Enrichment of keystone fungal taxa after flue gas desulphurization gypsum application drives reclamation of the saline-sodic soil

Soil salinization is a major threat to sustainable agriculture in the western part of Songnen Plain, Northeast China. Flue gas desulphurization gypsum (FGDG) is commonly used for reclaiming of saline soils due to its high efficiency and cost-effectiveness. However, the responses of soil and root-associated fungi after FGDG amendment and the keystone fungal taxa in determining soil reclamation effect remain elusive. In this study, a long-term field experiment was conducted to explore the effect of different levels of one-time FGDG application on the soil reclamation and the herbage (Leymus chinensis) growth. Our results showed that the FGDG application greatly reduced soil salinity level, increased soil fertility and fungal diversity, and promoted aboveground biomass of L. chinensis, whereas reduced FGDG dose to 60% of gypsum requirement (GR) exhibited non-significant difference on these characters compared with 100% GR treatment. We further discovered that both soil and root fungal communities were greatly changed after FGDG application, with root fungal community more sensitive than soil fungi. Through applying the Random Forest model, the arbuscular mycorrhizal fungi Glomeromycota was identified as the keystone taxa in predicting the soil salinity, soil fertility, and plant growth trait. Intriguingly, some Glomeromycota-affiliated ZOTUs were consistently enriched in the FGDG application treatments, and acted as keystone hubs in the co-occurrence network of fungal communities. Together, our study provides new insights that the enrichment of keystone Glomeromycota after FGDG application determines the reclamation of the saline-sodic soil, which would guide the microbial-based strategy for the development of degraded ecosystems.