Influence of Tree Species Composition on Leaf and Soil Properties and Soil Enzyme Activity in Mixed and Pure Oak (Quercus variabilis) Stands

There is an increasing number of studies providing evidence that multi-species tree plantations possess more advantages in terms of species-specific tree diameter, growth rates, and soil properties than monocultures. In order to clarify the effect of a multi-species tree plantation on leaf nutrition and soil fertility, a statistical analysis was carried out on the leaf and soil properties, as well as soil enzyme activity, from two repeatedly measured stands in the Qingliangsi Forest District of the Dengfeng Forest Station. For the analysis, the plots were categorized into type A and type B according to the different forest structures. Type A was the mixed plantation of Quercus variabilis and Platycladus orientalis, while type B was a pure stand of Quercus variabilis. The results clearly showed that the leaf water content of P. orientalis was greater than that of Q. variabilis. The total water, free fatty acids, soluble sugar, flavonoid, tannin, lignin, cellulose, and hemicellulose contents of P. orientalis were higher than those of Q. variabilis in type A. Furthermore, the soil moisture of the mixed plantations was apparently higher than that of the pure stand. Soil peroxidase activity was the highest both in type A and type B among the 10 soil enzyme activities. Meanwhile, there was a significant difference between soil catalase and acid phosphatase activities. Soil urease, leucine aminopeptidase, and sucrase were significantly correlated with multiple soil enzyme activities. In addition, based on the correlation analysis results, we noted that type A had more complex relationships than type B in the leaf and soil properties and soil enzyme activity. Compared to the monoculture stands, multi-species tree stands appeared to have more complicated and preferable soil and water conservation capabilities. These results further verify the beneficial role of mixed plantations in water holding capacity and in improving soil quality. Q. variabilis is a broad-leaved deciduous tree species, and P. orientalis is an evergreen coniferous tree species. Our study indicates that these two native Chinese tree species are suitable as the target species when constructing mixed forests. They can increase the interaction of leaf and soil properties, enhance the soil enzyme activities, and improve the soil.