Abstract:

【Objective】Broad-leaved Pinus koraiensis forest forms zonal forests in the mountainous areas of the eastern part of Northeast China. Forest gaps are special micro-structures widely existing in natural P. koraiensis forest. This study explored the effects of gap size, litter decomposition duration and litter species on vanillic acid content in the forest soil to provide a theoretical basis for gap regeneration of broad-leaved P. koraiensis mixed forest and sustainable management of P. koraiensis plantations.【Method】Large, medium and small forest gaps formed by uprooted trees were selected in Tilia amurensis-P. koraiensis forest in Liangshui National Natural Reserve. Closed stands were set up as controls. Decomposition bags containing litter from three different tree species (T. amurensis, P. koraiensis and Betula costata) were embedded in the soil at the center of the gaps and in the controls. Samples of the soil below the decomposition bags were collected to a depth of 10 cm at five time intervals (61, 123, 147, 458 and 519 d from the day the bags were embedded). Soil impurities were removed and the samples were sieved for laboratory analysis. The soil vanillic acid content was determined by high performance liquid chromatography using the following analytical conditions: 25 ℃ column temperature, 0.1 mL/min flow rate, 10 mL automatic injection volume, and 280 nm detection wavelength. Mobile phases A and B were pure methanol and 1% phosphoric acid solution, respectively. The gradient elution method was: 0 min, V_A:V_B=30:70; 15 min, V_A:V_B=50:50; 20 min, V_A:V_B=55:45; and 30 min, V_A:V_B=60:40. The effects of gap size, litter decomposition duration and litter species on soil vanillic acid content were analyzed by using ANOVA. 【Result】Gap size, litter decomposition duration and litter species all had significant effects on the vanillic acid content of the soil. There was an interaction between gap size and litter species as follows: in small and medium gaps, vanillic acid content was generally higher than that in large gaps after decomposition of T. amurensis litter. In small gaps, it was generally higher than that in medium and large gaps after decomposition of P. koraiensis litter, and in medium gaps, it was higher than that in large and small gaps after decomposition of B. costata litter. Multivariate analysis of variance showed that the effects of gap size, litter decomposition duration and litter species had significant effects on vanillic acid content in the soil. A Post Hoc test indicated that in the small gaps of T. amurensis-P. koraiensis forest, after litter decomposition for 519 d, the effect of litter species on the soil vanillic acid content was not significant. In the large closed stand of T. amurensis-P. koraiensis forest, after litter decomposition for 123 d, the effect of litter species on the soil vanillic acid content was weaker than that of the other horizontal interactions.【Conclusion】In order to better analyze the regeneration of T. amurensis-P. koraiensis forest, the effect of gap size, litter decomposition duration and litter species on the content of vanillic acid in the soil should be comprehensively investigated. The effect of litter species on soil vanillic acid content was not significant for certain decomposition durations and gap sizes. Therefore, when analyzing the change in soil vanillic acid content, it is necessary to consider the interactions of various factors and levels.

Key words: Tilia amurensis-Pinus koraiensis forest, forest gap, litter decomposition, soil vanillic acid, Liangshui National Natural Reserve