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Aims: Organic fertilizer addition plays a significant role for soil organic carbon (SOC) storage. The interaction between bacteria and clay minerals for the mechanism of SOC storage with organic fertilization was investigated in saline-alkaline paddy soil. Methods: A 9-year field experiment was arranged, which included: (a) CK, without fertilizer addition, (b) NPK, mineral N, P and K fertilizer addition, (c) NPKC1, and (d) NPKC2, mineral N, P and K fertilizer plus 450 and 900 kg C ha−1, respectively. Results: In comparison to only mineral fertilization, the content of humic acid-C and humin-C was significantly increased by 58.8%–70.6% and 46.9–53.1% with organic fertilizer addition, respectively. The 2:1 type clay minerals (vermiculite and illite) were also increased, which were positively correlated with SOC storage due to the formation of clay minerals-humus complexes. Meanwhile, the abundance of Geobacter and Anaeromyxobacter was increased with organic fertilization, which accelerated the transformation of clay minerals by promoting Fe reduction, and then increased SOC storage. While, compared with NPKC1 treatment, more Gammaproteobacteria and Anaerolineae, involved in the decomposition of SOC, were found in NPKC2 treatment. Relative to NPK treatment, SOC storage of NPKC1 and NPKC2 treatments increased by 23.3% and 29.8%, respectively, and there was no significant difference between the two treatments. Conclusions: Therefore, appropriate addition of organic fertilizer is a better fertilization practice to promote stability and storage of SOC, which provided an important contribution to elucidate the role of mineral-microbial interactions for storage of SOC in saline-alkaline paddy soil. [ABSTRACT FROM AUTHOR]

Organic fertilizer can improve phosphorus (P) bioavailability, while the mechanism of microbial-driven clay mineral transformation on P retention and utilization with organic fertilization is still unclear. An 8-year organic fertilization experiment was carried out in saline alkaline paddy soil with five treatments: (1) CK, no fertilization; (2) NK, mineral N and K fertilization; (3) NPK, NK with mineral P fertilization; (4) NPKC1, NPK with 450 kg C ha−1 year−1; (5) NPKC2, NPK with 900 kg C ha−1 year−1. The results showed that, compared with NPK treatment, the percentage of illite with more P adsorption sites was increased by 26.8% and 20.7% in NPKC1 and NPKC2 treatments, respectively. Meanwhile, transmission electron microscopy-energy dispersive X-ray spectroscopy analysis further confirmed that there was more P adsorption on silicate clay minerals. Compared with NK treatment, the content of total P and available P was significantly increased with organic fertilization. Besides, the diversity of bacterial community was also increased by organic fertilizer addition, redundancy analysis showed that soil organic carbon was the main factor in the diversity of bacterial community. The relative abundance of Firmicutes and Gemmatimonadetes was promoted, which drove the transformation of clay minerals and improved P availability, respectively. Compared with NPK treatment, P use efficiency in NPKC1 and NPKC2 treatments was increased by 47.2% and 58.2%, respectively, while no significant difference was found between the two treatments. Therefore, appropriate organic fertilization was a better fertilization practice to improve P retention and utilization through bacteria-driven clay mineral transformation in saline-alkaline paddy soil. [Display omitted] • Organic fertilizer addition promotes clay mineral transformation from kaolinite to illite. • P retention was increased by transformation of clay mineral with organic fertilizer addition. • Soil characteristics and microorganism drive transformation of clay mineral. • The rice yield and P utilization efficiency were increased with organic fertilization. [ABSTRACT FROM AUTHOR]