Mechanistic insights into the bacterial regulation of soil carbon transformation in saline-alkali cotton fields under organic fertilizer application

Organic fertilizers can influence soil carbon pools by inducing structural reorganization of soil bacterial communities and expression of functional. Exploring the mechanisms underlying the effects of different organic fertilizers on soil microbial-mediated carbon cycling in saline-alkali stress environments is critical for agricultural sustainability. We conducted experiments in saline-alkali cotton fields in Xinjiang, China, to evaluate the effects of chemical fertilizer (CG), amino acid fertilizer (A), fulvic acid fertilizer (B), and humic acid fertilizer (C) on soil bacterial communities. Our results confirmed that fertilization strategy and growth period promoted microbial community ecological niche differentiation and altered structure of enriched soil bacterial communities by affecting the rhizosphere environment. Soil carbon components (SOC and MBC), inorganic nitrogen (NH4-N and NO3-N), and electrical conductivity (EC) significantly affected soil bacterial communities under fertilization treatment, whereas soil temperature and pH became increasingly influential as growth progressed. NH4-N ( r = 0.30, p < 0.01), EC ( r = 0.41, p < 0.01), and TN ( r = 0.40, p < 0.05) were the main factors affecting changes of soil bacterial genera in A, B, and C treatments, respectively. Organic fertilizers inhibited potentially pathogenic bacteria (-7.87% in C), elevated parthenogenetic anaerobic and stress-tolerant bacteria (+6.71% and +18.75% in C); they up-regulated carbon-sequestering bacteria, with species differences resulting in bidirectional effects of promoting and inhibiting carbon-degrading bacteria. Patterns of variation in the phenotypic and functional traits of soil bacteria were antagonistic synergism among organic fertilizer treatments, facultatively_anaerobic phenotypes were negatively correlated with carbon-degrading bacterial fermentation function in B treatment ( r = -0.57, p < 0.05), contrasting with a positive correlation in C treatment ( r = 0.53, p < 0.05). Our findings shed new light on how organic fertilizer induces the reconstruction of soil bacterial community structure based on rhizosphere environment and its synergistic changes in phenotypic-functional to regulate soil carbon cycling. • Fertilization strategy and growth period regulate bacterial community structure via rhizosphere environment. • Organic fertilizers inhibit potentially pathogenic bacteria, increase parthenogenetic anaerobic & stress tolerant bacteria. • Species differences of organic fertilizers result in bidirectional promotion and inhibition of carbon-degrading bacteria. • Variations of soil bacterial phenotypic & functional traits show antagonistic synergism in organic fertilizer treatments.