Soil physiochemical measurements
Soil pH, gravimetric water content, and clay concentration were measured
using modified Long-Term Ecological Research (LTER) protocols (Robertsonet al. 1999). Briefly, soil pH was determined in a 1:1 (weight to
volume) solution using 15 g of field-moist soil and 15 ml of Milli-Q
water (Millipore Sigma, Burlington, MA, USA). The solution was measured
on a Hannah Instruments (HI; Woonsocket, RI, USA) 3220 pH meter equipped
with a HI 1053B combination glass pH electrode, designed for use with
solid suspensions. For determining gravimetric water content,
approximately 7 g field-moist soil was dried at 105 ÂșC for a minimum of
24 h. Soil texture was measured on oven-dried and sieved soil using the
hydrometer method following Gee & Bauder (2018).
Prior to soil total organic C and N analysis, soils were freeze-dried
using a Savant Novalyphe-NL500 freezer dryer (Savant, Farmingdale, NY,
USA) and ground to a fine powder using a roller mill. If effervescence
occurred when a drop of 1 M HCl was added to a subsample of each soil
sample, then inorganic C was removed from 2 g of the soil sample by
twice-washing with 30 mL 0.1 N HCl (allowing the soil slurry to stand
for 1 h during each wash), twice-washing with 30 mL DI, and then
freeze-dried. The soil samples were analyzed for total organic C and
total N by continuous-flow, direct combustion using a Vario Micro Cube
elemental analyzer (Elementar, Hanau, Germany).
Microbially available orthophosphate, referred hereafter as Olsen P, was
estimated by extracting 1 g of soil with 200 ml of 0.5 M
NaHCO3 at pH 8.5 (Olsen et al. 1954). Briefly,
slurries were shaken for 30 min and filtered through Whatman No. 42
filters. Orthophosphate was measured colormetrically using a Lachat AE
Flow Injection Auto Analyzer (Method 12-115-01-1-Q, Lachat Instruments,
Inc., Milwaukee, WI, USA).