Visualization of soil microbial processes with a light microscope. Part 1. The ratio of fungi and bacteria in microbial landscapes as an indicator of the state of soil organic matter

The aim of the study is to investigate location features of fungi and bacteria on glass slides exposed to arable and virgin soils. Location and time of the study. The studies were carried out in 2018-2021. Objects of study: 1. Leached chernozem (Luvic Chernozem, the forest-steppe of the Ob region, 54° 53' 13.5 "N and 82° 59' 36.7" E). Observation options: (1) permanent steam field (300 mg mortmass C/kg, 50 mg N-NO3/kg); (2) wheat cultivation, annual removal of straw from the field + bare fallow (440, 10); (3) long-term fallow field (virgin soil; 2500, 0). 2. A complex of permafrost alas soils (Cryosols) of varying degrees of pasture digression (Lena-Amga interfluve, 62° 33' 24.3" N and 130° 54' 01.4" E). Methodology. The duration of glass slide exposure in field conditions ranged from a growing season to a year. To decipher landscapes obtained in the field, glass slides were exposed in laboratory conditions in samples of the same soils with disturbed and undisturbed (monolith) structure. To study microbial succession during decomposition of plant residues 30-60 days incubation experiments were carried out. In some cases, to obtain a microbial imprint of decomposition of organic matter, glass slides were previously wrapped in cotton cloth. After exposure, the glass slides were dried, fixed, stained with carbolic erythrosine (5%), and examined microscopically at magnification of ×40-×1000. We studied 50 fields of vision on one glass slide (3 slides on each variant). The snapshots were taken using Primo Star Zeiss microscope with an Axiocam 105 color video camera. Results. The size and localization of bacterial cells on a microbial landscape depend on the amount and state of soil organic matter. We outline a schematic representation of change in the fungi to bacteria ratio in landscapes during decomposition of plant residues. In contrast to arable soil, in virgin soil a bacterial biofilm was formed on the surface of hyphae. Conclusions. A visual series of microbial succession during the decomposition of plant residues in arable and virgin soils is presented. The bacterial biofilm formation on the surface of hyphae might indicate stability of soil microbial system