Metabolic and genetic patterns of soil microbial communities in response to different amendments under organic farming system

In the organic farming system plant production mostly depends on the decomposition of soil organic matter through the activity of the microbial biomass, which is able to provide significant quantities of essential nutrients for plant growth. The aim of this work was to compare the persistence of microbial heterotrophic metabolism along decimal dilutions of soil treated with different organic amendments, by using Biolog EcoPlate™. The amount of the different amendments was adjusted in order to meet the N requirement of tomato crop. The Biolog results were used to draw a binomial matrix of data by setting all the positive results to 1 and all the negative results to 0. The occurrence of the microbial oxidation of each Biolog Ecoplates™ C source was calculated as probability ‘p’ on the binomial set of data for each dilution. In terms of persistence of C sources utilization by soil microflora, along decimal soil dilutions, the treatments can be roughly divided in 3 different categories: the worst performing (control), the intermediate performing (biochar), and the best performing (biochar added to an organic fertilizer, the organic fertilizer alone and 3 composts). Biolog positive wells at the dilution 10− 4 were used to carry out a molecular characterization of bacterial communities by 16S fingerprinting, through the H′ Shannon diversity index. Microbial communities utilizing cellulose and hemicelluloses as C source changed their species composition in response to the different amendments. In particular, amendments with biochar, regardless of the application of organic fertilizers, brought to the highest diversity of cellulose degrading bacteria.