2.2.2. Plants nutrient analysis
Plant simples were ground using a ball mill (Retsol MM2000, Retsch, Haan, Germany). Subsamples of shoots and roots were digested with a mixture of nitric and perchloric acid (4:1) (Jin et al., 2012). The concentrations of K in the digest solution was determined with a flame photometer (Liu et al., 2020). The P concentration were measured by SKALAR San++ continuous flowing analyzer after acidic digestion (Xu et al., 2018). The concentrations of N in plant tissues were determined using an Elementar CNS analyser (Vario EL III, Elementar Analysensysteme GmbH, Germany) (Li et al., 2019b).
2.2.3. Available nutrientsin the rhizosphere
The rhizosphere soils were collected by shaking the roots and the soil adhering to the roots was considered as rhizosphere soil (Nazih et al., 2001). All soil samples were stored in a refrigerator at 4 °C for further analysis.
Soil available N (NH4+ and NO3-) was determined with the methods described by Miah et al. (1998). Soil Olsen P was obtained by extraction in NaHCO3 and analyzed by the Mo-Sb colorimetric method (UV2550, Shimadzu, Japan) (Bao, 2000). Available K was extracted with neutral 1 M NH4OAc, and K concentration was measured by a flame photometer (Chen and Gabelman, 1995).