Above- and belowground composition and diversity of subtropical plantations and their relationships with soil nutrient stocks

Purpose This study aimed to understand the above- and belowground community assembly in subtropical plantations, and to detect the relationship with understory plant communities, soil microbial communities and stocks of soil organic carbon, nitrogen and phosphorus. Methods We compared the composition and diversity of understory plants and microbial communities among exotic monocultures versus native conifer and broadleaved mixtures, and tested the co-structure between understory plant communities, soil microbial communities and soil characteristics. Results The two native mixtures compared to exotic monocultures had greater understory plant cover (except for the herbaceous cover that was lower) and diversity, but lower community weighted mean of shrub and herbaceous leaf carbon content. Exotic monocultures and native broadleaved mixtures had a higher biomass of each microbial group than native conifer mixtures based on phospholipid fatty acids (PLFAs) extractions. Based on high throughput sequencing, we found higher bacterial and fungal richness in native mixtures than in exotic monocultures, but lower bacterial Shannon diversity. In terms of soil nutrients, only the soil phosphorus stocks were significantly higher in native mixtures than in exotic monocultures. Moreover, in the two native mixtures there was a strong co-structure between understory plants, soil microbes and soil nutrients. Yet, fungal phyla did not have any co-structure with other taxa. Conclusion Our study highlights the important yet inconsistent roles of different plantation types in affecting the patterns of above- and belowground diversity, soil nutrients, and the maintenance of their relationships. Long-term monitoring is suggested to determine whether the main findings change with plantation restoration over time.