植被覆盖对科尔沁沙地土壤生物结皮及其下层土壤理化特性的影响

为了解不同植被覆盖对沙地土壤生物结皮及其下层土壤的影响，于2006年调查了科尔沁沙地冷蒿、小红柳、杨树和樟子松等植被封育区土壤生物结皮及结皮下0～5 cm土壤的理化特性.结果表明：经过15年的封育保护和植被建设，科尔沁沙地天然植被和人工植被下流动沙地大部分被生物结皮所覆盖，其结皮覆盖度可达60%～80%，厚度1～2 cm;在调查的几种植被中，小红柳植被区的土壤结皮厚度、硬度、粘粉粒、有机质和养分含量最高，其次是樟子松林地，杨树林地和冷蒿植被区相对较差;几种植被区的苔藓结皮的结皮厚度、硬度、粘粉粒、有机质和养分含量均优于地衣结皮;与流动沙地相比，结皮下0～5 cm土壤的理化特性有明显改善，改善程度苔藓结皮强于地衣结皮，小红柳和樟子松植被区强于杨树林地和冷蒿群丛;土壤结皮及结皮下表土理化特性的变化既受植被覆盖类型的影响，也受制于土壤结皮的发育.由于枝叶繁茂的中、高植被有利于降风滞尘和产生较多的凋落物，因而更能促进沙地结皮发育和土壤改良，而苔藓结皮较地衣结皮更有利于其下层土壤理化特性的改善.

Effects of vegetation cover on physical and chemical properties of bio-crust and under-layer soil in Horqin Sand Land

To understand the effects of different vegetation cover on the bio-crust and its under-layer soil in Horqin Sand Land, the bio-crust and 0-5 cm soil samples in Artemisia frigida, Salix microstachya, Populus simonii, and Pinus sylvestris var. mongolica stands were collected, and their physical and chemical properties were studied. After fifteen years enclosure protection and vegetation establishment, the flowing sand dune in most natural and artificial vegetation sites was covered with bio-crusts. The coverage degree of the crust was 50%-80%, with a thickness of 1-2 cm. In S. microstachya stand, the crust thickness, hardness, and organic matter and nutrient contents were the highest, followed by in P. sylvestris var. mongolica stand, and in A. frigida and A. frigida stands. Moss crust had higher thickness, hardness, and organic matter and nutrient contents than lichen crust. Comparing with those in flowing sand land, the physical and chemical properties of under-layer soil in test stands were improved obviously, the improvement degree being higher under moss crust than under lichen crust, and higher in S. microstachya and P. sylvestris var. mongolica stands than in A. frigida and P. simonii stands. Vegetations with moderate height and rich branches and leaves were more helpful to the development of bio-crust and the improvement of under-layer soil, because they could reduce wind velocity and accumulate more dust and litters, and the development of moss crust was more favorable than lichen crust to the improvement of its under-layer soil.