Reproducibility in the response of soil bacterial community-level physiological profiles from a land use intensification gradient

Abstract

This work assessed soil bacterial diversity through community-level physiological profiles (CLPP) over three consecutive years, at sites representing a gradient of land use intensification. The relationship between CLPP and soil physical and chemical properties, and the potential use of CLPP for soil quality monitoring was also evaluated. Samples were collected from sites under native vegetation (V0); naturalized prairie, cleared in 1982 (P16); conventional tillage, cleared in 1972 (T26); and direct drilling, cleared in 1958 (D40). Plate counts were performed to determine soil culturable bacterial density. Sample dilutions were inoculated on Biolog GN microplates, and optical density (OD) was recorded after 54 h of incubation. Richness (Ri), Shannon–Weaver index (H) and principal component analysis (PCA) on OD standardized data were performed. Soil aggregation evaluated through the variation between dry and wet average aggregate diameter (AAD), soil organic carbon (SOC) and total nitrogen (TN) were determined. Richness and H differed significantly among the sites. Principal component analysis consistently differentiated the soils in all 3 years. The P16 site did not differ in AAD from V0 and T26, while SOC and TN did not differentiate T26 from D40. Results showed a lower sensitivity of physical and chemical variables than CLPP to detect differences along the land use intensification gradient. Multiple correlations between Ri and H with AAD, SOC and TN (R > |0.70|), suggested a high association between the soil aggregation condition and organic matter content with microbial diversity.