High-Quality Litter and Exogenous Cellulase Enhance Soil Nutrient Cycling and Enzymatic Activities

Litter decomposition is important for soil nutrient cycling, but how the quality of litter links to nutrient dynamics is still unclear. In this work, high-quality Populus alba × P. Berolinensis, widely planted in Northeast China, and low-quality maize straw were selected as samples for a comparative study. In a short-term controlled litter decomposition incubation experiment, we applied different concentrations (25 u/g and 50 u/g) of biocatalyst (cellulase) to accelerate litter decomposition. Destructive sampling was conducted at 3, 7, 14, and 28 days to examine the influence of exogenous cellulase and litter with varying C:N ratios on the stoichiometric balance of soil carbon and nitrogen contents, as well as associated enzymatic activity. Litter addition significantly increased soil nutrients. Low nitrogen limited nutrient release during the decomposition of maize straw. After treatment, the soil organic carbon (SOC), total nitrogen (TN), microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN) in maize straw were 11.7%, 11.35%, 24.49%, and 39.7% lower than those in high-quality Populus alba × P. Berolinensis, respectively. Exogenous cellulase addition increased microbial biomass and β-D-glucosidase activity. The promotion of soil urease (S-UE), sucrase (S-SC), and β-D-glucosidase (S-β-GC) activities was more significant in combination with litter and exogenous cellulase. In addition, soil nutrients were directly affected by the litter C:N ratio and indirectly affected by cellulase. Overall, these results suggest that high-quality litter better facilitates soil nutrient cycling and accumulation due to its higher carbon and nitrogen release.