SOC sequestration, N and P retention in mineral soils depend on arbuscular mycorrhizal tree dominance and soil microbial traits

Most tree species are associated with arbuscular mycorrhizal (AM) or ectomycorrhizal (ECM) fungi, which play a significant role in soil nutrient cycling. This research explored the effect of AM tree dominance (high, middle, low) on soil organic carbon (SOC) sequestration, nitrogen (N), and phosphorus (P) retention in high-latitude temperate forests. The parameters related to SOC, N, and P, and soil microbial traits by the metagenome analysis were determined. The results found that compared with low-AM plots, the content of SOC was 1.6 times greater in high-AM plots, accompanied by a significant increase in fungal C and respiratory activity. Moreover, high-AM plots had higher total soil nitrogen (TN), alkali-hydrolyzable nitrogen (AN), nitrate-N, microbial biomass nitrogen (MBN), and nitrification rates compared to low-AM plots. Total phosphorus (TP) levels increased about two times, while sharp decreases in organic P and plant-available P were observed in high-AM plots compared to low-AM plots. The abundance of C, N, and P functional genes in high-AM plots increased by up to 3.6, 1.5, and 1.2 times, respectively, compared to low-AM plots. PLS-PM analysis indicated that AM tree dominance, as well as the relative abundance of functional genes (Pentaheme cytochrome c nitrite reductase - nrfA, ferredoxin-dependent nitrate reductase - narB) and dominant phyla (Thaumarchaeota, Planctomycetes, and Gemmatimonadetes), were the main predictors of the variations in SOC sequestration, and N and P retention. Our finding highlighted that soil management strategies aimed at maximizing soil C sequestration and long-term nutrient availability should consider the tree mycorrhizal dominance in high-latitude temperate forests.