Abstract:Understory plant diversity and soil physicochemical properties are the key indicators of soil and water conservation stability and growth ability. Five typical stand types on Pingtan Island were selected, including Acacia confusa forest (I), Pinus thunbergii forest (II), A. confusa + Casuarina equisetifolia forest (III), P. thunbergii + A. confusa forest (IV) and P. thunbergii + Eurya emarginata forest (V), the differences of understory plant diversity and soil physicochemical properties in different stand types were analyzed, and explored their relationships through redundancy analysis (RDA). The results showed that the mixed forest of P. thunbergii + A. confusa was more beneficial to enrich the species diversity in the understory, while the community structure of A. confuse + C. equisetifolia forest was simple with low species diversity. The soil physicochemical properties of different mixed forests were different. Compared with pure forest, the mixed planting of tree species was beneficial to increase the total potassium content of soil, and A. confuse + C. equisetifolia and P. thunbergii + E. emarginata forest were beneficial to enhance soil organic matter content, total nitrogen, alkali-hydrolytic nitrogen and available phosphorus. Soil total K and water soluble salt had the greatest influence on species diversity in understory, and total K was negatively correlated with species diversity index in shrub layer and herbaceous layer. The total water soluble salt was positively correlated with the species diversity index of shrub layer and negatively correlated with the species diversity index of herbaceous layer. Therefore, in order to improve the species diversity of the understory, the mixed planting of P. thunbergii + A. confusa could be considered. To improve soil fertility, mixed planting of A. confusa + Casuarina equisetifolia, P. thunbergii + A. confuse could be considered. At the same time, tree species coordination was carried out through artificial tending, thinning and replanting, so as to reduce allelopathy of Casuarina equisetifolia, control total potassium and water soluble salt content in soil for promote long-term stable development of community.
