Effect of biochar on extracellular enzyme activity and microbiome dynamics across coarse sandy soil depths

The aim was to assess the effect of straw biochar on microbiomes along the depth (30-80 cm) of two coarse sandy subsoils. We hypothesized that biochar modifies extracellular enzyme activities (EEA), and diversity and structure of microbiomes across the subsoil depths. Two subsoils were amended with straw biochar (0%-4% w/w) and incubated for 16 months in a column experiment with two cultivations of spring barley. EEA were assessed using fluorogenic assays, while the prokaryotic and fungal communities were analyzed via 16S rRNA gene and ITS2 amplicon sequencing, respectively. Biochar significantly increased water holding capacity and pH. It also significantly decreased the phosphomonoesterase activity, suggesting enhanced soil phosphate bioavailability. In both subsoils, biochar significantly increased the prokaryotic α-diversity index. Biochar impacted prokaryotic community structures more than fungal community structures. Prokaryotic community structures were significantly different with increasing biochar content at deeper soil depths. Moreover, in both subsoils, biochar significantly increased the relative abundance of a prokaryotic consortium. We conclude that the biochar-induced improvements in physicochemical soil properties stimulate microbial diversity and functional activity across varying depths in coarse sandy subsoils. These findings are valuable for assessing the potential benefits of biochar application on agricultural subsoil health.