Root biomass, root colonization, and microbial biomass
All roots that were inside of the cores were separated from soils and washed in the lab. Dry root biomass was measured, and microbial biomass C was measured from a subsample of soil from each core using chloroform slurry fumigations (Witt et al., 2000) followed by persulfate digestion to CO2 (Doyle et al., 2004; Kane et al., 2022). In brief, soils were extracted in potassium sulfate with and without chloroform for 4 hrs. Filtered supernatant was digested in persulfate solution where dissolved C was oxidized to CO2. Total CO2 and δ 13CO2 was measured on a Picarro G2201 (Picarro Inc). Microbial biomass C was calculated as the difference between chloroform-fumigated and non-fumigated samples scaled by 2.64 (Vance et al., 1987) and litter-derived microbial biomass was determined using two endmember isotope mixing models.
A sample of roots were separated for root arbuscular mycorrhizal (AM) colonization measurements. To remove pigment, root samples were cleared in 10% potassium hydroxide followed with 85% ethanol to leach excess pigmentation. Roots were acidified in 5% hydrochloric acid and then stained for 5 minutes in 0.05% trypan blue (Comas et al., 2014). AM colonization was determined by suspending root samples in water on a 1x1cm gridded petri dish and measuring how often arbuscules or hyphae were present at each root-gridline intersect (Giovannetti & Mosse, 1980).