Abstract:

The ecological restoration of degraded grassland is a focus of grassland ecology concern. As the main type of grasslands in Ningxia, desert steppe is both native ecological barrier and important natural resources, which has great significance in guaranteeing the state ecological safety. As a fundamental measure to protect desert steppe, the effects of fencing show on not only recovery of vegetation, but also the improvements of soil physicochemical properties. In order to better restore and reconstruct the degraded ecosystem of desert steppe, We researched the changes of texture, nutrient concentration and fractal dimension of soil particles between the grazed and the enclosure desert steppe in Ningxia. The purpose of this study was to reveal the influence of enclosure on the soil particle size and fractal characteristics of the desert grassland, and to provide a theoretical basis for the restoration and rehabilitation of the desert steppe ecosystem. The results showed that the distribution of soil particle size was from 0 μm to 250 μm. The contents of clay (< 2 μm) and silt (2~50 μm) were dominant within fence, but the contents of very fine sand (50~100 μm) had the largest proportion outside fence, furthermore, the ratio of > 250 μm was almost zero in inside and outside fence. Compared with the outside fence, the clay content of inside fence increased significantly in 0~10 cm, 10~20 cm and 20~40 cm soil layers, but the very fine sand significantly decreased (P<0.05). Fencing had different effects on soil nutrients. After enclosure,the content of TN and TP in 0~10 cm soil layer increased significantly, while the content of alkali hydrolysable nitrogen and available phosphorus decreased significantly (P<0.05), and the soil nutrients in the 10~40 cm soil layer did not show a certain change. The fractal dimension of soil particle changed from 2.65 to 2.69. Fractal dimension of soil particle increased significantly in 0~10 cm and 10~20 cm soil layers(P<0.05),but had no significant difference in 20~40 cm. In a word, fencing caused the soil particles to become fine, influenced the soil nutrient to some degree, and increased the fractal dimension of soil particle. There were significant linear relationships between soil fractal dimension and soil clay content and very fine sand content, which indicated that soil fractal dimension would become an index to measure soil texture and soil restoration.

Key words: Agropyron mongolicum community, Desert steppe, Fencing, Fractal dimension, Soil physicochemical property

摘要：

退化草地的恢复问题已经成为草地生态学关注的热点之一。作为宁夏草原的主体类型的荒漠草原，既是天然的生态屏障，也是重要的自然资源，对保障国家的生态安全具有重要意义。封育是保护荒漠草原的基本措施，封育的效果不仅表现为植被的恢复，也表现为土壤理化性质的改善。为了更好的恢复与重建荒漠草原退化生态系统，本文通过研究宁夏荒漠草原沙芦草群落围封内外土壤机械组成、土壤养分含量和土壤颗粒分形维数的变化，旨在揭示围封对荒漠草原土壤粒径组成及分形特征的影响，为荒漠草原生态系统的恢复治理与重建提供理论依据参考。研究结果发现：研究区土壤粒径分布在0~250 μm之间。其中，围栏内黏粒（< 2 μm）、粉粒（2~50 μm）含量占主导地位，围栏外以极细砂粒（50~100 μm）所占比例最大，围栏内和围栏外粒径> 250 μm的比例几乎为0。与围栏外相比，围栏内0~10 cm、10~20 cm、20~40 cm土层的土壤黏粒含量显著增加，而极细砂粒含量显著减少（P<0.05）。围封对土壤养分有不同程度的影响。围栏封育后，0~10 cm土层土壤全N、全P含量显著增加，而碱解氮、速效磷含量显著降低（P<0.05）；10~40 cm土层的土壤养分均没有表现出一定的变化规律。沙芦草群落的土壤粒径分形维数在2.65~2.69之间变动。围栏封育后，0~10 cm、10~20 cm土层的土壤粒径分形维数显著增加（P<0.05），20~40 cm土层无显著差异。总之，围封可以促使土壤颗粒细化，对土壤养分有不同程度的影响，并有助于提高土壤颗粒的分形维数；土壤粒径分形维数与土壤黏粒、极细砂粒含量均呈极显著的线性关系，说明土壤分形维数能够作为一个用来表征土壤质地以及退化土壤恢复程度的指标。

关键词: 沙芦草群落, 荒漠草原, 封育, 分形维数, 土壤理化性质