Water Conservation Capacity of Soil and Litter Layers of Five Magnoliaceae Plants in Hainan Island, China

Magnoliaceae plants have high ornamental value, resulting in their widespread use in landscaping construction, and play a major role in the ecological functions of soil and water conservation. However, the landscape value of magnolias from the perspective of the water conservation capacity of the litter and soil layers is not yet fully understood; this restricts the popularization and application of Magnoliaceae plants in landscaping. In this study, we determined the characteristics of the litter thickness and mass, water absorption process, and soil water-holding capacity associated with five Magnoliaceae plants (Michelia shiluensis, M. crassipes, M. foveolata, M. maudiae, and M. odora). (1) The total litter thickness ranged from 2.29 to 5.58 cm, with M. crassipes achieving the highest value. The total litter mass for M. shiluensis (25.11 ± 2.58 t·ha−1) was largely greater than that for the other magnolias. The mass of the un-decomposed litter (UL) layer was 1.31- to 3.82-fold larger than that of the semi-decomposed litter (SL). (2) The maximum water retention capacity (Hmax) and effective water retention capacity (Heff) of M. shiluensis were markedly larger than those of the other magnolias. (3) The Wmax and Weff of the UL layer were greater than those of the SL layer. (4) The soil bulk density varied from approximately 1.22 ± 0.08 g·cm−3 to 1.55 ± 0.08 g·cm−3, and the total soil porosity varied from 40.03 ± 3.44% to 46.42 ± 1.02%. The soil bulk density rose with an increasing soil depth, yet the total porosity was reduced. The soil water-holding capacity of the 0–30 cm soil layer varied from approximately 26.23 to 70.33 t·ha−1, with soil near M. crassipes having the greatest water-holding capacity. The soil water infiltration recorded for M. crassipes was significantly higher than that of the other magnolias. The water conservation capacities associated with M. crassipes and M. shiluensis were the largest, which may suggest that these species are better at increasing rainfall interception, lightening splash erosion, and reducing surface runoff. Hence, we suggest that M. crassipes and M. shiluensis should be prioritized in landscaping applications.