Prolonging Rotation of Chinese Fir to over 25 Years Could Maintain a Better Soil Status in Subtropical China

Although Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) is an important species for wood production in subtropical China, it serious declines in soil nutrients and timber productivity in plantations have been reported, probably caused by successive rotation and inappropriate cutting time. Although the significant effect of stand age on soil properties has been widely recognized, research on soil enzymes and microbial communities is relatively rare. In this study, assuming that short rotation period is one important reason for soil degradation, we measured soil physicochemical properties, microbial community composition, and enzyme activity in 3-, 15-, 25- and 45-year Chinese fir forests in Jiangxi province of China. Soil organic carbon (SOC) content decreased from 3-year to 25-year stands and then increased in 45-year stands. Despite the significant relationship between SOC and the abundance of total phospholipid fatty acids (PLFAs), no notable changes in the abundance of PLFAs were detected with increasing tree ages, except for the abundances of arbuscular mycorrhizal fungi (AMF) which were significantly higher in 25-year stands. However, the ratios of gram-positive to gram-negative bacteria (G+/G−) and fungi to bacteria (F/B) both decreased with increasing stand age. 45-year stands showed the highest activities of both phosphatase and β-glucosidase. Total potassium (TK) content and net N mineralization rate both had significant links with soil microbial community structure. Collectively, our study emphasized that stand age could significantly affect soil physicochemical properties and the microbial community. In general, 25-year stands showed poorer soil status compared to that of 45-year stands. Thus, the cutting age of Chinese fir should be increased to over 25 years to maintain a better soil status.