in the stem changes to ie or ue, while in -ar and -er verbs, the e or o in the stem changes to ie or i.
