Lignite bioorganic fertilizer enhanced microbial co-occurrence network stability and plant–microbe interactions in saline-sodic soil

Lignite-converted bioorganic fertilizer substantially improves soil physiochemical properties, but little is known about how lignite bioorganic fertilizer (LBF) affects soil microbial communities and how the changed microbial communities impact their stability, functions, and crop growth in saline-sodic soil. Therefore, a two-year field experiment was conducted in saline-sodic soils in the upper Yellow River basin, Northwest China. Three treatments, i.e., the control treatment without organic fertilizer (CK), the farmyard manure treatment (FYM) amended with 21 t ha-1 (same as local farmers) sheep manure, and the LBF treatment amended with the optimal rate of LBF (3.0 and 4.5 t ha-1), were designed in this study. The results showed that after two years of application of LBF and FYM, the percentage of aggregate destruction (PAD) was significantly reduced by 14.4 % and 9.4 %, respectively, while the saturated hydraulic conductivity (Ks) was obviously increased by 114.4 % and 99.7 %, respectively. The LBF treatment significantly increased the contributions of nestedness to total dissimilarity by 101.4 % and 156.2 % in bacterial and fungal communities, respectively. LBF contributed to the shift from stochasticity to variable selection in the assembly of the fungal community. The LBF treatment enriched the bacterial classes of Gammaproteobacteria, Gemmatimonadetes, and Methylomirabilia and fungal classes of Glomeromycetes and GS13, which were mainly driven by PAD and Ks. Additionally, the LBF treatment significantly increased the robustness and positive cohesions and decreased the vulnerability of the bacterial co-occurrence networks in both 2019 and 2020 in comparison with the CK treatment, indicating that the LBF treatment increased stability of bacterial community. The relative abundance of chemoheterotrophy and arbuscular mycorrhizae in the LBF treatment were 89.6 % and 854.4 % higher than those in the CK treatment, respectively, showing that the LBF enhanced sunflower-microbe interactions. The FYM treatment improved the functions mainly regarding sulfur respiration and hydrocarbon degradation by 309.7 % and 212.8 % in comparison with the CK treatment, respectively. The core rhizomicrobiomes in the LBF treatment showed strong positive connections with the stability of both bacterial and fungal co-occurrence networks, as well as the relative abundance and potential functions of chemoheterotrophy and arbuscular mycorrhizae. These factors were also linked to the growth of sunflowers. This study reveals that the LBF improved sunflower growth due to enhance microbial community stability and sunflower-microbe interactions through altering core rhizomicrobiomes of saline-sodic farmland.