Biological activity and microbial genetic diversity of bare-fallow and grassland soils

Abstract

Microorganisms and their interactions with plant and soil provide soil environment integrity. The structural and functional diversity of microbial population in soil is necessary to maintain resistance to environmental perturbations. The aim of this study was to compare metabolic activity and genetic diversity of soil microbial communities at different depths under two soil managements. The experiment included five following soil objects: GR20 – rhizosphere from grassland (0–20 cm), GNR20 – nonrhizosphere grassland (0–20 cm), GNR40 – nonrhizosphere grassland (30–40 cm), BF20 – bare fallow (0–20 cm), BF40 – bare fallow (30–40 cm). Metabolic activity was assessed by dehydrogenases activity and community level physiological profiling using EcoPlates. The study also included genetic diversity assessment, with the use of denaturing gradient gel electrophoresis to reveal genetic structure of ammonia-oxidizing bacteria (AOB). The results showed that soil metabolic and biological activity decreased with soil depth and decreased in bare fallow objects. Highly utilized substrates in both management systems belonged to compounds of microbial biomass. These microbial substrates were amino acids, especially l-asparagine, and fungal substrates were mannitol and N-acetyl-d-glucosamine. In grassland soil highly degraded substrates additionally included d-cellobiose and d-xylose, which are compounds of plant cell walls. Analysis of genetic differentiation among treatments showed unique AOB structure in soil rhizosphere. This was mainly caused by the availability of roots exudates, including amino acids and carbohydrates.