The planting of licorice increased soil microbial diversity and affected the growth and development of apple trees

Grass cultivation is an important soil management practice for improving orchard soil quality. A suitable grass variety can enhance the soil microenvironment and increase fruit yield and quality. In the arid regions of northwestern China, licorice is often planted between apple trees. To clarify the effects of licorice on the soil microenvironment and apple tree growth and development,apple trees and licorice were grown in a root limiter under the following three treatment conditions: apple alone (A), intercropping of apple and licorice (AL), and licorice alone (L). Several soil properties (e.g., salt, soil organic matter, nitrogen, phosphorus, and potassium contents) were analyzed. Additionally, soil microbial communities were characterized via the high-throughput sequencing of bacterial and fungal rRNA gene markers. Apple tree growth and development indices were also determined.The soil organic matter, total and available nitrogen, and the available phosphorus contents were significantly higher in the L treatment soil than in the original soil or the A and AL treatment soils. The compositions of the dominant bacteria and fungi were similar among treatments. Soil bacterial and fungal richness and diversity were greater for the L and AL treatments than for the A treatment. At the phylum level, the characteristic bacteria for the A and L treatments were Gemmatimonadetes and Chloroflexi species, respectively. Some soil properties, including soil organic matter, available N, available P, and available K contents, were significantly correlated with bacterial and fungal taxa. Furthermore, the apple tree growth and development indices trunk diameter, crown size, 1-year-old branch length, and the proportion of short shoots were respectively 25.66%, 21.70%, 28.23%, and 20.78% lower for the AL treatment than for the A treatment.Cultivating licorice alone or intercropping with apple trees can increase or maintain the soil organic matter, total and available nitrogen, and available phosphorus contents as well as the microbial composition and abundance. However, intercropping with licorice will restrict fruit tree growth and development (e.g., proportion of short shoots and the trunk diameter).