Abundant fungal and rare bacterial taxa jointly reveal soil nutrient cycling and multifunctionality in uneven-aged mixed plantations

Abstract Uneven-aged silvicultural practices can maintain habitat continuity and enhance biodiversity. Soil microorganisms play critical roles in multiple ecosystem functions (i.e., multifunctionality). However, little is currently known regarding the role of the microbial community in driving soil nutrient cycling and multifunctionality (SMF) in uneven-aged mixed plantations. In this study, we investigated soil bacterial and fungal community compositions and diversities, single-function related carbon (C), nitrogen (N), and phosphorus (P) cycling, and SMF indices in monoculture plantation (as a control) and three uneven-aged mixed plantation stands (4, 7, and 11 years old). Our results demonstrated that the soil C, N, P cycling, and SMF indices in uneven-aged mixed plantations increased by 17.9–55.2%, 20.0–54.0%, 0.7–21.6%, and 16.3–30.1% compared to monoculture plantation. The soil fungal alpha diversity (richness and Shannon diversity), nutrient cycling, and SMF significantly improved with stand age, but bacterial alpha diversity showed less variation. The beta diversities of bacteria and fungi showed notable variation with stand age and were predominantly affected by stand age and soil properties (soil organic C, total P, and C/N ratio), respectively. Additionally, the temporal turnover within the fungal community was higher than the turnover rates of the bacterial community. Soil fungal diversity and biomass were more sensitive to the stand structure change over a short period (11 years) than bacterial diversity and biomass. Furthermore, the fungal beta diversity and fungi/bacteria (F/B) ratio were strongly and positively correlated with nutrient cycling and SMF. Most importantly, the abundant fungal taxa (e.g., Mucoromycota and Mortierellomycota) were the major drivers of SMF, followed by rare bacterial taxa (e.g., Nitrospirae and Elusimicrobia). These findings indicate soil fungal and bacterial communities have different responses and undertake important roles in maintaining nutrient cycling and SMF when a monoculture plantation is converted into an uneven-aged mixed plantation.