Why isn't the first letter of a subtitle in uppercase in bibliographies?
Some styles that require sentence case, such as APA, also require that the first letter of the subtitle following a colon also be uppercase (“Age and environmental sustainability: A meta-analysis”). Zotero and CSL cannot currently produce this format natively. You can install the Propachi plugin in Zotero and enable its Uppercase Subtitles option to produce this format automatically. When using the Propachi plugin in this way, store the main title (before the colon) in the “Short Title” field.