Objectives The key characteristics and the temporal succession of straw-decomposing microorganisms in different soil types were clarified to provide a theoretical basis for fully exploring straw-decomposing functional microorganisms and improving utilization efficiency of straw resources in different farmlands.

Methods A microcosm incubation experiment was set up using the typical cinnamon soil and lime concretion black soil in the North China Plain. Crushed ¹³C/¹²C-labeled maize straw were mixed with fresh soil at a ratio of 500 mg∶100 g (dry weight), and incubated in wide-neck bottles for 60 days at 25℃ in the dark. Soil samples were collected destructively on days 7, 30 and 60. Fluorescence enzyme assays, DNA stable isotope probing (DNA-SIP) and high-throughput sequencing were used to analyze soil dissolved organic carbon and nitrogen, extracellular enzyme activity, diversity of straw-decomposing bacterial and fungal communities, and key microbial taxa involved in straw decomposition.

Results Straw addition rapidly increased soil dissolved organic carbon content, which subsequently decreased with incubation time, while soil dissolved nitrogen content increased significantly. Compared with lime concretion black soil, activities of α-glucosidase (AG) and leucine-aminopeptidase (LAP) in cinnamon soil were significantly higher with straw addition. Activities of β-glucosidase (BG) and β-cellobiosidase (CBH) in both soils were significantly higher at Day 7, and activities of AG, β-N-acetyl-glucosaminidase (NAG) and LAP showed a pattern of increasing initially and then decreasing. Straw-decomposing microbial community composition and structure were primarily affected by soil type, followed by decomposition time. Straw-decomposing bacterial α-diversity was higher in cinnamon soil, while the richness of straw-decomposing fungi was higher in lime concretion black soil. Dominant species involved in straw decomposition in cinnamon soil included Proteobacteria, Actinobacteria, Bacteroidota and Sordariomycetes, while lime concretion black soil was domimated by Proteobacteria, Actinobacteria, Acidobacteriota, Sordariomycetes and Eurotiomycetes. As the decomposition time prolonged, the relative abundance of Thermomonas and Sphingomonas, which were relatively abundant in cinnamon soil, significantly decreased, while the relative abundance of Staphylochum significantly increased. The relative abundance of Caterulispora and Jatrophihabitans in lime concretion black soil significantly decreased, while Acidobacteria, Mizugakiibacter, Trechispora, Terracidiphilus and Conlarium significantly increased at the later stage of incubation. The correlation analysis results showed that high soil pH and low fertility significantly increased soil AG and LAP activity and promoted straw carbon and nitrogen nutrient conversion by enriching Marmoricola, Aeromicrobium, Blastococcus, Arenimonas, Staphylotrichum and Schizothiocium, while the low soil pH and high fertility promoted the growth of Chrysosporium, Terracidiphulus, Jatrophihabitans and Cladohilophora, and increased soil BG, CBH, NAG to enhance the soil microbial activity under straw addition.

Conclusions Soil properties shape the composition and structure of key straw-decomposing microorganisms with environmental preferences, thereby influencing the characteristics of soil carbon and nitrogen transformation under straw return. In cinnamon soil, which has a relatively high pH and low fertility level, the enrichment of straw-decomposing bacteria such as Marmoricola, Aeromicrobium, Arenimonas, Blastococcus, as well as straw-decomposing fungi like Staphylotrichum and Schizothecium, significantly enhances activities of AG (α-glucosidase) and LAP (leucine-aminopeptidase), thus facilitating the transformation of straw carbon and nitrogen nutrients. In contrast, in lime concretion black soil with a lower pH and higher fertility level, promotion of growth and activities of fungi such as Chrysosporium, Terracidiphilus, Jatrophihabitans, and Cladophialophora increases activities of BG (β-glucosidase), CBH (β-cellobiosidase), and NAG (β-N-acetyl-glucosaminidase), thereby accelerating the transformation of straw carbon and nitrogen nutrients.