Effect of Populus caspica, Alnus glutinosa and Taxodium distichum on Some Soil Chemical Properties in Forestlands of Astaneh Ashrafieh

This study compared the effects of exotic species، Taxodium distichum، with two native species، Populus caspica and Alnus glutinosa، on soil chemical properties in the Safrabasteh forestlands of Astaneh Ashrafieh region. A factorial experiment was conducted in the framework of completely randomized block design with two factors: (1) three types of tree cover and (2) two levels of sampling depth، with three replications. For each replicate، plots of 100 m2 were chosen and soil samples were taken at the center and every four corner of the plots in each depth. Then، samples of each depth were mixed and one combined sample was used for chemical analysis. Some soil properties such as pH، electrical conductivity، organic carbon، total nitrogen، humic and fulvic acid، equivalent calcium carbonate and C/N ratio were determined. The results revealed no significant difference in pH of soils under three forest cover، however، there were significant differences in the other parameters. Decrease in soil electrical conductivity was due to alluvial parent material، high rainfall in this region، and proximity to the Sefidrood River، which caused more leaching in the soil. Taxodium distichum led to increase organic carbon، nitrogen، humic and fulvic acid in soil in comparison with the two native forest covers، Alnus and populous. However، differences among interaction of forest species with soil properties observed in both depths could be due to the different qualities and quantity of litter، bush and proceses that occur in the forest floor. It also depends on root function and elemental recycling. Furthermore، C/N ratio was the lowest in soil under Alnus glutinosa cover، which is probably related to higher biological activity and nitrogen fixation. It can be concluded that Taxodium distichum has had secondary effects on the soil during the last three decades. Thus، further and more detailed studies are necessary in the future; or by using biological and biochemical indexes that give faster response to the environmental changes، the effect of various species on soil quality could be studied.