Manure-residue co-application drives SOC sequestration through differential microbial strategist selection

Abstract

This study investigated how fertilizer affects microbial communities and carbon storage in soils with contrasting organic carbon levels (16.3 % vs. 1 % SOC). Soils were incubated for 67 days (25°C, 60 % water-filled pores) under four treatments: (NH₄)₂SO₄, manure, (NH₄)₂SO₄ with garlic stalk (RGS), and manure with RGS. The results reveal that alone (NH₄)₂SO₄ increased Proteobacteria relative abundance by 129 % (significantly higher than alone manure's 51 %) in high SOC soil (16.3 %). Manure combined with RGS enhanced K-strategists (+33 %), reduced r/K ratio, stabilized carbon pools, and achieved the highest SOC increment (+21 mg g⁻¹). In low SOC soil (1 %), RGS amended treatments triggered explosive growth of Firmicutes (+382–615 %), amplified r-strategists (+13 %) with elevated r/K ratios (39−47), driving soil organic carbon accumulation (+25 mg g⁻¹). The findings demonstrate that coordinated manure application with residues optimizes soil carbon through divergent microbial strategies - reinforcing K-strategists for carbon stabilization in high-SOC soils while activating r-strategists for carbon formation in low-SOC soils, achieving soil carbon pool enhancement.