Role of nosZ I-carrying microorganisms in regulating nitrous oxide reduction during forest conversion: a comparison of plantations and a secondary forest in subtropical soils

The conversion of natural forests in subtropical regions to plantations or secondary forests has resulted in alterations in soil variables, microbial communities, and microbially mediated processes, including nitrous oxide (N₂O) emissions. However, how forest conversion influences soil N₂O reduction and the abundance and community structure of N₂O-reducing microorganisms remains unclear. Here, we investigated the impact of converting natural forests to a secondary forest and Cunninghamia lanceolata and Pinus massoniana plantations on the abundance and community structure of N₂O-reducing microorganisms in both bulk soils and soil aggregates. Compared with the secondary forest, plantations had higher soil pH and available phosphorus and moisture contents, lower soil NH₄⁺ content, but similar aggregate sizes. Compared with the secondary forest, the conversion of natural forest to plantations resulted in significantly higher soil N₂O reduction rate and increased abundances of nosZ I and nosZ II genes in bulk soils and soil aggregates. The abundance of nosZ I was higher than that of nosZ II in all tested soils and had a stronger association with N₂O reduction rate, suggesting the greater role of nosZ I-carrying microorganisms in N₂O consumption. Forest conversion had a greater impact on the community composition of nosZ I than nosZ II, mainly by increasing the relative abundances of alpha- and beta-Proteobacteria, while decreasing gamma-Proteobacteria. However, nosZ II-carrying microorganisms were exclusively dominated by Gemmatimonadetes and less affected by forest conversion. Taken together, our findings significantly contribute to our understanding of the eco-physiological characteristics of N₂O-reducing microorganisms and highlight the importance of nosZ I-carrying microorganisms in N₂O consumption in subtropical forest soils.