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).