Microbial performance in soils along a salinity gradient under acidic conditions

The aim of our research was to study how a gradient in salinity under low pH conditions affected activity, community structure, and biomass of soil microorganisms. The study was conducted near Heringen, Germany, at five sites in the floodplain of the river Werra, which were affected by saline liquid residues from potassium mining injected into the underground,geological formations. The content of soluble salts ranged from 2.1 at site 1 to 9.7 mg g(-1) soil at site 5. Soil pH ranged from 3.85 to 4.55. Microbial biomass C, biomass N, fungal ergosterol and adenosine triphosphate (ATP) were highly significantly interrelated with correlation coefficients between r = 0.89 and 0.96 (P < 0.0001, n = 25). All soil biological properties except adenosine monophosphate had highest values at the low saline site 1 and lowest at the most acidic and most saline site 5. The strongest decrease with salinity was shown by ATP and ergosterol, achieving only 12 and 4% of the site 1 values, respectively. The ATP-to-microbial biomass C ratio declined to 46% of the maximum level at site 1, the microbial biomass C-to-soil organic C ratio to 38%, and the ergosterol-to-microbial biomass C ratio to 19%. All microbial indices, except basal respiration, exhibited strong salinity effects due to shifts in the microbial community structure towards prokaryotic microorganisms. Consequently, salinity is one of the most stressing environmental conditions for soil microorganisms. (C) 2003 Elsevier Science B.V. All rights reserved.