Tree Species Mixtures Can Improve the Water Storage of the Litter–Soil Continuum in Subtropical Coniferous Plantations in China

Abstract

Increasing evidence has shown that introducing broadleaved trees into coniferous plantations can regulate hydrologic stores and fluxes; however, the effects and regulatory mechanisms of species mixing on the water conservation capacity of the litter–soil continuum remain poorly understood, and differences among tree species may appear. Herein, we investigated and compared the water conservation capacity of the litter layer (semi-decomposed and decomposed layer) and soil layer (0–100 cm) in a monoculture plantation (Pinus massoniana) and five mixed plantations (Pinus massoniana mixed with Cercidiphyllum japonicum, Manglietia chingii, Camellia oleifera, Michelia maudiae, and Bretschneidera sinensis) and comprehensively considered their potential influencing factors. We discovered that the identity of broadleaved tree species significantly affected the water storage of litter and soil in the mixed plantations (p < 0.05). The effective water-holding capacity of the litter (13.39 t·ha−1) was low due to the coniferous litter’s simple structure and challenging breakdown, despite the fact that the litter stock of the monoculture plantation was substantially larger than that of the mixed plantation (14.72 t·ha−1). Introducing deep-rooted tree species (e.g., Bretschneidera sinensis and Camellia oleifera) into Pinus massoniana farmsteads improved the soil-pore structure and aggregate stability, thereby significantly increasing the 0–100 cm soil water storage. Furthermore, we found that litter storage, soil organic carbon, and litter thickness, as key influencing factors, have complex effects on the water storage of the litter–soil continuum. Generally, these findings demonstrated that mixed plantations can potentially improve the water conservation capacity of the litter–soil system. Nevertheless, special attention should be given to the complementarity between tree species combinations.