Na 1500 series 2

Soil total carbon (Ctot) and total nitrogen (Ntot) were determined by the Dumas method (NF ISO 13878). Briefly, the Dumas method consists of flash combustion of the soil sample (at 1000 °C) using helium and oxygen. After purification of the combustion gases, determination of total carbon and nitrogen contents was performed by chromatography with a thermal conductivity detector (NA 1500 series 2 CARLO-ERBA).
Total phosphorus (Ptot) was determined after the acid digestion of soil samples, as previously described. The HPO₄ formed during acid digestion was measured after adding ammonium molybdate and ascorbic acid [31 (link)] using the recommendations of the Spectroquant^® phosphate test (ref: 114848). The color produced by phosphomolybdenum (PMB) was measured by colorimetry at 885 nm (Genesys 10 µv Scanning, Thermo).

Soil total carbon (Ctot) and total nitrogen (Ntot) were determined by the Dumas method (NF ISO 13878) by gas chromatography with a thermal conductivity detector (NA 1500 series 2 CARLO-ERBA, Val-de-Reuil, France).
Total phosphorus (Ptot) was determined after the acid digestion of soil samples, as previously described by the ammonium molybdate and acid ascorbic method [30 (link)]. The color produced by phosphomolybdenum (PMB) was measured by colorimetry at 885 nm (spectrophotometer Genesys 10 µv Scanning, Thermo Scientific, Armand Asnières-sur-Seine, France).
Water extractions were performed to measure total dissolved organic carbon concentrations (DOC), with a Shimadzu TOC-500 apparatus (Shimadzu, Kyoto, Japan). One gram of soil was shaken for 24 h in a polypropylene centrifuge tube with 10 mL of ultrapure water. The suspensions were centrifuged at 2000 rpm for 10 min, and supernatants were filtered at 0.2 µm (PTFE, VWR©) and directly analyzed on the TOC analyzer.