Effects of precipitation on stoichiometry of biological soil crusts in a desert steppe of Northern China

Biological soil crusts are fundamental components and surface landscape in arid regions, and biogeochemical process also depends on them. However, biological soil crusts stoichiometry remains largely unknown in the desert region of Northern China. The influences of precipitation on biological soil crusts stoichiometry is also lacking in desert steppe. This paper aims to investigate the effects of precipitation on the stoichiometry of biological soil crusts in desert steppe. This field study was conducted at Dashuikeng Grassland Research Station, Yanchi County (106°58'E, 37°24'N, average elevation, 1 560 m), Ningxia Hui Autonomous Region, China. This region covers a large ecosystem of desert steppe that characterized by low rainfall and uneven precipitation, along the southwest edge of the Mu Us Sandy Land. In the study desert steppe area on the southeastern margin of the Tengger Desert, the average annual precipitation was only 298.3 mm during the 60 years from 1959 to 2019. The precipitation was regulated by the measurement of artificial rain using rainwater shed and sprinkler irrigation technologies, in order to evaluate precipitation effects on the biological soil crusts in desert steppe compared with natural precipitation. 28 precipitation treatments (6 m×6 m) were set up at the test station in early March 2018, where 3 m wide buffer zone was designed between each time. Control conditions of precipitation were designed via the shelter and sprinkler irrigation system, including 7 precipitation treatments, natural precipitation (CK), drought (1/2 reduction in precipitation, DW1/2 treatment, 1/3 reduction in natural precipitation, DW1/3 treatment, 1/4 reduction in precipitation, DW1/4 treatment), and increasing precipitation (1/2 increase in natural precipitation, IW1/2 treatment, 1/3 increase in natural precipitation, IW1/3 treatment, 1/4 increase in natural precipitation, IW1/4 treatment). Each treatment has 4 spares for the reproductivity. In the same period, small weather stations were set up in the test area. TRIME-PICO TDR Portable Soil Moisture Meter (made in Germany) was used for the data collection of precipitation in the soil water depth of 10 cm. Carbon (C), nitrogen (N) and phosphorus (P) contents of biological soil crusts were measured to examine the C: N: P stoichiometry and its driving factors. Three findings can be achieved: 1) Water-reducing treatment was beneficial to the enrichment of C, N and P in the crust. DW1/4 treatment and natural precipitation treatment posed significant effects on the C content in the crust layer and underlying soil. The water-reducing treatment can reduce the N level of the crust, while increase the N level of the underlying surface. The content of P in the crust layer was the lowest under DW 1/3 treatment, whereas the content of P in the underlying surface reached the peak under DW 1/2 treatment; 2) Natural rainfall and increased precipitation can significantly improve the underlying surface C: N and C: P. There was a reduction of N: P in the crust layer and its underlying surface; 3) Suitable soil moisture conditions promoted the accumulation of SMBC (Soil Microbial Biomass Carbon) and SMBN (Soil Microbial Biomass Nitrogen) on the crust layer and underlying surface, while excessive rainfall caused the loss of soil nutrients, which was not conducive to the accumulation of SMBC and SMBN. The relatively dry soil environment was conducive to the enrichment of soil carbon and nitrogen in the crust layer, provided more nutrients for soil microbial respiration, and was conducive to the accumulation of SMBC and SMBN. In short, the C: N: P stoichiometry of biological soil crusts and underlying surfaces had different responses to precipitation in the desertification areas of northern China. © 2020, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.