Influence of biochar on the taxonomic composition and structure of prokaryotic communities in agro soddy-podzolic soil

Abstract

Currently the scientific literature is actively discussing the feasibility of biochar using in agriculture. Biochar is one of the new types of organic meliorants. It is obtained by pyrolysis of wood or other plant waste in an inert atmosphere converting carbon compounds to a stable state. Its use is recommended to increase the soils biological activity and the agricultural crops productivity and it is actively implement in agricultural technologies of foreign countries. However many aspects of the biochar influence on the agrocenoses properties and state have been poorly studied. There is information about both positive and negative processes occuring in soils under biochar. The main concern is the data on the biochar influence on humus mineralization, since dehumification can lead to loss of soil fertility and ecological stability. This is especially important for soddy-podzolic soils characterized by a low humus content and a weak degree of humification. Such soils initially have low ecological stability and are quite vulnerable to human impact. Therefore using soddy-podzolic soils in agriculture considerable attention should be paid to the microbiological and biochemical transformation of soil organic matter. Studies on the biochar influence on the soil microbiota composition and state in our country are isolated, and for soddy-podzolic soils of the North-Western region of Russia are conducted for the first time. The aim of this work was to assess the influence of biochar on the features of the agro soddy-podzolic soils prokaryotic community. The research was carried out in incubation experiments on well-cultivated agro soddy-podzolic sandy loam soil of the Leningrad region. The biochar was produced by fast pyrolysis of birch and aspen wood at 550 °C. Its concentration in the experiment was 1%. The incubation time was 7 and 90 days. The repeat of the variants of the experiment was 3-fold. The content of total organic carbon and nitrogen, mineral forms of nitrogen, and soil suspension pH were determined in soil samples using methods commonly used in agrochemical practice. The method of sequencing the variable region of the 16S rRNA gene was used to determine the taxonomic composition of soil prokaryotes. The sequence clustering and the taxonomic identification of the taxonomic units (OTU, Operational Taxonomic Unit) were performed using the QIIME program. The diversity and evenness of agro soddy-podzolic soil bacterial communities was estimated by the OTU number and Shannon index. Statistical data processing was performed using IBM SPSS Statistics, Version 25 (IBM, USA). The reliability of the differences between the variants was measured by one-factor variance analysis using the Duncan's or Student-Newman-Keuls test at p < 0.05. The intensification of the processes of mineralization of soil organic matter occurred under biochar. The humus content in the soil decreased from 4.41 to 3.83 % which is 11 % more than in the control during the observation period. Activation of organic matter transformation processes took place simultaneously with changes in the state of the prokaryotic community. This community was represented mainly by the bacteria phyla Actinobacteria, Firmicutes, Proteobacteria, Chloroflexi, Acido bacteria, Planctomycetes, Verrucomicrobia. The biochar application was accompanied by an increase in the total bacteria diversity and by the abundance of phyla Planctomycetes, Verrucomicrobia, Proteobacteria and FBP representatives but also by a decrease in the abundance of phyla Actinobacteria, Nitrospirae, Firmicutes and Fibrobacteres representatives. In general biochar application leads to increase in the oligotrophs abundance and to reduce the copiotrophic proportion in prokaryotic community. The inhibition of bacteria from phylum Nitrospirae can be explained by a decrease in the concentration of available ammonium. In addition biochar application leads to increase in the abundance of some taxa containing active hydrolytics of natural polymers (orders Myxococcales and Xanthomonadales, class Sphingobacteriia etc.). Most likely this is due to the intensification of the difficult mobilizing organic substances transformation in agro soddy-podzolic soils under biochar.