Understory shrub root systems and their exudates improve soil biochemistry in pine stands in temperate climate

The aim of our research was to determine how the addition of selected shrub species in single-species pine stands affects soil properties. We assumed that shrubs through roots and their exudates have a significant impact on the physicochemical and biological properties of soils. In our research, we took into account four study plots variants: a single-species pine stand, a pine stand with an admixture of rowan, a pine stand with an admixture of alder buckthorn and pine stand with an admixture of European hazelnut. In our research, we focused on determining the role of the root systems of selected shrub species in shaping soil properties. We determined the morphological features of the roots, their increment as well as we analyzed the amount of carbon released with their exudates. We used extracellular and intracellular enzyme activity and microbial biomass to assess biochemical status of soil. Our research indicates the significant impact of the morphological features of roots and their exudates on shaping the enzymatic activity of the tested soils. Multiple regression analysis indicates the importance of root increase, SRA and the number of tips in shaping enzymatic activity. At the same time the strong correlations were noted between the activity of extracellular and intracellular enzymes and root exudates. European hazelnut secreted the most C regardless of the sampling date. Shrubs in pine monocultures create fertile islands, determined by more favourable soil properties, which is consequently important for soil health. Our results indicate that shrubs can be valuable element of the forest ecosystem, which has a positive effect on soil properties, and as a consequence which may improve the stability of forest stands.