Effects of different rotation periods of Eucalyptus plantations on soil physiochemical properties, enzyme activities, microbial biomass and microbial community structure and diversity

Eucalyptus is widely cultivated in southern China as a short-rotation fast-growing species for timber production. However, this kind of business model has aroused widespread concern on soil quality. This study aimed to determine the cutting period of Eucalyptus plantation by comparing the effects of different cultivation years on soil quality. Four Eucalyptus stands, including 2-, 6-, 10-, and 15-year-old (abbreviated as 2 yr, 6 yr, 10 yr, and 15 yr, respectively) were used, and 25 soil physicochemical and biological indicators were determined. Results showed that the soil texture of the 10 yr and 15 yr plantations significantly improved. Soil organic matter, macronutrients, enzyme activity, and microbial biomass decreased significantly at 6 yr and then increased at 10 yr. However, the contents of available nutrients and the activities of urease and catalase decreased again at 15 yr. Redundancy analysis showed that the contents of total phosphorus, available phosphorus, available potassium, available zinc, and available calcium considerably influenced the soil bacterial community, whereas the contents of total nitrogen and available nitrogen greatly affected the fungal community. Meanwhile, pH and soil texture exerted a significant impact on microbial community structure. Bacterial diversity showed an increasing trend with the rotation period, whereas the fungal diversity ranked by 2 yr > 6 yr < 10 yr > 15 yr. The relative abundances of soil major microbial taxa were closely related to the soil physicochemical properties and were roughly similar to ecological strategy. These results suggest that cultivation period significantly affected the soil quality. Thus, we propose to extend the rotation period of Eucalyptus plantation to 10 yr. Extending the cultivation period to 10 yr significantly improved soil quality, but the available nutrients and enzyme activity of the 15 yr plantation showed a decreasing trend. Microbial community structure may be a sensitive indicator of soil quality in Eucalyptus plantations.