Effect of Eucalyptus and Precious Tree Species Mixed Forest on Soil Physicochemical Properties and Microbial Biomass

In order to evaluate the improvement effect of Eucalyptus and precious tree species mixed forest on soil quality and screen the optimal configuration, this study selected Eucalyptus pure forest and Eucalyptus×Parashorea chinensis H. Wang, Eucalyptus×Michelia odora, Eucalyptus×Erythrophleum fordii mixed forest as the research object, collected soil samples in 0～20 cm and 20～40 cm soil layers, and explored the differences and correlations of soil physical and chemical properties and microbial biomass in different mixed stands. The results were as follows:(1) The soil bulk density of the three mixed forests decreased in both soil layers, and the water holding capacity and porosity indexes increased significantly. Among them, eucalyptus×Michelia odora is the best in deep soil.(2) In the two soil layers, the soil nutrient content of the three mixed forests was significantly higher than that of the pure forest. The mixed stands of Eucalyptus×Parashorea chinensis H. Wang and Eucalyptus×Michelia odora had the best effect in improving organic carbon, pH value, phosphorus and potassium, and the mixed stands of Eucalyptus×Erythrophleum fordii had the best effect in improving total nitrogen.(3) The contents of MBN and MBP in the two soil layers of Eucalyptus×Parashorea chinensis H. Wang and Eucalyptus×Michelia odora mixed stands were significantly higher than those in the other stands.(4) The MBC/MBN values of Eucalyptus×Parashorea chinensis H. Wang, and Eucalyptus×Tsoongiodendron odorum mixed forests were relatively low.(5) There was a significant positive correlation between microbial biomass and soil nutrient indexes. Only MBP had a significant positive correlation with soil water holding capacity, and MBC/MBN had a significant negative correlation with capillary porosity. In conclusion, the mixed stands of Eucalyptus with Parashorea chinensis H. Wang and Michelia odora could comprehensively improve the soil quality through a synergistic approach of optimizing the physical structure of the soil, enhancing the availability of nutrients and increasing the activity of microorganisms.