Abstract:

Biological soil crusts are fundamental components and surface landscape in arid regions， and the main source of soil nutrients also depends on them. However， the rainfall pattern affects the stability of the regional ecosystem in the desert region of Northern China. This paper aims to investigate the effects of precipitation on soil organic carbon， total nitrogen and microbial characteristics of biological soil crusts in a desert steppe. 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. 12 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 rainwater shed and sprinkler irrigation system， comprising 3 precipitation treatments， natural precipitation （CK）， -50% （50% reduction in precipitation）， and +50% （50% increase in precipitation）. Each treatment had 4 replicates for statistical evaluation of the reproducible. In the same period， small weather stations were set up in the test area. We collected soil samples from each site stratified into three soil depths： the crust layer （0-0.5 cm）， a middle layer （0.5-3.0 cm） and deep layers （3-10 cm）. There were three main findings： 1） The -50% was conducive to the accumulation of soil organic carbon （C） and soil microbial carbon （SMB-C） and increased the presence of soil fungi， while also increasing the soil total nitrogen （TN） content and presence of fungi in the crust layer and middle layer. +50% increased the number of soil bacteria in each soil layer， the crust layer and the soil microbial biomass nitrogen （SMB-N） content in the middle layer， and significantly reduced the soil C∶N， SMB-C∶SMB-N in each soil layer and number of fungi： ratio of number of bacteria， the contents of SOC， SMB-C， SMB-N， and the number of bacteria and fungi under different precipitation treatments all decreased significantly with soil depth； 2） Bacteria were more sensitive to precipitation reduction， while fungi were more resistant to aridity than bacteria. Soil bacteria and fungi had different adaptation strategies to changes in precipitation. 3） The -50% treatment was beneficial to the restoration of soil nutrients， especially to the restoration of soil nutrients in the middle layer underlying the crust layer， while the +50% treatment resulted in slight degradation of the crust layer and decreased deep layer soil nutrients.

Key words: carbon, nitrogen, microbial characteristics, biological soil crusts, precipitation, desert steppe