Objectives  The aims were to investigate the responses of orchard soil organic carbon (C) pool and biochemical properties to the combined application of wheat straw and different cellulose degrading bacteria strains.

  Methods  The typical alkaline soil in the north of Henan Province were collected as the research object. The treatments included control (CK), wheat straw alone application (S), wheat straw applications with Bacillus nealsonii (S + B), Cohnella (S + C) and Paenibacillus lautus (S + P). The organic C contents, enzyme activities, available nutrients and salinity properties were analyzed using a laboratory experiment.

  Results  The rates of organic C mineralization were increased firstly and then reduced during incubation 100 days, which fitted with the first order dynamics model. Wheat straw applications with the three kinds of cellulose degrading bacteria increased the rates of organic C mineralization, cumulative of C mineralization and potentially mineralized C contents, compared with S treatment. The contents of soil organic C, microbial biomass C, dissolved organic C and readily oxidized organic C were markedly increased in S + B treatment, which was 10.1%, 35.5%, 26.3% and 24.3% higher than that in S treatment, respectively. Wheat straw application with the cellulose degrading bacteria enhanced the C management index and the soil enzyme activities. The cellulase, alkaline phosphatase and dehydrogenase activities in S + B were markedly higher than S treatment. Compared with wheat straw alone, the wheat straw application with cellulose degrading bacteria increased the contents of available nitrogen, phosphorus, potassium and exchangeable Mg^{2 +} , while reduced the pH value and exchangeable Ca^{2 +} content. Soil available nitrogen, phosphorus and microbial biomass C were the major factors that regulated the mineralization of organic C.

  Conclusions  Wheat straw application with cellulose degrading bacteria markedly increase the activity and content of soil organic C, and improve biochemical properties of alkaline soil in orchard, especially in the S + B treatment.