Effect of environmental factors on weed species distribution

In order to survey the effects of environmental factors on weed flora distribution, an experiment was done in Shabestar county (northwest of Iran) alfalfa fields during 2010-2011. A total of 130 weed species from 28 families were observed within these fields. Twenty six weed species as dominant species were observed in more than 36% of this county alfalfa fields. These weeds were adapted to climate and soil conditions of Shbestar different districts. Multivariate analyses with canonical correspondence analysis (CCA) showed that changes in the weed community composition were due to environmental conditions. So that, the first two CCA axes explained 50.3% of the variation in weed species distribution. The first axis represents a gradient of soil’s Zn, Daily raining, Temperature, Mn, salinity, minimum humidity, soil’s K, soil’s Fe, and daily maximum temperature and the second axis represents a gradient of salinity, elevation, soil’s Zn, K, P, and Cu. Achillea wilhelmsii C. Koch, Carthamus oxyacantha M. B., and Hordeum glaucum Steud. were tolerant the soil’s salinity, because these weeds markedly positive relationship with salinity. Cardaria Draba (L.) Desv., Plantago lanceolata L., Aegilops cylindrica Host., and Tragopogon graminifolius DC.were found frequently in the high elevations.