**2. Materials and Methods**

### *2.1. Plant and Soil Preparation*

We established experimental grassland microcosms with typical sodic saline meadow soil from the Songnen Meadow Ecological Research Station (44◦45 N, 123◦45 E), Northeast Normal University, Jilin Province, in northeastern China; this area has a semiarid temperate-zone monsoon climate and typical characteristics of a continental climate. The soil pH was 8.2. The vegetation of the experimental site is dominated primarily by *S. viridis*, *L. chinensis*, and *S. corniculata*. *S. viridis* is an indigenous C4 grass that associates strongly with AMF. *L. chinensis* is a C3 grass that gains little benefit from association with AMF [40,41], and *S. corniculata* is a member of the Chenopodiaceae family. The seeds

of the three species and soil were collected from the Songnen meadow and were stored in a refrigerator at 4 ◦C before being used.

Topsoil (0–30 cm) was collected from the same site from which the plant seeds were collected. The soil was sieved (2 mm sieve) to remove large stones and plant roots and was sterilized twice using high-pressure steam at 121 ◦C for two hours each time to eliminate indigenous AMF.

We collected soil (500 g) from the Songnen meadow where warming and N input had been applied for five years and where Medicago sativa had been cultivated in 200 g of sterilized soil for four months. After the four month period, the aboveground biomass was removed, and the inoculum comprised spores, infected root fragments, hyphae, and soil (approximately 2000 spores per 50 g of soil).
