Effects of Successive Planting of Eucalyptus Plantations on Tree Growth and Soil Quality

The ultra-short-cycle successive planting of Eucalyptus plantations has caused environmental and social problems, and changing the rotation cycle is a very good option to solve this issue. However, the effects of successive planting on Eucalyptus growth and soil quality after changing the cultivation period are unclear. This study evaluated the effects of successive Eucalyptus planting on growth, soil nutrients, and bacterial and fungal community structure with an eight-year cultivation period. Eucalyptus plantations with different succession generations (first, second and third generation) were selected, and tree height and diameter at breast height were measured. Ten indicators of soil nutrients in different soil layers (0-20 cm and 20-40 cm) were measured, and soil bacteria and fungi were sequenced in high throughput. Results show that there is an upward trend in tree growth after three successive generations, reaching the highest timber yield in the third-generation plantation. Soil nutrients also showed changes, in the 0-20 cm soil layer, with decreased TN, NH4+-N, NO3--N and AK and increased AP, particularly for OM and TP content. In the 20-40 cm soil layer, the content of NH4+-N and NO3--N increased slightly and the soil's OM, TP, and TK content increased significantly. The diversity of bacterial and fungal communities in different soil layers increased significantly, and the community structure composition changed. Bacterial and fungal community structures were mainly driven by pH, NH4+-N, TP and AP factors and by OM, NH4+-N, TP and TK factors, respectively. Thus, successive plantings of Eucalyptus plantations with a cultivation period of eight years is conducive to the growth of trees. Some nutrients of the soil were returned, and the soil microbial diversity increased. Successive planting has brought efficiency and economic benefits while maintaining the soil's fertility.