Soil properties and microbial activity across a 500 m elevation gradient in a semi-arid environment

Abstract

If climate change causes the semi-arid shrub-steppe to become hotter and drier it may affect soil C and N cycling and precipitate changes in soil processes and microbial and plant community structure. This study was conducted, using an elevation gradient as an analog of climate change, to analyze climatic influence on soil microbial activity and soil properties. We collected soil from under cryptogamic crust and bunchgrass plants at 25 sites over a 500 m elevation transect in a shrub-steppe ecosystem located in eastern Washington State of the US. The samples were analyzed for several chemical and microbiological attributes including pH, microbial biomass and nitrification potential and the data grouped into five climate sites for statistical analysis. Soil pH decreased over the transect with higher pH values in the grass soil than the crust. In contrast soil electrical conductivity (EC) increased with increasing elevation as did both ammonium and nitrate. Ammonium and EC were greater in the crust soil than the grass soil but nitrate concentration was the same under both plant covers. Both total C and N amounts increased with elevation as did nitrification potential. Due to high sample spatial variability microbial biomass, respiration and N mineralization showed non-significant trends over the 500 m elevation transect. Using these measured gradient relationships the increase in temperature and decrease in precipitation that is expected in this shrub-steppe ecosystem over the next 100 years would eventually cause the pH to increase and the EC to decrease. Plants would become more sparse, nitrification potential would decrease and ammonium would increase. Total C, N and microbial biomass concentrations would begin decreasing and may shift the controlling factors of the ecosystem to abiotic factors. The changes in the cycling of N and to some extent C due to climate change could alter the microbial and plant community structure and function of this ecosystem and cause it to move in the direction of desertification.