Induced and Natural Moss Soil Crusts Accelerate the C, N, and P Cycles of Pb-Zn Tailings

Abstract

Nutrient deficiency is the primary obstacle in tailing ecological restoration. Biological soil crusts (BSCs) are known for their C and N fixation capabilities and play a crucial role in soil P cycling. Induced BSCs through moss fragment inoculation provide a potential ecological restoration approach for tailings. In 2022, we carried out an on-site restoration of a Pb-Zn tailing pond in Yunnan Province, China. The induced moss crusts (IMCs) were monitored continuously and compared with natural moss crusts (NMCs). The chlorophyll-a content and abundance of soil microorganisms increased over time, reaching a peak at 135 days and surpassing that of NMCs. Moss crusts increased the content of C, N, and P nutrients as well as enzyme activities in the 0.5-cm surface soil. Moss crusts significantly enhanced the content of humic and protein-like/polyphenol substances, thereby raising the humic index of soil dissolved organic matter (especially NMCs). Moss crusts also raised the abundance of nitration (AOB and Nsr), denitrification (narG, napA, qnorB, and nosZ), and P-cycle (gcd, appA, phoC, phoA, and phoD) related genes, especially IMCs after 135-day inoculation. NMCs exhibited higher moss abundance in eukaryotic photoautotrophs, resulting in further enhancement of humification, which might be the reason for the decrease in fungal evenness. The increase in photosynthetic bacteria (e.g., Leptolyngbya and Nostocales) reduced the dominance of chemoautotrophic bacteria, especially the dark sulfide oxidation bacteria (Betaproteobacteriales). This trend was more pronounced in NMCs. Overall, IMCs can remarkably recover the functions of NMCs, and in some cases (e.g., abundance and diversity of key communities, soil nutrient and N & P related genes), even surpass them. Our research provides new insights into the ecological restoration and BSC succession of tailings.

Keywords: Biological soil crusts, Situ tailing restoration, Dissolved organic matter, N & P related genes, Microbial community.