Toc 5 csn total organic carbon analyzer

Soil pH was determined according to the method of King et al.^{26 (link)}. Specifically, 2 g of soil and 2 mL of DI water were placed into 15 mL centrifuge tubes and shaken horizontally for 1 hr at 175 rpm. Soil pH was then measured with an Oakton benchtop pH meter (OAKTON Instruments, Vernon Hill, IL, USA). Total water content of soil samples was measured by placing 1 g of soil of each sample in 15 mL conical sterile tubes left open to dry at 60 °C in an oven for 24 hrs. Water content was determined as the percentage of the ratio between the water loss and dry weight of the sample.
Dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) were measured using a modification of the method described in Weintraub et al.^{27 (link)}. 2 g of soil of each sample was shaken with 25 mL of 0.5 M K₂SO₄ for 1 hour. Solutions were then filtered using a 0.2 µm Isopore^TM membrane filter (Millipore, Darmstadt, Germany). DOC and TDN were measured using a Shimadzu TOC-V CSN Total Organic Carbon Analyzer with TNM-1 module.

For all soils from the end of the microcosm experiment, soil moisture, pH, TDN, extractable organic carbon (NPOC), and ammonium (NH4⁺) were evaluated. A subsample of each soil was dried at 100°C for 48 h to determine gravimetric soil moisture and adjust for real soil weight in all calculations. Immediately following collection of the final microcosm soil sample, 10 g of soil were extracted for 24 h in 40 mL of 2M KCl including 1 h of shaking. Extracts were filtered with Whatman no. 1 paper (Whatman Incorporated, Florham Park, NJ, United States) and frozen until analysis. NH4⁺ was measured on a BioTek Synergy 2 Multidetection Microplate Reader (BioTek, Winooski, VT, USA) and TDN/NPOC were measured on a Shimadzu TOC-V CSN Total Organic Carbon Analyzer (Shimadzu TOCvcpn, Kyoto, Japan). pH was measured with a ratio of 1.5 g dry soil: 3 mL water. Soils were shaken at 250 rpm for 1 h, allowed to equilibrate, and then tested on an Accumet Research AR10 pH meter.