%G+C profiling and cross hybridisation of microbial DNA reveals great variation in below-ground community structure in UK upland grasslands

Total DNA was directly extracted from microbial populations in grassland soils taken from three geographically distinct upland sites at Garrigill, Aber and Sourhope, UK. Within each site, grasslands were categorised using the National Vegetation Classification into distinct vegetation sequences, namely unimproved, semi-improved and improved. Microbial community DNA was extracted from the different soils and analysed by determining (percent guanine+yctosine) %G+C profiles by thermal denaturation, and by cross hybridisation to measure the degree of similarity between the DNA extracted from the different soils. The %G+C profiles indicated that the microbial community structure within the different grasslands at Garrigill was significantly different. No significant differences in %G+C were detected under the different grasslands at Aber and Sourhope. However, significant differences in %G+C profiles derived from spatially-distinct replicate quadrats taken within grasslands were detected within the semi-improved grasslands at each site, and the unimproved grassland at Aber. Cross hybridisation analysis revealed significant differences between the improved, semi-improved and unimproved grasslands within all sites, with similarity values ranging from 51 to 94%. Significant differences were also detected between replicate quadrats within grassland types by this technique. These results provide evidence for great spatial variation in community DNA (i.e. genetic composition of microbial communities) within these grasslands. (C) 2000 Elsevier Science B.V. All rights reserved.