Enzyme Activity and Dissolved Organic Carbon Content in Soils Amended with Different Types of Biochar and Exogenous Organic Matter

Biochars are proposed as a strategy for long-term carbon sequestration. High resistance for decomposition, low decay rate and long estimated lifetime allow for stable forms of carbon to be retained in the environment. Nevertheless, the application of pyrolyzed feedstock, particularly along with exogenous organic matter, may affect carbon dynamics in soil through the introduction of labile compounds and the stimulation of extracellular enzymes. The aim of this research was to evaluate the influence of biochars and unprocessed organic amendments in two agricultural soils on the dissolved organic carbon (DOC) content and activity of three enzymes involved in carbon turnover. In the incubation experiment, the activity of dehydrogenase, beta-glucosidase, and cellulase and the DOC content were measured on days 30, 60, 90, 180, and 360. The addition of biochars stimulated dehydrogenase and beta-glucosidase, while cellulase was suppressed. Fresh biomass enhanced the activity of the enzymes through a priming effect. DOC content was the highest in treatments with high enzyme activity, suggesting that it acted as a source of energy for microbes. The findings suggest that the biochar properties and the presence of exogenous organic matter affect microbial response in soil, which might be crucial for carbon sequestration. However, long-term studies are recommended to fully understand the mechanisms that determine the response of soil biota to biochar.