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Genetic variability and differentiation of six populations of Tilia rubra from Hyrcanian forests of the north of Iran were analyzed using random amplified polymorphic DNA (RAPD) markers. Seven primers pairs used to study six populations, in six localities located in at different altitude (250–2500 m a.s.l) but within the distance 50 km, provided 70 reliable bands, of which 29 (41.4%) were polymorphic. The average population diversity using the Shannon’s index (I) was 0.22 and ranged from 0.22 for Bandbon population to 0.08 for the Salahedinkola population. The mean heterozygosity varied from 0.013 to 0.06 within the populations of T. rubra. The AMOVA analysis showed a significant genetic differentiation within populations and 97% of the total variation occurred within populations and only 3% occurred among populations. Cluster analysis using the UPGMA method grouped all individuals into four clusters. The results did not correspond with the populations origin. The low inter-population differentiation and the lack of significant correlation between geographic and genetic distances suggest intensive gene flow among populations of Tilia rubra.
We compared soil properties beneath naturally-occurring patches of Lycium ruthenicum Murray (fam. Solanaceae) to evaluate the shrub’s potential to improve the fertility of saline soils. Soil pH, total nitrogen and carbon and extractable potassium, magnesium and phosphorus were respectively significantly higher in the A and B horizons of Lycium shrub patches compared to adjacent unvegetated soils. The influence of Lycium on these soil properties increased with shrub density. Total soil N and extractable Mg and K concentrations were 1.8, 2.6- and 6.6-fold higher under dense Lycium shrub patches compared to unvegetated, bare areas and soil pH was 0.5 units higher. In contrast, the presence of shrubs and shrub density had no clear affect on the EC, Na or CEC of the A horizon soils. The shrub effect extended to the gypsum-rich By horizon (20–50 cm depth) and underlying B horizon (30–80 cm depth) for several soil properties. Total soil C and N were 1.8- and 1.6-fold higher beneath dense Lycium patches than bare soil areas. Soil pH remained 0.4 units higher under dense Lycium than bare soil patches. In the B horizon total soil C was twice as high beneath dense Lycium patches compared to the other patch types. Lycium ruthenicum not only tolerates the saline and drought conditions, it also produces sufficient biomass to increase the nutrient and organic matter content of surface mineral soils in this arid ecosystem and may have potential to improve soil conditions, facilitate ecosystem development and slow desertification.
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