(ほぞん) Preserve – usually used with traditional culture or morals more than environmental causes. You’ll often see this:保存員会(ほぞんいんかい, meaning, preservation committee)
する(ほご する) Conserve, protect:can be used about protecting nature and the environment. But usually used with police protection (for snitches) or if you’re escorting a lost child or drunk to the police box.
(ほしゅ) Doesn’t mean conserve at all! It means maintenance or upkeep of equipment or facilities.
(CAREFUL: A conservative person is 保守的な(ほしゅてきな)人)