黄土高原半干旱丘陵区不同树种纯林土壤性质极化研究

人工或天然纯林土壤性质呈现偏离原平衡态并朝某个方向非平衡或极端化发展的现象被作者称为极化。作者提出了抗极化域(W)、抗极化度(R)、极化度(P)和极抗比(I)等土壤极化的表征指标,并采用多样地多样点混合采土法对黄土高原半干旱丘陵区进入成熟生长期的不同树种纯林和混交林土壤性质进行了广泛测定和极化分析。结果表明:(1)不同树种林地属于极强度极化(P>0.20)的土壤性质分别为:油松纯林的化学性质,侧柏、刺槐和沙棘纯林的化学和生物学性质,白榆纯林的化学、生物学性质和微量元素,白桦纯林的生物学性质,茶条槭纯林的生物学和物理性质。(2)总体而言,油松和刺槐纯林会引起土壤的严重贫养化;侧柏纯林会引起土壤的严重富养化;白榆纯林虽然会引起土壤的富养化,但却使得微量元素越来越缺乏;白桦纯林主要会引起土壤生物学性质的恶化;茶条槭纯林土壤有偏贫养化和生物学性质恶化的趋势;沙棘纯林会导致土壤严重贫养化和生物、物理性质的恶化;小叶杨纯林土壤性质尚未发生明显极化。(3)总体而言,小叶杨、油松的抗极化能力均较强,而白榆的抗极化能力最低;相对于林木抗极化能力,土壤的绝对综合极抗比属于中等以上(Ia>0.40)的性质分别为:油松纯林的化学、物理性质,侧柏、刺槐和白榆纯林的所有性质,白桦纯林的生物学、物理和化学性质。

Soil polarization under pure stands of different tree varieties in semi-arid hilly areas of the loess plateau

As every tree species is unique in biological and ecological characteristics, the presence of mono species stands of forests, natural or planted may cause variation of soil properties away from equilibrium toward imbalance or certain extremity, which is called "soil polarization" by the author. At the same time, a number of characterization indexes, i.e. width of anti polarization (W), resistance to polarization (R), polarization (P) and ratio of polarization resistance to polarization (I = P/R) were proposed for polarization analysis based on results of determination of soil properties of soil samples collected from a variety of mature stands of pure and mixed forests using a multi-point mixed sampling method at multiple sites in the semi-arid, hilly area of loess plateau. Results show very strong polarization (P>0.20) of the following soil properties: chemical properties under Pinus tabulaeformis forest; chemical and biological properties under Platycladus orientalis, Robinia pseudoacacia and Hippophae rhamnoides forests; chemical, biological properties and trace elements content under Ulmus pumila forest; biological properties under Betula platyphylla forest; and biological and physical properties under Acer ginnala forest. Among the species in this study, pure stands of P. tabulaeformis and R.pseudoacia resulted in serious depletion of soil nutrient reserves; Pure stands of P. orientalis increased soil fertility; Pure stands of U. pumila increased soil fertility but decreased trace elements content; Pure stands of B. platyphylla worsened soil biological properties; Pure stands of A. ginnala led to depletion of soil nutrient reserves and deterioration of soil biological properties; and Pure stands of H. rhamnoides did to depletion of soil nutrient reserves and degradation of soil biological and physical properties. The anti-polarization capacities of P. simonii and P. tabulaeformis were the highest and of U. pumila the lowest. Relative to anti-polarization capacity, the ratios of polarization resistance to polarization of the stands fell into the category of more than "medium" (I_a＞0.40)including chemical and physical properties under P. tabulaeformis forest, all the soil properties as a whole under P. orientalis, R.pseudoacia and U. pumila forests, and biological, physical and chemical properties under B. platyphylla forest.