Microbial 16S gene-based composition of a sorghum cropped rhizosphere soil under different fertilization managements

Driven by growing desertification and increases in the global demand for food, the necessity to adopt sustainable fertilization and crop management systems have greatly increased. In dryland soils, certain crops such as sorghum could provide important advantages. The impact of 3 years of N-fertilization with two rates of compost amendment on the composition of bacterial community of a Mediterranean soil cropped to sorghum was evaluated. The composition of bacterial communities of rhizospheric soil samples fertilized by urea (CT) or compost at single (COM1) or double doses (COM2), were compared to that of the bacterial communities from unfertilized rhizospheric soil (UF) and grassland soil (GS) by pyrosequencing. The highest number of sequences and OTUs were associated with rhizosphere soils treated with the double dose compost amendment (COM2), and analysis of alpha diversity clearly indicated a higher richness of this treated soil than other soils. Of the 16 bacterial phyla observed, Actinobacteria and Proteobacteria dominated. Actinobacteria abundance was higher in both compost-amended soils (COM1 and COM2) and GS than other investigated soils; Proteobacteria had the opposite trend. Significant differences (P < 0.05) were detected among class compositions of treatments. Most of the screened families belonged to α-Proteobacteria class. Species level analysis showed that GS and COM2-treated soil presented the highest percentage of unique OTUs; for 8 of the 14 most abundant OTUs, significant differences (P < 0.05) were found among soils. A clear distinction of bacterial communities of soil under different fertilization managements was observed from weighted as well as unweighted PCoA plots. Results from this in depth analysis clearly indicated that organic fertilization by compost, more than chemical fertilization by urea, can affect the composition of bacterial communities inhabiting the sorghum rhizosphere when compared to unfertilized soil and grassland soil.