Spatial Distribution Characteristics of Root Systems in Different Configuration Patterns of Tilia miqueliana and Hibiscus syriacus

Purpose To explore the increasing mechanism of the species and number diversity of shrubs under arbor forest, and to construct a stable plant community by the difference of underground spatial niche and the growth complement between root systems.

Methods Three arbor-shrub configuration patterns were established within a Tilia miqueliana plantation by underplanting Hibiscus syriacus at different densities: 1 m×1 m (pattern 1), 2 m×2 m (pattern 2), and 3 m×3 m (pattern 3). The spatial distribution and number of T. miqueliana roots were measured by tree radar unit. The distribution range of H. syriacus roots was determined by the whole-root excavation method, and was classified and counted by coarse roots (> 2 cm), medium roots (1.0-2.0 cm) and fine roots (0.5-1.0 cm).

Results The root system of T. miqueliana was characterized as a vertical type, with straight and deep taproots, fewer lateral roots, concentrated in the area within 3 m from the trunk and the soil depth >60 cm, accounting for 35.17% of the total root system. The root system of H. syriacus was horizontally distributed, with more horizontal roots and fibrous roots, which are distributed in a shallow layer, concentrated in the top 0-20 cm soil layer within a 1 m radius. All T. miqueliana-H. syriacus configurations altered the original spatial distribution of root systems, and the interaction was manifested as pattern 2>pattern 1>pattern 3. In patterns 1 and 2, the root number of T. miqueliana decreased in the 0-30 cm soil layer at a distance of 1-2 m from the trunk, but increased in the 30-60 cm layer. In pattern 1, the roots of H. syriacus showed predominantly vertical growth with evenly distributed lateral roots. In pattern 2, the roots of H. syriacus increased the growth amount in the horizontal and vertical directions, and the total length of the root system was higher than that in patterns 1 and 3.

Conclusion The spatial distribution of root systems in the T. miqueliana-H. syriacus configuration is reasonable, with a niche overlap of only 5.9%-13.5%. 2 m×2 m (pattern 2) is considered the optimal configuration, exhibiting significant interspecific facilitation and strong community root system stability.