2.1 Experimental site
The field experiment of this study has been carried out for 10 years since Da‘an Sodic Land Experiment Station (DASLES), Chinese Academy of Sciences (CAS) (45°35′58″~45°36′28″N,123°50′27″~123°51′31″E), which is located in Da‘an city of Jilin Province of China. The DASLES is a typical saline degraded grassland ecosystem located in the Western of Songnen Plain, . The area is semi-arid with a temperate continental climate. The annual mean temperature is 4~, the annual mean precipitation is 350~ in the area. While evaporation is about , which is 4~5 times of the precipitation.
The original field experiment was conducted in two different kinds of saline-sodic grassland: moderately saline-sodic grassland (MSSL), with soil pH 8.94 and ECe 5.7 dS m–1, and severely saline-sodic grassland (SSSL), with soil pH 9.80 and ECe 8.8 dS m–1. This study was only carried out in MSSL, for other basic chemical characteristics of grassland soils, please refer to our previous studies (Huang et al. , 2015 & 2019).