In-depth insight into the short-term effect of floor management practice on young apple trees development and soil microbial biodiversity and activity.

Living mulches can be considered a practice providing multi-level benefits and several ecosystem services in orchards. Two multifunctional living mulches (Mix1 - Trifolium repens (20%) and Festuca ovina (80%), Mix2 - a mixture of 10 different species suitable as flowering strip) sown during the establishment of an apple orchard, were evaluated in relation to the impact on the soil nutrient content and bacterial microbiome, as well as the growth and yield potential of the apple trees. Notwithstanding the increase of N-nitrate and N-ammonia forms induced in the soil, both living mulches mixtures limited the growth and yield potential of the apple trees during the first two growing seasons. The two mixtures induced divergent effects on the biodiversity, activity and metabolic potential of the soil bacterial microbiome, not always increasing them compared to natural cover (control). Such effects could be related to modifications that both mixtures induced in the bacterial community capacity of metabolizing some classes of C-sources compared to control. This was particularly evident for Mix2 and in summer, when all classes of C-sources utilised by the bacterial community for its metabolism resulted to be significantly more exploited than in other seasons. In conclusion, the impact of very diverse living mulch mixtures on the growth, yield potential and overall nutrient status of the young apple trees could be related to modification of the tree physiological status, indirectly derived from the modifications observed on the soil bacterial communities' composition and metabolic capacity during the whole vegetative season. These results could provide hints for the correct soil management of the orchard to foster the exploitation of soil microbiome suitable for the apple trees development and production.