The succession patterns and drivers of soil bacterial and fungal communities with stand development in Chinese fir plantations
Authors: Zhang Yun , Chen Yuepeng , An Bo , Ma Xiangqing , Zhang Hui , Liu Qianguang , Mao Rong 
Published: December 2022

Background
The forest stand structure, microclimate, litter inputs, and soil conditions are directly or indirectly modified by forest development, which in turn influences soil organism dynamics. The effects of stand age on soil microbial composition and diversity have been extensively examined in Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) plantations, which widely distribute in southern China. However, the relative importance of contributions of vegetation succession, litter inputs, and edaphic conditions during stand development to the variations in soil bacterial and fungal communities remain largely unknown.
Methods
Bacterial and fungal communities in Chinese fir plantations were determined at two bulk soil depths over four developmental stages (young, middle-aged, mature and overmature) using 16S and ITS rRNA gene sequencing. Living plant attributes, litter variables, and soil physicochemical variables were also investigated to determine major and direct drivers of bacterial and fungal communities.
Results
The bacterial biomass and diversity were depleted, while the fungal abundance and diversity remained constant over stand age. At the taxonomic level, subordinate fungal and bacterial taxa abundances showed more significant responses to stand developmental stages than the dominant taxa. Relative depletions in bacterial oligotrophic phyla were strongly associated with improvements in soil N and P availability with stand development. Ectomycorrhizal (ECM) fungi were more abundant at the earlier stages, which coincided with substantial dynamism in the understory vegetation resulting from thinning, whereas the saprotrophic taxa abundance increased in older stands. The nonmetric multidimensional scaling (NMDS) analysis showed that the compositions of both bacterial and fungal communities were clearly divided into two groups: early-phase for young and middle-aged stands and late-phase for mature and overmature stands. Synergistic soil–plant effects primarily explained 48.3% of bacterial variation, and soil factors alone had stronger contributions (16.1%) to the structure of bacterial communities than plant attributes (4.2%) based on the variance partitioning analysis. Plants represented key factors (16.1%) contributing to variations in fungal community. The association of litter attributes with the fungal community was stronger than that with the bacterial community, but the significance was incidental.
Conclusions
The succession of bacterial and fungal community from middle-aged stage to mature stage mainly resulted from changes in forest structure and understory vegetation induced by commercial thinning and stand development of Chinese fir plantation. Vegetation succession and forest structure indirectly influenced the bacterial community by modifying the edaphic conditions. Change in vegetation during stand development structured the fungal community composition through direct (vegetation changes) and indirect pathways (organic residue inputs).