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).