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Subdomains are considered separate sites and so normally you would consider all the link metrics separate.  That is why the most common advice is to use subdirectories for content sections vs subdomains.  That way any link equity/page rank you acquire for links into the subdirectory flow up to the main domain. You also need to be careful not to run into duplicate issues with a www vs non www versions of your site as those two subdomains are seen as separate entities by google. If you want to consolidate link equity, 301 redirect all the pages in the blog subdomain (i.e. blog.root.com) to the equivalent subdirectory (root.com/blog) then you can have a unified single set of pages/URLs to focus on.