Abstract: To understand the variation of bacterial communities in soils of walnut orchard with different planting years, we measured soil bacterial community diversity and carbon source metabolism function in the surface (0-20 cm) and subsurface (20-40 cm) layers of walnut orchard with different planting years (1-3, 5, 8-10, 15 and 20-25 years) by using highthroughputsequencing and Biolog ECO microplate. The correlations between diversities of bacterial community〖JP〗 and carbon source metabolism function with soil physicochemical properties were analyzed. The results of highthroughput sequencing showed that bacterial communities showed surface accumulation in soils. After five years of planting, the number of OTUs and diversity indices in surface layer were higher than that in subsurface layer. Proteobacteria, Acidobacteria, Actinomycetes, and Chloroflexi were the dominant bacteria phyla. With the extension of planting years, the relative abundance in different soil layers showed a tendency of increasing first and then decreasing. The relative abundance of clearly classified dominant genera in soil of 10 years planting was the highest. Biolog analysis results showed that bacterial activities in the surface layer were significantly lower than those in the subsurface layer. With the extension of planting years, bacterial activities and Shannon diversity index increased first and then decreased. Orchard with 8-10 years and 15 years planting history had the highest bacterial metabolic activities and diversities. The utilization of amino acids and polymers by surface soil bacteria increased gradually, while the utilization of other carbon sources increased first and then decreased. In subsurface layer, the utilization of all carbon sources decreased except phenolic acids. There were negative correlations between Shannon diversity index and physicochemical properties of surface layer, and positive correlations between Simpson diversity index and physicochemical properties. Total salt content, pH and nutrients were the main factors affecting the bacterial diversities of surface layer. The diversities of bacterial community and utilization of carbon sources in different soil layers of walnut orchard with planting for 1-3 years and 20-25 years were obviously low, which exacerbated the imbalance of soil microenvironment. Manures or biofertilizers should be added to improve soil microenvironment of walnut orchards.

Key words: planting years, walnut orchard, soil bacterial community diversity, high-throughput sequencing, Biolog.