生物结皮影响下的土壤有机质分异特征

Influence of cryptogamic soil crusts on accumulation of soil organic matter in Gurbantunggut Desert,northern Xinjiang,China

对新疆古尔班通古特沙漠生物结皮影响下的土壤有机质分异特征进行了定量研究.结果表明,该沙漠典型沙垄不同部位具有不同的土壤有机质特征,且土壤有机质含量具有明显的分层特征.无论是结皮覆盖区还是非覆盖区,土壤有机质的积累均以表层0～5cm土层为主,由表及里呈递减趋势.这种地表有机质分布的规律在该沙漠地表普遍存在.虽然如此,生物结皮却强烈影响着地表0～5cm土层有机质的含量的积累,它的存在使得该层有机质含量极显著地高于无结皮覆盖区0～5cm土层的有机质含量(t检验,p＜0.01),表明生物结皮能显著增加地表0～5cm土层的有机质含量;而无论结皮覆盖区还是非结皮覆盖区,两者5～10cm土层之间和10～30cm土层之间的有机质含量无显著差异(t检验,p＞0.05),说明生物结皮对土壤有机质含量的影响范围仅限于表层0～5cm,对更深层次土壤的有机质含量则无显著影响.

Biological soil crust, formed by different combinations of mosses, lichens, liverworts, algae, fungi, cyanobacteria and bacteria, is a common and widespread phenomenon in desert areas all over the world thanks to its extraordinary ability to survive desiccation and extreme temperatures, high pH and salinity. Despite its unassuming appearance, biological soil crusts play a significant role in desert ecosystems, including involvement in the process of formation, stability and fertility of soil, preventing soil erosion by water or wind, increasing the possibility of vascular plant colonization, and being responsible for the stabilization of sand dunes. The present paper focuses on distribution of soil organic matter （SOM） in the Gurbantunggut desert influenced by biological soil crust. We found that the SOM content gradually decreased from inter-dunes to the top of sand dunes at each depth of soil layers in the Gurbantunggut Desert. The SOM content in inter-dune valley is higher than that on the slopes and top of sand dunes. At each location on sand dunes, the SOM was mainly distributed in the surface 0-5cm soil layer with or without crust cover. This is the general distribution pattern of SOM in this desert. However, further ANOVA analysis shows that the occurrence of biological crust in the Gurbantunggut Desert could significantly enhance the accumulation of SOM in the surface 0-5cm soil layer compared with the areas devoid of crust cover （p〈0.01）. There are no significant difference for SOM content between 5-10cm and 10-30cm soil layers （p〉0.05）. That means the biological soil crust can only influence the accumulation of SOM in the surface 0-5cm soil layer, and seldom influence the deeper soil layers. Biological soil crust can be an important source of fixed carbon in sparsely vegetated areas common throughout arid lands. Although the influence of biological crust on SOM content was only displayed in the surface 0- 5cm soil layer, the crust is likely to positively serve as an important nutrient input to the whole desert ecosystem due to its large coverage in the Gurbantunggut Desert. Particularly, the intensive accumulation of SOM in the surface 0- 5cm layer would be beneficial to growth of ephemerals and ephemeroids, which were well-developed in the Gurbantunggut Desert, thriving from early April to September. While vascular plants contribute organic matter to soils directly beneath them, large interspaces between plants receive little plant material input. Where biological soil crusts are present, carbon and nitrogen contributed by these organisms help keep plant interspaces fertile, providing energy sources from soil microbial populations. The surface intensive accumulation of SOM also enhance seed germination and seedling establishment.