## Materials and Methods
### Soil Analyses  
Soil chemical analyses on both the native and treated included EC, pH, INN, potentially mineralizable nitrogen (PMN), dissolved organic carbon (DOC), dissolved organic nitrogen (DON), total inorganic carbon (TOC), total nitrogen (TN), inorganic C (IC), plant-available phosphorus (AP), and total and available Pb and iron (Fe). Soil pH and EC were measured for greenhouse and lab-incubated soils at the beginning of the incubation, but only greenhouse soils at the end. Soil DOC and DON were tested at the beginning and end of the experiment. Inorganic C, TN, and TOC were only sampled once at the end of the experiment. Total and plant-available Pb and Fe concentrations were determined at the beginning of the incubation period, and available Pb and Fe were also measured at termination. All soil data were expressed on an oven-dried basis prior to statistical analysis. Soil pH and EC were determined using a glass electrode and an Oakton 2700 series benchtop meter at a 1:2 soil-to-water ratio. Inorganic nitrogen content was calculated by combining soil ammonium (NH4\({}^{+}\)) and nitrate (NO3\({}^{-}\)) into one parameter. Ten grams of fresh soil were added to 25 mL of two molar potassium chloride (2 M KCl), placed on a shaker for 30 min, and filtered through ash-free filter paper (Q5 Fischer Scientific, Waltham, MA, USA) [64]. The extract was then analyzed on a spectrophotometer microplate reader (UV-VIS Biotek Instruments, Highland Park, IL, USA) for NH4\({}^{+}\) using sodium salicate (Reagent A) and two percent bleach mixed with 1.5 M sodium hydroxide (Reagent B) [64]. Soil NO3\({}^{-}\) was also extracted using 2 M KCl and analyzed on the microplate reader following the vanadium chloride method [65]. Potentially mineralizable nitrogen (PMN) was assessed by incubating five grams of fresh soil in 12.5 mL of deionized water for 14 days at 25 \({}^{\circ}\)C to create an anaerobic environment [66]. Oxygen present in the headspace of the centrifuge tube was flushed with dinitrogen (N2) gas prior to sealing the tube. After two  
Figure 1: Graphical scheme of study design and analyses conducted. weeks, 12.5 mL of 0.5 M K\({}_{2}\)SO\({}_{4}\) was added, the mixture was shaken for 30 min, and filtered through ash-free filter paper (Q5 Fischer Scientific, Waltham, MA, USA). The resulting extract was then analyzed using a spectrophotometer microplate reader (UV-VIS Biotek Instruments, Highland Park, IL, USA), with PMN calculated as the difference between pre- and post-incubation NH\({}_{4}\)\({}^{+}\) concentrations. A subsample of dried biomass was finely ground with a Willey Mill (Willey Laboratory Mill, Model 4, Arthur H. Thomas Co., Philadelphia, PA, USA) and passed through a 1 mm screen. Ground plant material was wrapped in tin capsules and analyzed for total carbon (TC) and total nitrogen (TN) by dry combustion using a Carlo Erba CN 2100 CN analyzer (Carlo Erba Instruments, Milan, Italy). Soil TN comprised organic N, ammonia (NH\({}_{3}\)\({}^{-}\)), NH\({}_{4}\)\({}^{+}\), NO\({}_{3}\)\({}^{-}\), and nitrite (NO\({}_{2}\)\({}^{-}\)). Dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) concentrations were analyzed using the Newcomb-Carrillo method (2011) [67], with 1:2.5 soil:0.5 M K\({}_{2}\)SO\({}_{4}\) shaken for 30 min, stored at 4 \({}^{\circ}\)C overnight, and filtered through ashless filter paper (Q5 Fisher Scientific, Waltham, MA, USA). Samples were analyzed on a total organic carbon (TOC) analyzer (Shimadzu TOC-VCPH with TNM-1, Kyoto, Japan). Soil IC was determined via the pressure-calcimeter method outlined by [PERSON] et al. (2002) [68]. Total organic carbon was calculated as the difference between total C and IC. Available P was estimated using the Olsen P method [69]. Available concentrations of Pb and Fe were quantified through DTPA extraction [70] and analyzed using inductively coupled plasma-optical emission spectrometry (ICP-OES).