Microbial biomass, metabolic activity and nutritional status determined from fatty acid patterns and poly-hydroxybutyrate in agriculturally-managed soils

Abstract

Soil microbial biomass, fatty acid pattern, poly-β-hydroxybutyrate content and selected physiological variables were studied in agriculturally-managed soils with different cropping histories: crop rotation, hops and grassland. Significant correlation was observed between substrate-induced respiration, the amounts of adenine nucleotides and the total amounts of phospholipid fatty acids. The highest microbial biomass was found in a grassland soil, the lowest in soils which were formerly cultivated with hops. Additionally, the highest ratio of poly-β-hydroxybutyrate: total phospholipid fatty acids, the largest specific respiration rate and the lowest amounts of the adenylate energy charge were obtained in one of the former hop yards. Due to the frequent treatment of hop plants with fungicides a large amount of copper had accumulated in this former hop yard. The condition of the soil had resulted in the creation of a microbial community with markedly different biochemical characteristics compared to communities associated with grassland soil or crop rotation soil. The principal component analysis was able to discriminate the different soils when applied to hydroxy fatty acids. The profile of fatty acids in the copper-contaminated soil indicated an increase in numbers of Gram-negative bacteria. A lower concentration of branched chain fatty acids revealed a decreased proportion of Gram-positive bacteria in both former hop yard soils.