Materials and methods
In August 2017, we evaluated 94 sites of saline land in Yellow River
Delta (37º33′-38º09′N, 118º35′-119º13′E), China, with 0.50–19.24‰ soil
salinity (Fig. S1), and pH 7.04-8.08 (Fig. S2). Vegetation types
primarily included crops (maize, cotton etc.), Phragmites ,Tamarix chinensis , Suaeda salsa , and mudflat.
Five soil cores were randomly collected at each site, pooled, and
homogenized into a representative soil sample. Soil
pH(1:2.5 w/v) was determined using a pH meter; total
soluble salinity concentration measured by gravimetric method with water
ecxtraction (Chi et al., 2019). Carbonate was determined by Acid-base
titration, representing SIC (Fu et al., 2020); SOC was analyzed on a
Vario MACRO Cube (Elementar, Langenselbold, Germany) after removing SIC
with hydrochloric acid. Amino sugars and microbial residues were
analyzed using previously reported methods (Zhang and Amelung, 1996;
Engelking et al., 2007).
Generalized linear regression models were developed to assess
associations among SIC, SOC, and microbial residues (R software).
Structural equation modeling (SEM) was performed to trace causality
among SIC, microbial residues, and SOC via root-mean-square error of
approximation (AMOS software).