Poster Symposium 17 Managed ecosystems
GfÖ 2006 Bremen, P17-05
The importance of cryptogamic soil crusts in desert sand dunes M. Veste
Sand dunes cover 12% of the arid regions of the world. In these regions a major problem for desertification is the high mobility of sand dunes, which threaten arable land, roads, railways and even settlements. Biological soil crusts play an important role in these ecosystems. They are covering the upper first millimeter of the topsoil and are composed of cyanobacteria, green algae, mosses, fungi as well as lichens. In the first stage after disturbance cyanobacteria and green-algae colonize the topsoil and after the surface is stabilized lichens and mosses can be found. The importance of biological soil crusts for sand stabilisation and hydrology will be shown in examples from the Negev desert (Israel) and Inner Mongolia (China). (I) Sand dunes of the Negev (Israel): The sand dunes of the northwestern Negev are the eastern extension of the northern SinaiNegev sand field. Intensive grazing and trampling by goats, sheep and camels results in a decrease of the vegetation cover on the Egyptian side, whereas on the Israeli side the vegetation remained undisturbed. Denser vegetation developed on the Negev site. (II) Inner Mongolia (China): As most parts of the northern provinces of China, the sand dunes of the Tengger desert are heavily influenced by human-made desertification processes and natural vegetation is often completely destroyed. Artificial sand dune stabilization measures were successful [1]. The establishment of functioning crusts is important for a natural rehabilitation of degraded lands [2]. Depending from the (micro) climatic boundary condition the crusts can re-establish themselves after an initial surface stabilization. Cyanobacteria excrete exopolysaccharids which the soil particles stick together. Soil lichens develop morphological structures, which penetrate into the soil surface and enhance together with the fungal hyphae the surface stability and thus prevent wind erosion. Changes in the surface properties influence the hydrology and water re-distribution. Biological nitrogen fixation by free-living and symbiontic cyanobacteria is an important nitrogen source. Depending on the sampling location and year, the relative biological fixation of atmospheric nitrogen in the north-western Negev was estimated at 84%-91% for the biological soil crust [3]. The estimated N fixation by cyanobacterial crusts is approx. 9-12 kg ha-1a-1, whereas the annual N deposition by dust varies between 2-4 kg ha-1a-1. References [1] Veste, M, Gao, J, Sun, B, Breckle, S-W (2006) The Green Great Wall - Combating Desertification in China. Geographische Rundschau Internationale Edition 2 (3): 14-20 [2] Veste, M (2005) The importance of biological soil crusts for rehabilitation of degraded arid and semiarid ecosystems. Science of Soil and Water Conservation 3 (4): 42-47 [3] Russow, R, Veste, M, Böhme, F (2005) A natural 15N approach to determine the biological fixation of atmospheric nitrogen by biological soil crusts of the Negev desert. Rapid Communication in Mass ____________________________________________ Maik Veste, University of Hohenheim, Institute of Botany – Experimental Botany, 70599 Stuttgart, Germany,
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