Vario el cube chnos elemental analyzer

Elemental Analysis: The C and N content in plant samples were measured using an elemental analyzer (vario EL cube CHNOS Elemental Analyzer, Elementar Analysensysteme GmbH, Germany). The P and K content were determined through HNO₃–H₂O₂ digestion and ICP-OES (iCAP 6300 ICP-OES Spectrometer, Thermo Fisher, USA). Meteorological data were derived from long-term observations at three different altitudes: 3500, 3900, and 4300 m. Given the absence of meteorological data at 2500 m, we selected meteorological data at altitudes of 3500, 3900, and 4300 m for principal component analysis (PCA) in correlation with the nutrient content of corresponding forest plants to ensure the uniformity of meteorological instrument performance. The meteorological instruments were installed within the forest, and the system was programmed to automatically calculate and store the observed meteorological data every 10 min. Data loggers were produced by Onset Company, USA (HOBO H21-USB).

Soil water content (SWC) was determined by using a drying method where each soil sample was measured for fresh weight, dried at 105°C for 48 h, then weighed. SWC was calculated using the equation: $$\mathrm{SWC}=\left(\text{Fresh weight}-\mathrm{Dry}\text{weight}\right)/\mathrm{Dry}\text{weight}\times 100\%.$$
Elemental analyzer (Vario EL Cube CHNOS Elemental Analyzer, Elementar Analysensysteme GmbH, Germany) was used to measure soil total carbon (TC) and total nitrogen (TN). Soil total phosphorus (TP), manganese (Mn), zinc (Zn), calcium (Ca), and potassium (K) contents were measured by X‐ray fluorescence spectrometer (Panalytical AXIOS mAX, Malvern Panalytical Ltd, The Netherlands).

All reagents (purchased from Aladdin Chemical Corporation, Shanghai, China) used for preparing antioxidants were of analytical grade and used without further purification. Commercial synthetic ester base oil of TIDTM was used as the base oil without further treatment. ¹H-NMR spectra were recorded in DMSO-d₆ solution on a Varian Mercury-Plus 400 spectrometers (Varian, Palo Alto, CA, USA) at 400 MHz and chemical shifts were recorded in parts per million (ppm) with TMS as the internal reference. FTIR spectra were recorded on a Thermo Nicolet NEXUS 670 FTIR Raman spectrometer (Thermo Nicolet Corporation, Madison, WI, USA). Mass spectra (MS) were obtained on a Finnigan LTQ XL mass spectrometer (Palo Alto, CA, USA) and signals were given in m/z. Elemental analysis were performed with a Vario EL cube CHNOS elemental analyzer (Elementar, Hanau, Germany).