Abstract:

【Objective】We aimed to reveal the effects of the earthworm inoculation and litterfall addition on the soil enzyme activities of poplar plantations to provide a scientific basis for accurately evaluating the role of earthworms and litterfalls on the soil nutrient cycling in a poplar plantation ecosystem and optimizing the management of poplar plantations to promote their long-term productivity, maintenance and ecological service functional improvement. 【Method】A poplar plantation was chosen as the study site in Dongtai Forest Farm of Yancheng City, Jiangsu Province. We used a randomized block design with five different experimental treatments as well as a control (CK). Specifically, the treatments were poplar leaf litter mulch on the soil (T1), the poplar leaf litter incorporation into the soil (T2), earthworm inoculation (T3), poplar leaf litter mulch on the soil with earthworm inoculation (T4) and poplar leaf litter incorporation into the soil with earthworm inoculation (T5). The enzyme activities of invertase, urease, catalase and cellulase in different treatments were determined. Additionally, changes in soil microbial biomass carbon, soil microbial biomass nitrogen content, soil bulk density, soil pH value, soil total organic carbon, soil total nitrogen content and other important soil environmental factors were also analyzed. 【Result】①Compared with CK, treatments T3, T4 and T5 signi-ficantly increased the soil invertase activity and the soil urease activity, and the average increases in the soil invertase activity were 30.85%, 34.58% and 50.90%, respectively; the average increases in soil urease activity were 27.57%, 33.67% and 66.64%, respectively. ②Compared with CK, all five treatments significantly increased soil cellulase activities, with an average increase of 38.39% in T1, 51.79% in T2, 79.91% in T3, 129.33% in T4, and 149.52% in T5. ③Compared with CK, T1 and T2 treatments significantly reduced the soil catalase activity, with average decreases of 13.23% and 17.56%, respectively. T3, T4 and T5 treatments showed no significant difference compared with CK. ④The seasonal dynamic analysis showed that the soil sucrase activity was the highest in September and the lowest in March, with a minimum value of 0.40 mg/(g·d) and a maximum value of 0.77 mg/(g·d). The soil urease activity was higher in summer and autumn, and lower in spring and winter, with a minimum value of 5.61 mg/(g·d) and a maximum value of 10.57 mg/(g·d). The soil catalase activity was highest in June and lower in other seasons, with a minimum value of 2.22 mg/(g·h) and a maximum value of 4.20 mg/(g·h). The activity of cellulase was higher in summer and autumn and lower in spring and winter, with a minimum value of 2.36 mg/(g·d) and a maximum value of 6.93 mg/(g·d). Compared with CK, the earthworm inoculation and litterfall addition treatments did not change the seasonal variation patterns of the four soil enzymes. ⑤The repeated ANOVA measures showed that seasonal changes and treatments significantly affected soil invertase, urease, cellulase and catalase activities, which only had significant interactions on the soil catalase activity, but no significant interaction on soil invertase, urease and cellulase activities. ⑥The correlation analysis showed that soil invertase, urease and cellulase activities were negatively correlated with the soil bulk density and pH value, and positively correlated with soil total nitrogen, soil total organic carbon, soil microbial biomass carbon, soil microbial biomass nitrogen content and soil microbial biomass C/N ratio. The soil catalase activity was not significantly correlated with the above soil environmental factors. 【Conclusion】Soil enzyme activities of invertase, urease and cellulase in a poplar plantation could be significantly improved by the earthworm inoculation, and the effects of earthworm inoculation on soil enzyme activities of invertase, urease and cellulase could be further promoted by the poplar leaf litter incorporation into the soil than by mulch on the soil. The poplar leaf litter incorporation into the soil and earthworm inoculation treatments both significantly improved the soil enzymes indexes, while the litter incorporation into the soil with earthworm inoculation treatments further significantly improved the soil enzymes indexes. Therefore, the combination management measures of the litter incorporation into the soil and earthworm inoculation are recommended in agricultural and forestry production.

Key words: poplar plantation, earthworm, litterfall, soil enzyme activity, soil enzyme index