Variations in litter-soil properties between planted and naturally restored forests drive microbial community structure and function

How forest restoration can affect soil microbial composition and functionality remains unclear, limiting our ability to evaluate restoration approaches. Here, we used metagenomes, 16S rRNA, and ITS gene sequencing to distinguish the composition and functional attributes of soil microbial communities between plantation forest of Pinus massoniana (PF) and naturally restored secondary forest (SF) in their organic horizon and mineral soil from a typical karst region in Southwest China. Our results showed that fungal communities differed more than bacterial communities between PF and SF, while the differences in archaeal communities were not significant. The most abundant fungal phylum in both mineral soil and organic horizon was Ascomycota at SF and Basidiomycota at PF, respectively. The PF soil had lower nitrogen (N) cycling gene abundance and lower inorganic N availability compared to SF soil probably because of the poor soil and lower litter quality. The SF soil had higher abundances of genes associated with labile carbon (C) (i.e., starch, hemicellulose, cellulose, pectin, and chitin) degradation compared with PF soil, but lower abundances of genes responsible for recalcitrant C (i.e., lignin and aromatics) degradation, which was strongly correlated with the litter properties. Simultaneous effects of soil and litter variables explained >50 % of the variation in microbial community structure and functional gene composition; soil nitrate-N had the strongest effect on the soil bacterial and fungal community structure. Our results highlight the superiority of naturally restored secondary forests for improving both soil fertility and soil microbial-mediated C and N cycling functions, which can support forest managers in selecting forest restoration approaches that optimize C and N storage in forest stands.