Straw chemistry overrides microbial and environmental controls on straw decomposition in high-latitude mollisols

Straw returning represents a widely adopted strategy for soil organic carbon (SOC) sequestration in agricultural ecosystems, yet its efficacy is affected by straw chemistry and edaphic conditions. However, the mechanisms regulating straw decomposition in high-latitude mollisol regions remain elusive.

We carried out a 17-month field experiment using the litterbag method with bags buried at 15 and 30 cm depths across two sites with different accumulated temperatures (Nenjiang and Harbin) to examine maize straw decomposition dynamics and the relationships between straw mass remaining and factors such as soil environment, soil properties, soil microbial communities, and straw chemistry. Solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy was used to characterize straw chemical composition, and phospholipid fatty acid (PLFA) analysis was employed to determine microbial community composition.

Maize straw mass remaining was governed primarily by site and decomposition time, with limited influence of soil depth. During decomposition, O-alkyl C (predominantly carbohydrates) continuously decreased, while Alkyl C and Aryl C (mainly lignin derivatives) gradually became enriched. The decomposition degree at the Harbin site was higher than that at Nenjiang. Bacterial and fungal communities were primarily governed by straw nitrogen, C/N ratio, and O-alkyl C, whereas both Gram-negative (G⁺) and Gram-positive (G^-) bacteria responded to tensile strength (TS), straw nitrogen, and soil moisture (SM). Actinomycetes exhibited distinct associations with soil total nitrogen (TN), mean weight diameter (MWD), SM, TS, and straw chemistry (Carbonyl C). PLS-PM revealed that straw chemistry was strongly associated with decomposition dynamics. The soil environment, soil properties, and microorganisms jointly influence straw chemistry, thereby affecting its decomposition. These outcomes reveal the multi-factor control of straw decomposition and provide guidance for straw returning strategies in farmland ecosystems in cold regions.