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).