Reforestation practices have varied the resilience of nosZ-type denitrifier communities: A 40-year soil chronosequence study

Forested areas that have been subject to clearing are known to have increased nitrous oxide (N2O) emission. This may be due to reductions in populations of soil bacteria possessing the nosZ gene, the only recognized consumer of N2O, which encodes nitrous oxide reductase and raises several questions about the capacity of a soil to respond and recover from perturbations. We investigated temporal patterns in soil denitrification potential (DP) and the abundance, diversity and resilience of nosZ-type denitrifiers in secondary successional forests and Chinese fir (Cunninghamia lanceolate) monoculture. The increasing age of the reforestation was associated with an increased abundance and resilience of the nosZ gene and also with reduced soil DP. The measured nosZ resilience and α-diversity were higher in secondary forest soils than in Chinese fir monoculture, indicating that nosZ-type denitrifiers recovered from forest disturbance faster under natural secondary succession than in the Chinese fir monoculture. Random forest analysis identified the litter C/N ratio and litterfall production as the main predictors of the resilience index of nosZ-type denitrifiers. Significant differences in nosZ community composition were observed between the two forest types (P = 0.001), with the dominant genus Massilia and rare taxa (Stenotrophomonas and Gemmata) identified as important factors explaining variation in DP from soil. Structural equation modeling (SEM) analysis revealed that litterfall production directly or indirectly explained variation in soil DP via paths associated with the abundance and composition of nosZ-type denitrifiers. Our results highlight that natural secondary forests play an important role in restoring soil nosZ gene and mitigating soil N2O emissions.