Open access publications in the SLU publication database

Abstract

Monitoring and assessment of agricultural soils has become requested as means to detect changes in soil quality. Among possible microbial indicators for monitoring soil quality, the most common methods include microbial biomass, respiration, N mineralization and a community profiling method. Among the latter, the most used seem to be DGGE (denaturing gradient gel electrophoresis), PLFA (phospholipid fatty acids), and CLPP (community level physiology profile) analyses. Here we report results from an investigation of the PLFA analysis for the possible use as an indicator for monitoring soil quality. Soil samples were taken 2009 in the Ultuna soil organic matter field experi-ment, which was started in 1956 for investigating the long-term effect of mineral N fertilizers and different organic amendments on crop yields, soil organic matter changes and soil physical properties. PLFAs were extracted from top- and subsoils in ten treatments. PLFA concentrations were compared to other variables, such as total carbon, total nitrogen, pH and respiration, but also to other results reported earlier from the same experiment. Total PLFAs in topsoil samples (0-20 cm) were highest in the sewage sludge (O) treatment, which was almost reflected in subsoil samples, although the highest mean value among those samples was found for the farmyard manure (J) treatment. A good correlation was observed between total PLFAs in topsoil samples and total carbon, but total PLFAs were even better correlated with total nitrogen (r=0.81; p<0.0001). Subsoil samples (27-40 cm depth) reflected topsoil samples for total PLFAs, but the individual PLFAs revealed that the composition of the microbial communities were entirely different. The presence of cyclic fatty acids in the sewage sludge treatment indicated some kind of stress for gram-negative bacteria, probably caused by heavy metals, although a negative effect of the sewage sludge application could not be seen in other ways, e.g. crop yield. In conclusion, the PLFA analysis can give valuable information about the microbial community in soil samples. It can be used in a monitoring programme, although the recommendation is that it would be preferable to combine the PLFA analysis with other methods, for example CLPP, in order to determine trends and changes of microbial communities and activities in soils.