Influence of synthetic sheep urine on the microbial biomass, activity and community structure in two pastures in the Scottish uplands

The impact of urine on the microbial biomass, activity and community struct ure was compared in the soil beneath two pastures in the Scottish uplands; Fasset, a natural Agrostis capillaris-Festuca ovina-Galium saxatile grassla nd and Strathfinella, a semi-natural grassland, improved with fertiliser ad dition. Community level physiological profiles (CLPP) were used to characte rise the microbial communities. The utilisation of sugars, oligosaccharides , alcohols, carboxylic acids, long chain aliphatic acids, acidic, basic and neutral amino acids, amide N, phenolic acids and long chain aliphatic acid s was used to compare the soils and the impact of synthetic urine addition. In the untreated soils, the utilisation of all the substrates decreased fr om the first week in May through to October. Averaged over all times and ur ine treatment, the potential utilisation of all substrates except for pheno lic acids, long chain aliphatic acids and carboxylic acids was greater in t he improved and more intensively grazed Strathfinella site. When averaged o ver all sample times, urine increased the utilisation of sugars, oligosacch arides, basic amino acids and amide N and the increases were greater in the unimproved, less intensively grazed, Fasset soil than that at Strathfinell a. The effect of urine tended to be greatest during the period between 2 an d 5 weeks after urine addition when utilisation of alcohols, acidic and neu tral amino acids was also increased. Microbial biomass C in the control soi ls was 155.9 and 112.7 g C m(-2) at Fasset and Strathfinella, respectively. Values did not change significantly with time and were unchanged by the ad dition of urine. However, urine addition significantly increased basal resp iration rates at Fasset and decreased them at Strathfinella. Urine also inc reased bacterial numbers in both soils, but had no consistent effect on fun gi or yeasts. The significance of these findings for studies of soil microb ial community structure and activity in grazed upland grasslands is discuss ed.