Microbial dynamics and agroforestry impact on soil ecosystem multifunctionality following forest conversion to macadamia-based systems

Forest conversion to agroforestry systems has the potential to impact soil ecosystem functions in terrestrial ecosystems and optimize crop management, which may play a critical role in sustaining soil ecosystem multifunctionality (EMF, defined as simultaneously provision of multiple ecosystem functions) in a subtropical agroforestry system. However, the impact of sowing crops on soil EMF and its relationship with soil microbe remain poorly understood within macadamia-based agroforestry systems. Here, we investigated 50 plots, including macadamia monocultures and macadamia-based agroforestry systems intercropping with dasheen, konjac, and maize, as well as adjacent primary forest in the southwest of Yunnan Province, China. Our main objective was to assess the effects of soil microbial community structure and abiotic and biotic factors on soil EMF following forest conversion. We found that forest conversion significantly decreased soil EMF and multiple individual functions. Interestingly, the macadamia intercropping dasheen system exhibited advantages in maintaining soil EMF resilience. Soil EMF was negatively correlated with increasing soil bacterial diversity, soil bulk density, and soil pH, while positively correlated with increasing soil bacterial network complexity and woody aboveground biomass. Further analyses indicated that soil bacterial network complexity was a primary contributor to soil EMF, mediating the effect of woody aboveground biomass on soil EMF. Acidobacteriota and Basidiomycota were identified as important predictors of declines in soil EMF and most individual ecosystem functions. In contrast, others like Gemmatimonadota, Firmicutes, and Chytridiomycota were associated with increases in soil EMF and most individual ecosystem functions. Furthermore, macadamia-based agroforestry systems were found to result in lower soil bacterial network complexity and woody aboveground biomass, and higher soil bulk density, leading to reduced soil EMF. These findings highlight the potential diminishment of soil EMF associated with the development of macadamia-based agroforestry systems but also suggest the effective management of microbial taxa could enhance soil bacterial network complexity, ultimately promoting resilience in soil EMF.