Effects of flue gas desulfurization gypsum by-products on microbial biomass and community structure in alkaline-saline soils

For an alkaline-saline region in Northwest China, we examined the responses of soil microbial communities to flue gas desulfurization gypsum by-products (FGDB), a new ameliorant for alkaline-saline soils. In 2009 and 2010, we collected soils from 0-20 cm and 20-40 cm depths along an experimental FGDB gradient (0, 0.74, 1.49, 2.25, and 3.00 kg FGDB m(-2)). As a measure of microbial community composition and biomass, we analyzed phospholipid fatty acids (PLFAs). We used real-time quantitative polymerase chain reaction (qPCR) to measure abundance of bacterial 16 S rRNA copy numbers. Additionally, physicochemical soil parameters were measured by common laboratory methods. Microbial community composition differed along the FGDB gradient; however, the microbial parameters did not follow a linear response. We found that, in 2009, total PLFA concentrations, and concentrations of total bacterial and Gram-negative bacterial PLFAs were slightly higher at intermediate FGDB concentrations. In 2010, total PLFA concentrations, and concentrations of total bacterial, Gram-positive bacterial, Gram-negative bacterial, and fungal PLFAs as well as the fungal:bacterial PLFA ratio were highest at 1.49 kg FGDB m(-2) and 3.00 kg FGDB m(-2). PLFA concentrations often differed between 2009 and 2010; however, the patterns varied across the gradient and across microbial groups. For both years, PLFA concentrations were generally higher at 0-20 cm depth than at 20-40 cm depth. Similar results were obtained for the 16 S rRNA copy numbers of bacteria at 0-20 cm depth. FGDB addition resulted in an increase in soil Ca2+ and NO (3) (-) -N and a decrease in pH and electrical conductivity (EC). Shifts in PLFA-based microbial community composition and biomass could partly be explained by pH, soil organic carbon, total nitrogen (TN), soil moisture, EC, inorganic nitrogen, C/N, and Ca2+. Indirect effects via shifts in abiotic soil properties, therefore, seem to be an important pathway through which FGDB affect soil microbial communities. Our results demonstrate that addition of FGDB leads to significant changes in soil physicochemical and microbial parameters. As such, addition of FGDB can have large impacts on the functioning of soil ecosystems, such as carbon and nitrogen cycling processes.