Mixed Plantations Improve Soil Bacterial Similarity by Reducing Heterogeneous Environmental Selection

Abstract

Monocultures and mixed plantations have long been applied in forestry and landscape restoration to maximize the benefits of plantations. These different plantations can have unpredictable effects on the forest ecosystem. Monocultures and mixed plantations may influence soil bacterial communities, yet the underlying mechanisms of the soil bacterial community similarity response to monocultures and mixed plantations are still unknown. This study aimed to unravel how the community assembly processes and their associated factors mediate soil bacterial community similarity among monocultures and mixed plantations. We present a conceptual model to understand the mechanisms controlling soil bacterial community similarity among monocultures and mixed plantations. We tested these conceptual model hypotheses and the underlying mechanisms by conducting experiments in three plantation forest regions in southern China. We found that different monocultures led to a highly dissimilar environment, which increased heterogeneous selection and resulted in a high dissimilarity of soil bacterial communities among monocultures. Compared with monocultures, mixed plantations afford more similar environmental conditions for soil bacterial communities and decrease the heterogeneous selection process, leading to a higher soil bacterial similarity among mixed plantations. In addition, we demonstrate that stochastic processes are also the dominant driver in determining the soil bacterial community similarity among mixed plantations. Overall, the conversion from monocultures to mixed plantations affects the community assembly process by altering environmental similarity and edaphic factors, subsequently determining the similarity of soil bacterial communities. Our study can provide scientific guidance for exploring the role of mixed plantations in forest management.