Spatial distribution of the abundance and activity of the sulfate ester-hydrolyzing microbial community in a rape field

PURPOSE: Sulfur (S) plays a vital role in plant metabolism, and the detrimental impact of S deficiency in several field crops has increased over the last 30 years. The bio-availability of organic S to plant depends on arylsulfatase (ARS), a key enzyme for S mineralization in soil. In this study, we characterized the spatial variability of ARS activity in an agricultural soil cropped with the rape plant (Brassica napus). Because rape requires relatively large amounts of S per yield unit compared to most grain crops, it is very sensitive to S deprivation similarly to the other plants of the Brassicaceae family, with consequences for seed quality and yield. MATERIALS AND METHODS: The spatial variability of (a) ARS activity, (b) the abundance of culturable bacteria possessing the ARS, and (c) soil properties (temperature, soil pH, SO 4 2− -S (sulfate-S) content, labile carbon (C) and nitrogen (N), soil microbial biomass carbon SMB-C, and nitrogen SMB-N) was estimated at 40 sites within a rape field, using a 4 × 5-m sampling grid. Geostatistics were used to model the spatial distribution of the measured variables, and relationships between variables were tested using linear statistical analyses. RESULTS AND DISCUSSION: The total ARS activity showed a low variability ranging between 69.0 and 153.1 μg p-nitrophenol g−1 dry soil h−1 while the abundance of the culturable ARS community ranged within one order of magnitude. The distribution of both the abundance and activity of the ARS community exhibited spatial dependence in 800 m2 agricultural field. CONCLUSIONS: The spatial pattern of ARS activity in the field was correlated with several soil properties, and results suggest that soil pH, labile C and N, and SBM-C/SBM-N ratio were the main parameters linked to the ARS activity rather than the abundance of the culturable ARS bacterial community or the SO 4 2− -S concentration.