In this study, we investigated the effects of natural grass growth on the physical properties of soil and microbial diversity in a pear orchard located in the yellow river delta. The soil properties and microbe diversity in orchards containing grass grown for 4, 6, and 9 years respectively, was characterized and compared with those in soil from orchards that did not have grass growth, which served as the control in this experiment. The results showed that multiple years of grass growing significantly enhanced soil porosity and reduced soil bulk density and conductivity, suggesting that permitting growth of natural grass in the orchard could reduce soluble salts in soil, without an influence on water content in the soil. Grass growth also increased the microbial mass C and N. By employing PCR-DGGE and sequencing technology, we found that the majority of the increased bacteria were species that could not be cultured. In comparison with control, the microbial respiration and activity, and the global phospholipid fatty acid concentration was increased after several years of grass growth, although the phospholipid fatty acid varieties were not affected, and no significant differences were found among treatments. Meanwhile, grass growth also improved carbon utilization capacity, with the most significant effect being displayed after 4 years implementation, and the more balanced utilization of six carbons were simultaneously achieved during this process.
In summary, our study shows that the culture of naturally grown grass in the orchard significantly increases microbial biomass C, N, and microbe diversity, and that uncultured species constitute the major part of the increased bacterial concentration. Moreover, sustained grass culture in the orchard benefits the up-regulation of soil microbial activity and respiration and the increasing amount of active microbes and total phospholipid fatty acids. It is also effective at stimulating the balanced utilization of six carbons by microbes.