Abstract: 【Objective】Responses of enzyme activities to nutrient availability could provide a theoretical basis for evaluating fertilization. However, these enzyme-based reactor systems may lose reliability when the environment conditions change(e.g., soil types, organic acid microenvironment, etc.).We aimed to understand the applicability of soil enzymes on the evaluation and maintenance of fertility of black soil.【Method】Soil enzyme activity and nutrient contents were determined, and their relationships were analyzed based on the organic micro-zone system with different types and concentrations of organic acids, and incubation durations. 【Result】The results showed that the citric acid significantly improved urease activity, but oxalic acid and acetic acid inhibited urease, invertase, catalase, and phosphatase activities, and that acetic acid had the strongest inhibitory effects on soil enzymes activities. Tartaric acid only inhibited the phosphatase activities, but not that of the other enzymes. Soil organic matter increased when citric acid was added to the soil; however, tartaric acid and acetic acid mainly contributed to increasing available phosphorus concentration. Unimodal fluctuations were observed for urease, invertase, and catalase under different concentrations of citric acid; consequently, the inverse relationships between soil enzyme activities and nutrients were found. During the incubation period, activities of four enzymes remained stable or decreased slightly after the first day of incubation, but significantly increased after the third day of incubation. When incubated for 15 days, all the soil enzyme activities detected at a high level except the invertase, which showed high fluctuations during the whole incubation period. In addition, during the whole incubation period, soil enzyme activity was negatively correlated with organic matter and available phosphorus content, but not with the content of available nitrogen. Path analysis revealed that organic matter had a direct association with invertase, but this association was mediated by available phosphorus, which had direct negative effects on urease and phosphatase activities. 【Conclusion】Our results indicate that the relationships between soil enzymes activities and nutrients will change under different types, concentration, decomposing rates of organic acid. Therefore, the enzyme-based evaluation system for soil quality may lose reliability. In order to excavate the applicability of soil enzymes in soil assessment, more studies should be conducted on the relationships between soil enzymes and nutrients under different environmental conditions.