5 900 svdv

Soil moisture content (M) was measured by the weight method. pH was measured with a water quality analyzer (Shanghai Lechen LC-MP-41 T). Soil electrical conductivity (EC) was measured at 10 cm soil level with a conductivity meter (SANXIN SX836). Other nutrients were assayed according to our previous study (Gu et al., 2023 (link)). Alkaline nitrogen (AN) and total nitrogen (TN) contents of soil were analyzed using the Analytik Jena Nitrogen Elemental Analyzer Multi-N/C 2100/2100S, Germany. Available phosphorus (AP) was extracted by NaHCO₃ and measured on a continuous flow analyzer (AMS Alliance, Futura, France). Soil total phosphorus (TP) was measured by wet digestion with HClO₄-H₂SO₄ and quantified using inductively coupled plasma emission spectrometry (Agilent 5,800 ICP-OES, United States). Available potassium (AK) was with CH₃COONH₄ (pH 7.0) and measured by inductively coupled plasma emission spectrometer (Agilent 5,900 SVDV, USA). Organic matter in soil was quantified using a potassium dichromate oxidation and carbon analyzer (OI Analytical Aurora 1,030 TOC, USA).

The whole root and shoot samples were ground into a fine powder using a Freezer Mill (SPEX SamplePrep) following the manufacturer’s instructions. Samples were then lyophilized in a Modulyo freeze dryer (Edwards, West Sussex, UK) for at least 48 h or until thoroughly dried, and then submitted for chemical analysis. The total N content of dried root or shoot samples was measured by the LECO CN628 combustion analyser following the manufacturer’s protocol. For elemental analysis, root and shoot samples were first digested using 85:15 (v/v) nitric acid:perchloric acid in an open tube digestion block. After volatilization of the acids, the residues were dissolved in 5% (v/v) nitric acid. Sample analysis was carried out with an Agilent 5900 SVDV inductively coupled plasma-optical emission spectrometer (ICP-OES).