间伐强度对华南2种近自然改造人工林土壤养分释放的影响

Influence of Thinning Intensity on Soil Nutrient Release in Two Near-nature Plantations in South China

摘要:

为评估间伐强度对土壤养分释放特征的影响，以广东省东莞市大岭山林场为研究区，选取经13~17 a近自然改造(间伐+补植乡土树种)的马占相思(Acacia mangium)和尾叶桉(Eucalyptus urophylla)人工林，对3种间伐强度下(未间伐、间伐30%和间伐60%~70%)土壤碳(C)、氮(N)、磷(P)含量及与N、P养分获取的相关胞外酶活性进行测定。结果表明，与未间伐相比，马占相思间伐样地速效N、P的含量平均提升了28%和71%，尾叶桉间伐样地平均提升了21%和33%。2种间伐样地土壤C、N和P获取酶的活性均出现不同程度的降低。通过对比2种间伐强度下生态酶化学计量比值和矢量特征，表明间伐能够有效缓解养分转化所需的C限制，但过度间伐也可能进一步导致土壤N限制。这表明中等间伐(30%)能够兼顾2种人工林土壤N、P养分的释放和植被多样性的提高，应为2种林分近自然改造中间伐强度的最优选择。

Abstract:

To assess the impact of thinning intensity on soil nutrient release characteristics, the Daling Mountain Forest Farm in Dongguan City, Guangdong Province was selected as the study area. Soil carbon (C), nitrogen (N), and phosphorus (P) contents, as well as the extracellular enzyme activities related to N and P nutrient acquisition, were measured in 13- to 17-year-old Acacia mangium and Eucalyptus urophylla plantations that had undergone near-natural transformation (thinning + planting native tree species) under three thinning intensities (no thinning, 30% thinning, and 60%–70% thinning). The results showed that compared with the unthinned plots, the available N and P contents in the thinned plots of A. mangium increased by an average of 28% and 71%, respectively, and those in the thinned plots of E. urophylla increased by an average of 21% and 33%, respectively. The activities of soil C, N, and P acquisition enzymes in both thinned plots decreased to varying degrees. By comparing the stoichiometric ratios and vector characteristics of ecological enzymes under the two thinning intensities, it was indicated that thinning could effectively alleviate the C limitation required for nutrient transformation, but excessive thinning might further lead to soil N limitation. It was suggested that moderate thinning (30%) could balance the release of N and P nutrients in the soil and the improvement of vegetation diversity in both plantations, and should be the optimal choice for thinning intensity in the near-natural transformation of these two forest types.