乌兰布和沙漠不同灌丛土壤颗粒多重分形特征及其与有机碳分布的关系

w（SOC）（SOC为土壤有机碳，soil organic carbon）及其分布状况显著受到土壤PSD（particle-size distribution，粒径分布）和有机质相互胶结方式的差异影响，而w（SOC）可反映土壤结构优劣程度，表征土壤肥力状况及碳库饱和度.以乌兰布和沙漠沙冬青、花棒、猫头刺、白刺和梭梭灌丛下0~100 cm深度风沙土为研究对象，通过野外分层采样与室内测试，采用多重分形理论探讨土壤特性和w（SOC）分布特征及其相互关系，反映土壤结构及肥力状况.结果表明:① 不同灌丛下的土壤均具有良好的分形特征，并且灌丛可通过降低风速，使≤ 50 μm的优质颗粒在周围表层土壤沉降，而优质颗粒数量与w（SOC）、D₀（粒径分布范围）及D₁（分布均匀程度）极显著正相关（P < 0.01），与D₁/D₀（分布离散程度）极显著负相关（P < 0.01）；② 各灌丛下w（SOC）的大小关系与D₁、D₀相似但与D₁/D₀完全相反，即w（SOC）可表征PSD状况进而反映土壤结构优劣程度，并且在沙冬青灌丛的>20~30、>60~80 cm土层出现两次峰值，分别为11.958、11.928 g/kg；③ 对D₀的扩大及D₁/D₀的降低程度以沙冬青灌丛最为明显，但对D₁的降低程度则以花棒灌丛最为明显.研究显示，多重分形理论可很好地描述乌兰布和沙漠风沙土性质，并且适生灌丛中沙冬青及花棒可更好地改善土壤颗粒及SOC特征，故可通过种植二者局部改良土壤及增加碳库饱和度. 

Soil Particle Multi-Fractals and Soil Organic Carbon Distributions and Correlations under Different Shrubs in Ulan Buh Desert

Particle-size distribution (PSD) and contents of soil organic carbon (SOC) are regarded as soil fundamental characteristics, since SOC contents and distribution conditions can reflect the virtues or degree of defects of soil structure and soil fertile status. Multi-fractal theory has been widely used to evaluate PSDs, soil quality and SOC characteristics. Contents of SOC and distributions are significantly impacted by various methods of combination between soil particles and soil organic matters of different PSD. Therefore, we dug depths of 0-100 cm (0-10, > 10-20, > 20-30, > 30-40, > 40-60, > 60-80, > 80-100 cm) aoelian sandy soil profiles under Ammopiptanthus mongolicus, Hedysarum scoparium, Oxytropis aciphylla, Nitraria tangutorum and Haloxylon ammodendron shrubs coverage separately in Ulan Buh Desert, and from those as samples measured PSDs character and SOC contents and the distribution using multi-fractal theory, in order to analyze their correlations to give expression to soil structure and fertile status. The results showed that:(1) Soil under various shrubs all well reflected multi-fractal character; shrubs could decrease wind velocity to deposit fine particles which were ≤ 50 μm and supplement plasma materials carried by wind erosion. These resulted in positive significant correlation with w(SOC) and range of PSD, homogeneous degree of PSD (P < 0.01) and negative significant correlation with dispersion degree of PSD (P < 0.01). (2) Orders of w(SOC) under different shrubs were similar with D₁ and D₀, but totally opposite to D₁/D₀; w(SOC) could reflect PSDs status to illustrate virtues or defect degree of soil. w(SOC) showed double summit values under A. mongolicus at 20-30 and 60-80 cm soil layer, which were 11.958 and 11.928 g/kg. (3) A. mongolicus could enlarge D₀ but decrease D₁/D₀ significantly, and H. scoparium could decrease D₁ significantly, so H. scoparium and A. mongolicus could promote PSD status more significantly to raise w(SOC). The results showed that multi-fractal theory can describe aeolian sandy soil property in Ulan Buh Desert appropriately, and A. mongolicus and H. scoparium included in suited shrubs of local environment can improve soil particle status and promote soil quality in partial desert area and increase saturation of carbon pool.