Microbial community structure and nutrient availability in oil sands reclaimed boreal soils

Alberta has one of the largest oil reserves in the world, some of which is extracted by surface mining representing a large scale disturbance to forest soils. We examined ecosystem function in reclaimed soils by measuring microbial community structure with phospholipid fatty acid (PLFA) analysis and nutrient availability with plant root simulator (PRS (TM)) probes. Samples were taken from three slope positions, at three sites, on three dates (June and August 2005, and August 2006), and non-metric multi-dimensional scaling ordination was used to examine trends in the data. Repeated measures ANOVA was used to examine trends over time in key response variables identified by ordination. Ordination results revealed distinct differences between the spring and summer microbial community structure across sites, although large site differences were also found between fall measurements in the two consecutive years. Total microbial biomass (TMB) and the fungal to bacterial ratio (FBR) emerged as key response variables for microbial community structure, and repeated measures ANOVA indicated significant site differences for these parameters. Soil nutrient availability was predominantly affected by site, but was also greatly affected by season and by year of sampling. The key response variables for nutrient availability were NH4+ and NO3-, which also varied significantly by site and season, with high NH4+ availability in the spring on vegetated/fertilized sites and high NO3- availability year round on the non-vegetated site. Slope position had an inconsistent effect on the measured parameters which may indicate that these reclaimed soils are not characterized by near surface lateral flow. Seasonal fluctuations in nitrogen and boron availability, reflected in microbial community PLFA profiles, point at possible mechanistic linkages between the functioning of microbial communities and soil mineral nutrient availability. (C) 2009 Elsevier B.V. All rights reserved.