Effect of long-term radish (Raphanus sativus var. sativus) monoculture practice on physiological variability of microorganisms in cultivated soil.

Long-term monoculture may affect soil environment biodiversity. An example of such a plant is radish (Raphanus sativus var. sativus), an economically important crop in Poland, a quick-growing vegetable with intensified harvest throughout the season. The aim of this study was to determine changes in biodiversity of soil under radish cultivation and to compare the research methods applied. The monoculture practice affected soil pH, but the organic carbon content remained stable. 16S RNA-seq analysis revealed changes in soil microbial population, with the dominant phyla Proteobacteria (37.3%), Acidobacteria (19%), and Actinobacteria (16%), and the dominant taxa Gaiella (1.59%), Devosia (1.51%) and Nocardioides (1.43%). These changes have not fully expressed in the number of culturable microorganisms, where only fungal abundance changed significantly. However, the physiological state of microbial cells (λ) indicated that oligotrophs and copiotrophs were in a vegetative (λ > 3.0) state at the beginning of the season and fungi at the end of the year. Changes in the biodiversity of soil microorganisms were visualised using Community Level Physiological Profiling, where an oscillation in Average Well Colour Development (OD = 0.78-1.48) was observed in successive months of radish culture, with biodiversity indices (Shannon and Substance richness) remaining similar. The greatest variation in the influence of monoculture practice on soil factors was observed for the soil enzymes activities (for dehydrogenase and peroxidase activities - 0.5 μg TPF/h/g DW and 1.5 μmolPYGL/h/g DW respectively). Alkaline phosphatases predominated among this group of enzymes, and the activity of carbon metabolism enzymes decreased over the season, except for invertases, where an increase in activity of up to 50 μg Glc/h/g DW was observed. All the parameters studied indicated changes in the soil environment. Nevertheless the microbial community remains stable during the whole experiment returning to equilibrium in a quite short time after changing conditions.