This is the data analysis R script for the microbial dataset for the publication (in prep) "Tripled Plant Productivity and Soil Microbiome Restructuring through Volcanic Ash Fertilization in a Greenhouse Experiment" by Hubert Staudigel, Mathilde Borg Dahl, Yohannes B. Tesfay, Ilka Beil, Tim Urich, Juergen Kreyling. Abstract Volcanic ash is widely held responsible for fertile soils but the processes and conditions leading to volcanic soil fertility remain poorly understood. We report here the results of a greenhouse Volcanic Ash Fertilization (VAF) experiment aimed to explore the relationships between basaltic ash addition (0-10 wt%) to soil, and its impact on plant growth, nutrient uptake and the soil microbiome. Our four-month experiment with Plectranthus scutellarioides clones on forest soil revealed a non-linear growth response with distinct growth patterns below and above 3 wt% ash addition, respectively. Low ash VAF ( 3 wt% ash concentrations, with no apparent further change with increasing ash content. Key changes were an increased relative abundance of several potentially plant-growth-promoting rhizobacteria and fungi, but also a decreased nematode abundance, suggesting that changes in the microbiome are likely a major factor for the substantial VAF effect observed in our experiment. We show here that (1) VAF of basaltic ash is an effective mechanism for enhancing plant growth, albeit not a simple ash-nutrient to plant transfer as commonly assumed and (2) the impact of VAF on global biomass production may be a candidate process enhancing atmospheric CO2 sequestration. Description of the data and file structure It is a walk through of the Bioinformatic steps of the DADA2 pipeline, followed by the R codes for statistical analysis and plotting of the data.