椴树-红松林林隙大小与枯叶分解对土壤香草酸含量的影响

【目的】阔叶红松林是中国东北东部山区的地带性森林植被,林隙是广泛存在于天然红松林里的特殊微结构,探究林隙大小、枯叶分解时间和枯叶种类对林地土壤中香草酸含量的影响,为阔叶红松混交林林隙调节和红松人工林可持续经营提供依据。【方法】在黑龙江凉水国家级自然保护区椴树-红松林内,选取由掘根倒木形成的大、中、小林隙,以郁闭林分为对照,分别在林隙中心及对照土壤中埋置3种枯叶(椴树、红松、枫桦)分解袋后,分5次(61、123、147、458、519 d时)取回枯叶分解袋下0~10 cm土层土样,去除杂质并过筛后用于室内分析。采用高效液相色谱法(HPLC)测定土壤中香草酸含量。分析条件为柱温25 ℃,流速0.1 mL/min,自动进样,进样体积10 μL,检测波长280 nm。流动相A为色谱纯甲醇,流动相B为1%磷酸溶液,体积比及梯度洗脱方式为:0 min,V_A:V_B=30:70;15 min,V_A:V_B=50:50;20 min,V_A:V_B=55:45;30 min,V_A:V_B=60:40。通过方差分析,比较各林隙大小、枯叶分解时间以及枯叶种类对分解后土壤中香草酸含量的影响。【结果】林隙大小、枯叶分解时间及枯叶种类对土壤香草酸含量差异影响显著。林隙大小对土壤香草酸含量的影响不同,椴树枯叶分解后,小林隙、中林隙土壤香草酸含量普遍高于大林隙;红松枯叶分解后,小林隙土壤香草酸含量基本高于中林隙、大林隙;枫桦枯叶分解后,中林隙土壤香草酸含量高于大林隙、小林隙。多因素方差分析表明,林隙大小、枯叶种类、枯叶分解时间的交互作用对土壤香草酸含量影响显著。Post Hoc检验结果表明在椴树-红松林小林隙内,枯叶分解519 d时,枯叶种类对土壤内香草酸含量影响不明显,在椴树-红松林大林隙对照中,枯叶分解123 d时,枯叶种类对土壤中香草酸含量的影响弱于其他水平交互作用。【结论】为更好地维护椴树-红松林更新,应考虑林隙大小、枯叶种类及枯叶分解时间对土壤中香草酸含量的影响。枯叶种类在某些分解时间和某些林隙中对土壤中香草酸含量影响不明显。因此,在分析香草酸含量变化时,需要考虑各影响因素各水平的交互作用。

Effects of gap size and litter decomposition on soil vanillic acid content in Tilia amurensis-Pinus koraiensis forest

【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.