Endospores, prokaryotes, and microbial indicators in arable soils from three long-term experiments

摘要

Management impacts on microbial communities in arable soil may influence soil quality and fertility. We examined the composition of the prokaryotic community in soils maintained under specific treatments for 24-118 years at Askov Experimental Station, Denmark. The experiments involved nutrient addition (unfertilized, mineral fertilizer, cattle manure), straw disposal (no straw, 8 t straw ha(-1) year(-1)), and soil texture (5-18 clay). Domain- and phylum-assigned cells were quantified by 16S ribosomal RNA (rRNA) gene analysis and endospores by analysis of dipicolinic acid (DPA). Amino sugars (glucosamine, galactosamine, and muramic acid) were assayed as microbial source indicators. Severe nutrient depletion reduced cell numbers and increased endospore abundance; straw disposal slightly increased both prokaryote and endospore numbers. Nutrient source (animal manure or mineral fertilizer) and soil texture had a little effect on cell and endospore numbers. With the notable exception of unfertilized soil, the ratio of endospores to total cells was similar across all treatments. The 16S rRNA gene analysis showed dominance of Bacteria over Archaea, the latter accounting for 0.2-8.4 of total genes. Archaeal abundance differed a little among treatments. Firmicutes made up 0.2-1.2 of the bacterial 16S rRNA genes. The numbers of Firmicutes were lower in unfertilized than in fertilized soil and decreased with decreasing soil clay content; straw treatment and nutrient source had a little effect. Amino sugar ratios suggested a dominance of fungi over bacteria, but the concentrations of microbial indicators and soil organic C were closely correlated, indicating that the amino sugar ratios represented a historical fingerprint (legacy effect) of the impact of management on the microbial community. Our results show that it takes extreme management to distort the general structure of prokaryotic communities in temperate arable soils.