Soil multifunctionality and nutrient cycling-related genes in Cunninghamia lanceolata plantations: metagenomic perspective insights into ecological restoration

Abstract

The widespread cultivation of Cunninghamia lanceolata in China has led to soil degradation and decline in microbial diversity, which have a significant impact on supporting forest ecological services. However, little is known about the long-term consequences from forest management practices on the bacterial functional genes associated with soil nutrient cycling. Here, metagenomic sequencing was used to investigate the soil bacterial functional genes involved in carbon (C), nitrogen (N), and phosphorus (P) cycling in a 16-year pair experiment of pure (C. lanceolata) and mixed plantations (C. lanceolata + Betula luminifera). The results showed that the mixed plantations had much higher soil nutrient content as well as enzyme activity, thereby improving soil multifunctionality (SMF). Forest management practices resulted in differences in the structural and functional composition of soil bacterial communities, such as Chloroflexi, Firmicutes and acid metabolism were enriched in pure plantations, while Acidobacteria, Planctomycetes and amino acid metabolism were enriched in mixed plantations. Compared with monocultures, mixed plantations had higher abundance of genes participated in C degradation, C fixation, methanogenesis, N cycling and P solubilization. The CNP cycling genes also varied with taxon-specific responses to forest management. Forty-seven nearly entire bacterial metagenome-assembled genomes (MAGs) were obtained, in which MAGs enriched in mixed plantations had more functional genes involved in CNP cycling. Notably, acidophilic Acidobacteria played important roles in reduction of Fe(III) and the subsequent release of organic P. In all, our results demonstrated that the use of mixed plantations enhances a number of soil functions via its influence on the abundances of keystone taxa and functional genes, providing a foundation for developing forest management strategies in subtropical regions. In future researches, attention should be paid to the effects of mixed plantations on soil microbial diversity and nutrient cycling across various seasons.