Effects of forest age and seasonal changes on soil microbial community diversity in Chinese fir plantations

Abstract Understanding changes in the distribution patterns and diversity of soil microbial communities from the perspectives of age-related changes, seasonal variations, and the interaction between the two factors can facilitate the management of plantations. In Chinese fir plantations, we collected soils from different depths in overmature forests (OMF), mature forests (MAF), near-mature forests (NMF), middle-aged forests (MIF), and young forests (YOF) in summer, autumn, and winter in China's subtropical regions. As the forests developed, the fungal community recovered high diversity in MAF and OMF while bacterial indicators continued to decline. Bacterial communities were more diverse in summer and fungal communities were more diverse in winter. Differences between seasons were mainly reflected in average and maximum temperature indicators. Bacteria clustered by season, while fungi clustered by developmental stage, showed differences in distribution and structure at different taxonomic levels. The fungal community is a more important indicator of soil fertility maintenance, increasing with the increase of forest age, which suggested that extending tree cultivation time could improve the soil fertility of plantations. In different seasons and different ages, we found some species worthy of attention, including Actinobacteria with high abundance in summer and Bacteroidetes in autumn in overmature forests, and Firmicutes in summer in young forests. In autumn, species like Arcopilus and Tolypocladium in near-mature and over-mature forests also have the significance of further research, which may be key species for soil fertility restoration.