The effect of pyrogenically modified substrates on mineralizing activity and growth strategies of microorganisms of grey forest soil

Abstract

The rates of the mineralization processes initiated by the input of plant residues and pyrogenically modified plant material into gray forest soil under forests and meadows were assayed. While meadow plant residues was mineralized more rapidly than the forest floor, decomposition of the pyrogenic material resulted in disproportional changes in CO2 emission from soils. Statistical treatment showed that the respiratory activity of CO2 emission by heterotrophic microorganisms, which is a physiological characteristic of microbial communities, is 89% determined by the substrate quality. The maximal specific growth rate, which reflects the functional changes in microbial communities, was affected by the cenosis (36%) and the substrate (30%). Most of the carbon of the original plant material (up to 90%) was removed during the burning of plant substrates. The remaining compounds in the pyrogenically transformed material changed the process of mineralization in soil compared both to the control variant and to soil enriched with plant residues. Input of plant residues and ash into the soil resulted in increased total and active biomass, while the maximal specific growth rate decreased and the generation time for the active biomass increased. In the case of soils with plant residues, these changes in the state of microbial communities were brief and occurred during the period of intense mineralization (0–5 days), while, in soils with plant ash, stable changes were revealed after more prolonged incubation. Experimental determination of the microbial biomass turnover time (MTT) by means of two methods (from the ratio between the microbial biomass and respiration and from microbial specific growth rates) made it possible to determine the economical coefficient Y for microbial communities metabolizing the substrates of different availability. Depending on the experimental variant, the Y values varied from 0.22 to 0.51. Decreased maximal specific growth rate and increased values of Y (the coefficient of efficiency of substrate utilization) showed the predominant contribution of K-strategists in the mineralization of low available substrates in soil. The balance calculations and physiological characteristics of the microbial community suggested that the priming effect was most probable in soils enriched with plant ash.