The Effects of Nutrient and Water Use Efficiency on Plant Species Diversity in the Understory of Broad-Leaved Evergreen Forests

The factors driving plant species diversity in different forest types and layers are still insufficiently understood. Therefore, we investigated the limiting factors of nutrient and water use efficiency in three forest layers (arbor, shrub and herb layers) and two forest types (plantation forest and natural forest), as well as their potential relationship with plant species diversity. The study area is located in mid-latitude evergreen broad-leaved forest ecosystems in southern Anhui province. The nitrogen content in the soil (2.90 g kg(-1)) exceeded the national average for forest ecosystems (1.06 g kg(-1)), whereas the phosphorus content (0.43 g kg(-1)) was below the national average for such ecosystems (0.65 g kg(-1)). The plant species diversity in the arbor layer was comparatively low, and nitrogen exerted a more substantial influence on it. In contrast, phosphorus had the most significant impact on the shrub and herb layers. In conclusion, nitrogen has little effect on plant growth patterns in this area, while there is a potential role for phosphorus in regulating plant succession rates. There are phenomenon of excessive nitrogen deposition and phosphorus loss in this forest ecosystem. Despite the fact that the plant species diversity indices (the Pielou Evenness Index, Gleason Richness Index, Shannon-Wiener Diversity Index and Simpson Dominance Index) in natural forests were higher than that in plantation forests, the disparity between them was not significant (p > 0.05). This may be due to similar water use efficiency and climate. The findings of this research hold substantial significance for forecasting the alterations in plant species diversity, functionality, and their influencing factors within mid-latitude evergreen broad-leaved forests.