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 the 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. The ¹³C/¹²C-labeled maize straw were crushed and mixed with fresh soil at ratio of 500 mg: 100 g (dry weight), respectively, then incubated in wide-neck bottles for 60 days at 25℃ in dark. Soil samples were collected destructively on the 7th, 30th and 60th days, respectively. Fluorescence enzyme detection, DNA-stable isotope probing (DNA-SIP) and high-throughput sequencing methods were used to study the content of soil dissolved organic carbon and nitrogen and extracellular enzyme activity, the diversity of straw-decomposing bacterial and fungal communities, and the differences of key species under ¹³C/¹²C-labeled maize straw addition.

Results Straw addition rapidly increased the soil dissolved organic carbon content, which significantly decreased with incubation time, while the soil dissolved nitrogen content significantly increased. Compared with lime concretion black soil, the activities of α-glucosidase (AG) and leucine-aminopeptidase (LAP) in cinnamon soil were significantly higher with straw addition, the activities of β-glucosidase (BG) and β-cellobiosidase (CBH) in both soils were significantly higher on the Day 7, and the activities of AG, β-N-acetyl-glucosaminidase (NAG) and LAP showed a pattern of first increasing and then decreasing. The composition and structure of straw-decomposing microorganisms were primarily affected by soil type, followed by decomposition time. The α-diversity of straw-decomposing bacteria was higher in cinnamon soil, while the richness of straw-decomposing fungi was higher in lime concretion black soil. The dominant species involved in straw decomposition in cinnamon soil, were Proteobacteria, Actinobacteria, Bacteroidota and Sordariomycetes, while in lime concretion black soil were 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, the promotion of the 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.