ifoam'96 Book of Abstracts 11th IFOAM Scientific Conference 11-15 August 1996, Copenhagen, Denmark

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Workshop

Biodiversity of annual legumes in the Syrian steppe.W3

1) Department of Livestock Ecology, Tropical Sciences Centre, Justus-Liebig University, D-35390 Giessen, 2) International Centre for Agricultural Research in Dry Areas (ICARDA),P.O.Box 5466, Aleppo,Syria.

Annual legumes are an important vegetation component in the Syrian steppe, which is threatened by overgrazing and by cropland encroachment. The frequency of occurrence of annual legumes as well as the environmental factors affecting the distribution of genera, species and ecotypes were studied in the semiarid and arid steppe areas in southwestern Syria.
In total, 235 ecotypes belonging to 42 species and 13 genera were identified in the steppe, and seeds were collected of all ecotypes and the soil seedbanks determined. Inspite of the marginal climatic and edaphic conditions (low precipitation, sandy and alkaline soils low in nutrient content) a considerable genetic variety was recorded.Astragalus , Trigonella , Medicago, Trifolium, and Onobrychis were the most frequently occurring genera, while others (Hippocrepis, Hymenocarpus, Melilotus, Vicia, Lotus, Lathyrus, Ononis, and Scorpiurus) were only represented by a single genus. Astragalus transjordanicus was described for the first time for the Syrian steppe. Species diversity increased with increasing precipitation from 2 species at less than 100 mm rainfall to more than 10 above 250 mm.The distribution of genotypes was affected by environmental sitecharacteristics such as rainfall, temperature, chemical and physical soilparameters, and altitude. Astragalus spp. dominated in the very arid zones,Trigonella spp. were more or less equally distributed over all rainfallzones, and the other genera showed a higher water requirement. ParticularlyTrifolium spp.were not found below 200 mm rain. Likewise, species withingenera responded variably to precipitation, temperature, to the proportionof sand or silt in the soil, and to the organic matter, phosphorus, andnitrogen content of the soil, or the soil pH. This diversity andadaptation to a wide variety of environmental conditions indicates agenetic potential for the regeneration of the Syrian steppe with annual legumes. However, in 30% of the investigated sites no seeds of annual legumes were found in the soil, possibly due to overgrazing. This my be an indicator of genetic erosion in these areas.