Fatty acid extraction and quantification
As an independent measure of fungal biomass, we quantified phospholipid fatty acids (PLFA) from approximately 10 g of freeze-dried soil from each mesocosm pot. Briefly, lipids were extracted by a commercial laboratory (Microbial ID, Newark, DE, USA), using methods described in Frostegård et al . (2011) and Waller et al. (2020). We used the PLFA fungal biomarker 18:2ω6 to assess biomass of non-arbuscular mycorrhizal fungi.