2.2 Experimental design and analysis method
Qaidam Basin was dominated by alpine deserts, we selected typical
deserts soil samples soil nearly 10 km upper 30 cm mixture. Thus, all
223 observations were collected in this study (Fig. 1). Samples were
deposited for air drying, and then passed through a 0.25 mm soil mesh
sieve.
Soil organic carbon contents were analyzed by TOC-5000A analyzer
(Shimadzu corporation, Japan) using dry oxidation method. TN and TP were
analyzed by Elemental Analyzer (PE2400ⅡCHN, German) and perchloric acid
sulfuric acid dissolution molybdenum antimony anti colorimetry.
Furthermore, pH was measured by automatic titrator with a pH
(H2O) probe (PHS-3C, China). Altitudes were tested by
global positioning system (GPSMAP 66s, China). Average monthly climate
data (January 2020) is downloaded from http://worldclim.org for
1970−2000 with 1 km2 spatial resolutions (Fick and
Hijmans 2017).
Statistics
Cluster analysis of SOC and TN
were conducted by multivariate
regression trees through “mvpart” package in R-3.3.4 version. Drive
factors of climate factors and soil characteristics on SOC and TN were
analyzed by structural equation
model using “piecewiseSEM” package. SOC contents were predicted based
on climate factors by generalized additive models (mgcv).