Natural antioxidants, such as ascorbic acid and carotenoid, have a function which is so important for fungal cells, particularly fungi that produce natural antioxidants (eg. carotenoids), because of its role as an antioxidant that acts to protect fungal cells against oxidation, especially photooxidation and photolysis, as well as against extreme environmental conditions. As an antioxidant, ascorbic acid or carotenoid is able to protect fungal cells from free radicals which is formed during photosynthesis. So it is assumed that this natural antioxidant is as quencer/damper of singlet oxygen, which is very effective and also is as a direct free radicals predator. Caroteoids, especially, has resilience in the process of absorbing singlet oxygen as a whole. Therefore, a molecule of carotenoid or other natural antioxidant may capture up to 1,000 molecules of singlet oxygen.
In addition to the above answer melanin acts as an antioxidant agent it used as scavenger for antioxidants just look for melanin and fungi in PubMed and you will get many papers describing the phenomenon and the mechanism.