The Effect of the Conversion from Natural Broadleaved Forests into Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) Plantations on Soil Microbial Communities and Nitrogen Functional Genes

The conversion of forests could change soil characteristics and, in turn, impact the microbial community. However, the long-term effect of forest transformation on bacterial and archaeal composition and diversity, especially on nitrogen functional communities, is poorly understood. This study aimed to explore the response of soil bacterial and archaeal communities, as well as nitrogen functional groups, to the conversion from natural broadleaved forests to Chinese fir (Cunninghamia lanceolate (Lamb.) Hook.) plantations in subtropical China by 16S rRNA amplicon sequencing. Except for soil bulk density (BD) and ammonium nitrogen (NH4+-N) content, other soil properties all decreased with the conversion from natural forests to plantations. Alpha diversity of bacteria and archaea declined with the transformation from natural forests to plantations. The composition of bacteria and archaea was significantly different between natural forests and plantations, which could be mainly attributed to the change in the content of soil organic carbon (SOC), total nitrogen (TN), nitrate nitrogen (NO3--N), and available phosphorus (AP). The conversion of natural forests to plantations decreased the gene copies of ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and nifH (nitrogen fixation function) but increased denitrification gene copies (i.e., nirS, nirK, and nosZ). In summary, our study emphasizes the long-term negative effect of the conversion from natural broadleaved forests into Chinese fir plantations on the diversity and richness of soil microbial communities, thereby deeply impacting the cycling of soil nitrogen.